161398 i _-------^ ,i#ll I !'»■ ■—^a Surgeon Ganeral's Office cftc/i'on,---- w/-.o.a:u<(H. [^^gGgQ CXIu i^J Cmj CDOCOO C ■ fo?Oue^ 4 r». *5 .* '* #> 1 5E« '-i -Jr?i te DUE TWOWEEKS FROM LAST DATE MAR 5 1958 MAR 9 1961 ■"<*, >.'$! 1 / - *^§5i£2s\ o fr* igKAfC^ .?. rn; it-MT jit ni «"J5^^ Drai;-n arid £fny/a- ty. ^"..9. <_• ''' HARPLk f- hF;'.". r':7/ . .« OF MAN" L. d a AN ELEMENTARY TREATISE ON HUMAN PHYSIOLOGY, ON THE BASIS OF THE PRECIS EliMENTAIRE DE PHYSIOLOGIE. PAR F. MAGENDIE, MEMBRE DE L'lNSTITOTE DE FRANCE, &C, &C, &C. FIFTH EDITION. 1838. TRANSLATED, ENLARGED, AND ILLUSTRATED WITH DIAGRAMS AND CUTS. ESPE- CIALLY DESIGNED FOR THE USE OF STUDENTS Ot MEDICINE. BY JOHN REVERE, M.D., PROFE8SOR OF THE THEORY AND PRACTICE OF MEDICH^ IN THE .UNIVERSITY OF THE CITY OF NEW-YORK. ^ZifM GEICL^ V NEW-YORK: IIARPER Use nnknown. Ear J o*v rm. x? * i Surrounds the organs, and protects them by 8th. The b at .... J their physical properties. 9th. The Marrow . . . Fills the cavities of the bones. i/ui. r™. a • I Favours motion by diminishing the friction of 10th. The Synovia . . . } the movable surfaces in contact. 11th. Serosity of the Cellular Tissue Use analogous to that of the synovia. 12th. Seronty of the Serous Mem- J Lnbricates the surface of these membranes. the Sweat .... £ of the body. 14th- Tsek£nctutms Humour of the \ Favours its contact with forei^ bodies- ,-»!, M___„ \ Covers the mucous membranes, and protects 15th. Mucus . . . . \ from injurious contact 16th. The Gastric Juice . . Dissolves the aliments in the stomach. J7th. The Pulmonary Transpiration Concurs in respiration. 18th. The Liquid that fills the cells ^ of the Thymus 19th. The Liquid of the Thyroid Body .... 20th. The Liquid that fills the Cap- sula Renales , 21st. Chassie .... Facilitates the motions of the eyelids and eyes. 22d. The Cerumen . . . Protects the auditory passage. 23d. TheHumourattheRootsof the J Fieser/ea thdr flexibility. 24th. The Sebaceous Humour on the ) r ., ,. . . externalsurfaceoftheOrganst £"™» the friction, and opposes the pressure of Generation . . ^ which the genital organs undergo. 25th. The Tears j Protect the eye, and are means of expression. 26th. The Bile .... ) ,, , .. 27th. The Pancreatic Juice , J Concur in digestion. 28th The Urine i . T^e Tes^ue °f tne chemical operations of the (body. 29th. The Chyle . . . Fluid nutritive extract of the aliments. ' All these liquids, and some others not mentioned, are common to both sexes. Uses unknown. PRELIMINARY OBSERVATIONS. 21 Useful in generation. The fluids peculiar to man are, 1st The Prostatic Humour . Contributes to fecundation. 2d.' The Fluids of the Sub-Prostate ) Uses unknown< Glands J 3d. The Semen .... Fecundating fluid. The fluids peculiar to women are, 1st. The Milk .... To nourish the infant. 2d. The Fluid of the Vesicles of the Ova-' ria .... 3d. The Liquid of the Corpora Lutea 4th. " " Chorion . 5th. " " Amnion . 6th. " " Umbilical Vesicle The physical and chemical properties of the fluids are very va- rious. Many resemble each other, but no two are precisely alike. At all times, great importance has been attached to a methodical arrangement of them, and we find that different classifications have been adopted, according to the prevailing doctrines of the schools at different periods. Thus, the ancients, who laid great emphasis on the influence of the four elements in the operations of Nature, asserted that there were four principal humours in the body, viz., the blood, the lymph, the yellow, and the black bile; and that these four humours corresponded to the four elements, the four seasons of the year, the four parts of the day, and the four temperaments. In more modern times, other divisions have been substituted for this classification of the ancients. Thus, they were at one time divided into three classes, viz., 1st, the chyme and chyle; 2d,the blood; 3d, the humours secreted from the blood. Some authors have thought it sufficient to arrange them into two classes: 1st, fluids which are useful as aliments; 2d, those which are useless in this respect. The first are called recrementitial, that is, hu- mours which, after their formation, are destined to nourish the body ; the second, excrementitial, or those which are thrown out of the economy; those humours which participate in these two characters have, for this reason, received the appellation of excre- mento-recrementitial. Chemists have lately endeavoured to clas- sify the humours according to their peculiar nature; as the albu- minous, fibrous, and aqueous humours, &c. But the classifica- tion of Professor Chaussier will be found to be the best. This has no regard to the nature of the fluids, or the uses to which they are destined, but is founded on the mode of their formation, the only character which remains always the same. The following is his classification: 1st. The Blood. 2d. The Lymph. 3d. Perspiratory fluids, which comprehend the cutaneous trans- piration ; the transpiration of the mucous, serous, synovial, cellu- lar, adipose, and medullary membranes, the interior of the thyroid thymus, the eye and ear. 4th. The follicular fluids; the fatty humour of the skin, the se- baceous humour of the eyelids, the mucus of the glands and fol- 22 PRELIMINARY OBSERVATIONS. licles of the tonsils, the cordia and parts about the arms and pros- tate, &c. 5th. The tears, saliva, pancreatic juice, bile, urine, the fluid of the glands of Cowper, semen, milk, of the capsulae renales, the mammae, and the testicles in new-born children. 6th. The chyme and chyle. But the number of the humours is not so great that it is neces- sary to classify them. There is no difficulty in studying '.hem separately. When once known individually, all classification be- comes superfluous. Physical Properties of the Fluids. These are of considerable importance: those to which we have already referred are viscidity, transparency, colour, odour, &c. The viscid fluids are found wherever there are membranes to be preserved, friction to be diminished, and polished surfaces to be lubricated. Transparency is especially found in the fluids of the organ des- tined to act on light. Many other fluids present this character to a greater or less degree. The colours of the fluids vary but little; many of them are col- ourless. Red of different tints, yellow, and black are the chief colours; even these result from two colouring matters, which, by their dif- ferent modifications, produce all the other shades. The odours of the fluids are very various. Certain fluids present to the microscope a remarkable appear- ance ; there are myriads of globules of a regular form and con- stant size. These globules are particularly met in the blood, lymph, chyle, and milk. The semen, when examined by the mi- croscope, often exhibits a great number of minute animals, which move with great agility. But the presence of these singular be- ings is far from being as uniform as the globules of which we have spoken. They are only observed during certain periods of life and in health. Chemical Properties of the Fluids. The chemical qualities of the fluids are interesting to the phys- iologist. Many of the important vital actions depend immedi- ately on these properties. Unfortunately, this part of the science is at present but little advanced; nevertheless, chemistry has furnished some useful information on this subject. We know that the composition of the fluids does not differ essentially from the solids. There are the same immediate principles and the same el- ements. If we drive off by evaporation a part of the water which many of the fluids contain, we obtain a semi-solidified mass, which has a great analogy in its composition with the true solids. This is not surprising, as in the living body the fluids are continually transformed into solids, and the solids into fluids. Most of the fluids exhale carbonic acid, and absorb oxygen from the air. Gen- PRELIMINARY OBSERVATIONS. 23 erally speaking, the fluids have a stronger tendency to decomposi- tion than the solids. The immediate principles of the fluids also contain more azote, or caseum and urea, which are most rapidly decomposed. Vital Properties. Besides the chemical and physical properties of the solids and fluids, we also witness many phenomena not observed in inorgan- ic matter, which constitute the essential characters of life. It would have been wise to have studied each of these phenomena separately, and to have thus acquired a precise notion of the spe- cial attributes of living organized bodies. But to obtain such a result, which would be capable of so many useful applications, it would be necessary to separate carefully in the living being that which is chemical or physical from that which is purely vital. Now this distinction has always been found impracticable, from the imperfection of our means of physical analysis. Even at the present time, when these means have acquired a greater degree of certainty and precision than at any former period, this distinc- tion would be found extremely difficult, and would require for its execution a mind of a peculiar cast. But this course has not been adopted. There have been established, or, rather, imagined, cer- tain vital properties, and it has been consequently affirmed that living bodies are in a perpetual struggle with the general laws of Nature ; an idea inexpressibly absurd. That the ancients should have believed that such a struggle existed between the laws which govern the microcosm or little world, and the macrocosm or uni- verse, is not surprising, when we recollect their ignorance of both organic and inorganic bodies. But now that the physical sciences have become so much improved, and made us acquainted with many very important laws of Nature, we perceive that these laws exert an evident influence upon animals. It is true that the living organs present phenomena which cannot be explained by mere physical laws, but it does not follow that they are opposed to each other; that there should be, for example, any opposition between sensibility and gravity, or between contractility and chemical af- finity. These things are only different, not contrary to each other. . The vital properties, as generally admitted, have received dif- ferent names. 1st. Organic Sensibility, nutritive, vegetative, and molecular. 2d. Organic Contractility, insensible, nutritive, and fibrillous, tone, tonicity. 3d. Cerebral Sensibility, animal, perceptive, &c. 4th. Sensible organic Contractility, irritability, vermicular mo- tion, utr .,!•,.• 5th. Voluntary Contractility, animal, of relation, &c. Of these properties, some are considered common to all living bodies, others peculiar to certain parts of animals. If they existed, the first only would deserve the name of vital 24 PRELIMINARY OBSERVATIONS. properties, inasmuch as they are characteristic of life wherever it is found. But many of these properties have no real existence; they have been imagined by physiologists, to enable them to ex- plain phenomena beyond the reach of our senses, and, consequent- ly, unknown. Our organs nourish themselves, but we are igno- rant of the mode by which this vital act is accomplished. To be- come acquainted with it, it would be necessary to make many experiments, and to invent instruments which would subject to our examination things that are beyond the cognizance of our senses. The substitution of a fiction has been found more sim- ple and easy. " Thus it is said the organs are composed of mole- cules, which are sensible (a mere gratuitous supposition); they distinguish, in the nutritious fluids which are presented to them, the elements which are fitted to repair their waste." Thus it ap- pears that these molecules are endued, not only with sensibility, but discernment. But, in supposing that the molecules are capa- ble of discerning the materials suitable to repair their waste, but half the phenomena is explained; it is also necessary that they should appropriate these materials. It has been attempted to re- move this difficulty by the supposition of insensible contractility ; but it is not easy to imagine by what sort of motion a molecule can seize upon the nutritive materials. Who does not see, in this little history, a mere metaphor of the history of an animal or of man ? It is the anthropomorphism of the philosophers applied to molecules. The most curious part of it is, that the mind can rest satisfied with such mystification. This is not all, the romance is pushed still farther: it is neces- sary to explain diseases which are an exaltation, or weakening or perturbation of the vital properties ; hence therapeutics, the object of which is to restore the vital properties to their normal type. This is the foundation of systematic medicine. The student of medicine knows no way of avoiding this: the only way to do so is to learn early to say to himself, / do not know; this is the first step towards discovering the truth. The other vital properties are peculiar to certain animals, or, perhaps, to some part of them; such is sensible organic contrac- tility, as seen in the heart, alimentary canal, bladder, &c, but which is not observed in other parts of the economy. Cerebral or animal sensibility, according to Bichat, as well as voluntary contractility, can only be accounted among the number of vital properties by an abuse of terms. It is evident that these are the functions or the results of the actions of several oro-ans, which have one common end. We shall say nothing of the force of vital resistance, vital affinity, caloricity, &c, because these pre- tended properties, though proposed by men of ability, have not excited much attention among physiologists,,and, besides, have not more reality than most of those of which we have spoken. The doctrine of the vital properties have not, fortunately, been applied to the fluids, though they are admitted to possess life. A much more philosophical method has been pursued with respect PRELIMINARY OBSERVATIONS. 25 to them; for it was not admitted that they were endowed with life until this was proved. Thus their vitality has been inferred from their preserving their fluidity while they remain in certain parts of the living body; the plastic powers of some, and their capacity to evolve caloric. These are the principal phenomena which, ac- cording to some modern physiologists, indicate the life of the fluids. But only the blood, lymph, chyle, and a few others of the fluids destined to nutrition, present these characters. The excrementi- tial fluids, as the bile, urine, cutaneous transpiration, &c, do not possess these qualities ; hence, what is called the vitality of the fluids does not exist in the latter. Causes of the Phenomena peculiar to Living Bodies. From the earliest antiquity, it has been observed that the great- er number of phenomena which take place in living bodies are essentially different from those that occur in dead, inorganic mat- ter. One particular cause has been assigned to explain the phe- nomena observed in living bodies. This cause has received dif- ferent names. It was denominated by Hippocrates, fyvoie (Na- ture) ; by Aristotle, moving and generative principle; by Boer- haave, impetum faciens; by Van Helmont, archea; by Staal, soul; others, again, have called it vis insita, vis vitce, &c. M. Chaus- sier, in his learned lectures, and in his synopsis of the characters of vital power, has adopted the name "force vitale."* It is not worth while to endeavour to deceive ourselves by this expression, "force vitale" or vital power. It does not and cannot mean anything else than the unknown cause of vital phenomena. But what signifies all these expressions ? They must have one of two meanings: either that of entities, to which belong the pow- er of producing vital phenomena; but, in supposing this, do we not resemble savages, who, after having rudely sculptured a stone, call it a God ? Or we assert that these words, force vitale, desig- nate the unknown, and, perhaps, incomprehensible cause or causes of vital phenomena. If the latter, it must be confessed that science has gained nothing by these inventions. In the same manner, say these physiologists, as attraction pre- sides over the changes of state in dead matter, does the vital pow- er control the modifications of organized bodies. But they fall into an error, for vital power and attraction cannot well be com- pared to each other; the laws of this last are perfectly known; those of vital power entirely unknown. Physiology is, at this time, precisely in the state in which the physical sciences existed before the discoveries of Newton, and it requires a genius of the highest order to discover the laws of vital power, in the same manner as Newton made known those of attraction. The glory of this great man does not consist in having discovered attrac- tion, as some believe, for before his time this cause was known, but in having shown that this power " acts directly in proportion to the mass, and inversely as the squares of the distances." * See the Synoptic Table of the Fluids. D 26 PRELIMINARY OBSERVATIONS. v But it is not by speculations in the closet that this point can be attained. An exact knowledge of the physical sciences, numer- ous experiments upon living animals, both in health and disease, together with the most severe and rigorous modes of reasoning, can alone lead to this. Before beginning the examination of the phenomena of life in man, the principal object of this work, we will make one general remark. Whatever may be the number and diversity of phenom- ena presented by man during life, they may be reduced at last to these two principal ones, viz., nutrition and vital action. A few words respecting each of these phenomena are indispensable to the proper understanding of those subjects which will hereafter fall under our consideration. The life of man, and that of other organized bodies, is preserv- ed by the habitual assimilation of a certain quantity of matter, called aliment. If they are deprived of this for a given period, it will be necessarily followed by a cessation of life. On the other hand, daily observation shows that the organs of man, and other living beings, are constantly losing a certain portion of the matter of which they are composed. A necessity, therefore, for repair- ing the loss which is thus constantly sustained, is the reason why the habitual use of aliments is required. From these data, and from some other circumstances which we shall mention by-and- by, it has been justly concluded that living bodies are not compo- sed, identically, of the same matter at every period of their exist- ence, but that they undergo a total renovation. The ancients imagined that this was accomplished in the space of seven years. But, without admitting this conjecture to its full extent, it is ex- tremely probable that all parts of the body, during life, are under- going a change, which has the double effect of expelling those molecules which have served their appointed time in the compo- sition of the organs, and of replacing them by new molecules. It is this which constitutes nutrition. This process does not fall, in- deed, under the cognizance of our senses; but the effects are so palpable, that it would be the height of skepticism to doubt it. In the present state of physiology, this operation cannot be attribu- ted to chemical affinity, that power which controls the action of minute particles of matter upon each other in dead bodies, nor, in- deed, do we know of any satisfactory explanation of it. To say that it depends on organic sensibility, or organic insensible con- tractility, or simply on vital power, is only to express the fact in different terms, without giving any explanation of it. But how- ever this may be, we can only attribute to this process of nutrition the power of living bodies to preserve or change the physical properties of their organs. Our different organs being found to present different physical properties, the process of nutrition must no doubt vary in each. Independently of the physical properties which all parts of the body present, there are a considerable number which exhibit, either continually or periodically, a phenomenon which has been PRELIMINARY OBSERVATIONS. 27 called vital action. The liver, for example, is endued with a pe- culiar power, by which it is enabled constantly to form a fluid called bile; the same remark may be applied to the kidneys in the formation of urine. The voluntary muscles, under certain circum- stances, grow hard, change their form, and contract; this is an- other example of vital action. These vital actions are of great importance in the life of man and other animals, and particularly demand, therefore, the attention of the physiologist. Vital action evidently depends on nutrition, and nutrition is re- ciprocally influenced by vital action. Thus an organ which ceases to receive nutrition soon loses its power of vital action; and organs, the action of which is frequently repeated, possess more active powers of nutrition, while in those, on the other hand, which act but little, the process of nutrition is evidently slow. The precise mode in which vital action is performed is un- known. There takes place in the organs some insensible move- ment of its molecules, which can no more be explained than the process of nutrition. No vital action, however simple it may ap- pear to be, can be considered an exception to this rule. All the phenomena of life, therefore, may be included under these two heads, viz., nutrition and vital action; but, as the pe- culiar action of the particles which constitute these two phenom- ena cannot be perceived by our senses, this is not a point upon which we can profitably bestow much attention. We must con- tent ourselves with investigating their results ; that is, the physi- cal properties of the organs, the sensible effects of the vital ac- tions, and the manner in which these concur in the general pro- cesses of the living body. This is, in fact, the end of physiology, and, to attain this end, the phenomena of life have been divided into different classes, or functions. CHAPTER II. CHARACTERISTICS OF MAN. [In the conformation of man there are certain peculiarities which are worthy of attention. One of the first of these circumstances is his erect attitude and commanding presence. In these respects he strikingly differs from and surpasses all other animals. This attitude not only imparts dignity to his appearance, but gives him great advantages in many of the conditions in which the high career to which he is destined necessarily places him. When we examine his organization, and compare it with that of the other mammalia, we perceive that in him all the details are adapted to an habitual erect posture and progression, while their conformation is such, that though some of them can assume this 28 CHARACTERISTICS OF MAN. position, and preserve it for a time, yet that its continuance is in- convenient and unnatural. Man is Bimanous and Biped. The animals which approach nearest to the human subject are monkeys, which are hence called anthropomorphous. But even the most perfect of them differs from him, in many important par- ticulars. In man the superior and inferior, or pectoral and ab- dominal, members differ essentially. The great muscular strength of his lower extremities, their expanded, wide-bearing joints, their firm attachment to the trunk, their comparatively limited motion, and greater length, compared with the superior members, all indi- cate that they are designed for locomotion and supporting the weight of the body, thus leaving to the upper extremities the most perfect freedom of action. On the contrary, the small size of his arms, their great extent of motion, comparatively loose articulation with the trunk, and especially the admirable conformation of the hand, with its long, delicate fingers, flexible joints, and highly-de- veloped antagonistic thumb, indicate its entire unsuitableness to these purposes, and show that the offices to which they are destined are widely different. When we contemplate the exquisite mech- anism of the human hand, and the many brilliant triumphs of art executed by this wonderful member, we are not astonished at the enthusiasm of the ancidnt philosophers, who attributed the great superiority of man to other animals chiefly to the possession of this surprising instrument. Thus, man possesses two hands and two feet, the offices of which are essentially different; a conformation which does not exist in other mammalia, which have either four feet or four hands. The simiae have four hands, the abdominal extremities being furnished with an imperfect antagonistic thumb, and capable of grasping objects precisely like the pectoral members; while the latter, as well as the former, are obviously designed for support and progression. Among the peculiarities in the structure of the lower extremities in man which impart to him the power of erect posture and progression, are his large astragalus and the great mass of muscles attached by their tendons to its posterior project- ing process, constituting the calves of the legs. Other animals are destitute of these arrangements. In none of the anthropo- morphous animals are these parts developed; hence, when in an erect posture, they stand on the sides of the feet, and their gait is necessarily constrained, tottering, and unsure. The inferior extremities in man are also remarkable for their length as well as great muscular power. They are as long as the head and trunk united, which does not occur in any of the monkey tribe. This facilitates his erect attitude and locomotion, while it renders progression in a horizontal posture difficult and laborious. On the contrary, in the apes, the pectoral are gener* ally longer than the abdominal members; in the orang-outan the hands reach to the ankles. CHARACTERISTICS OF MAN. 29 Vertebral Column. The Spinal Column in the human subject presents also some peculiarities that deserve attention. Its outline is that of a trun- cated pyramid, the lumbar portion being much the largest. It is not straight, but waving in the antero-posterior direction, in which it differs from that of other animals. The manifest object of these curves is to assist in an equal distribution of the weight of the trunk, and are such that a vertical line drawn from its summit would fall in the centre of its base. The spinous processes of the lumbar vertebrae are proportionally more prominent and stronger than in other animals. This is evidently designed to favour the attachment and action of those muscles which counteract the tendency of the body forward, arising from the weight of the abdominal and thoracic organs. On the other hand, the spinous processes of the dorsal and cervical vertebrae are much smaller than in those animals whose position is naturally horizontal, as they require in the latter great prominence and strength for the attachment of the powerful tendons and muscles which support and move the head and neck. Pelvis. The form of the Human Pelvis is also highly characteristic. Its expanded ilia, shallow symphisis pubis, and incurvated sacrum terminating in the coccyx, form a shallow, basin-like cavity wide- ly different from the elongated ilia and straight sacrurn of the simiae and other mammalia. The sacrum, which greatly exceeds in size that of other animals, presents at its upper part a firm basis for the support of the vertebral column, while its lower part, terminating in the os coccygis, projects forward so as to form a strong bony resistance at the inferior opening of the pelvis. The strong, expanded bones of the pelvis form suitable points for the attachment of the large muscular masses required to support the trunk upon the inferior extremities. To its posterior surface are attached the powerful glutaei, the largest muscles of the body. This part is rendered more prominent by large adipose deposites, which, together, form the nates. The buttocks, like the calves of the legs, have been considered by both ancient and modern physiologists among the most striking characteristics by which man is distinguished from other animals. Thorax. The form of the Thorax is likewise evidently modified by the erect posture to which man is destined. It is flattened at its an- terior part, but expands laterally, and is very capacious. This arrangement spreads apart the shoulders, and is favourable to the free motion of the arms, while it diminishes the weight of the body anteriorly. It is alleged that in no other animal is the an- tero-posterior less than the lateral diameter of the chest. It dif- 30 CHARACTERISTICS OF MAN. fers widely in this respect from the narrow, keel-shaped thorax of quadrupeds. Head. In tlie Head are lodged numerous important organs, developed in various degrees in different animals, which necessarily leads to great variety in the form of this part. It is the seat of the en- cephalon, the great controlling power of the body; of the organs of the senses, and is intimately connected with deglutition and respiration, the chief organs by which animals are related to ex- ternal objects. From the nature of these organs, it is obvious that they must be variously developed, and that their dimensions, form, weight, and arrangement must necessarily vary in differ- ent animals, according to their destined attitude and habits. The predominant character of man is intellectuality, while his senses are subordinate to this function more than other animals. The encephalon or cranial portion of the head is therefore devel- oped in him in a corresponding degree. The prominent charac- teristics of other animals, on the other hand, are much more inti- mately connected with one or more of the other organs, the intel- lectual functions being altogether subordinate. These circum- stances, with their natural attitudes, thus furnish a key to the pe- culiarities observed in the head of man when compared with other animals. The head is obviously divisible into those parts occupied by the organs of the senses, or the face, and the enceph- alon. One of the most remarkable circumstances observed in contrasting the head of man with other animals is his large cra- nium and small face. It will be found generally true in all an- imals, in the outline presented by a vertical section of the head in the antero-posterior direction, that, as the proportion of the cranium exceeds that of the face, the intelligence increases, and vice versa. This rule holds generally good, not only as regards different animals, but the various tribes of men. Camper pro- posed what he called the facial angle as a simple, and, generally, accurate method of expressing these proportions. Supposing the skull to be viewed in profile, and a line drawn from the greatest projection of the forehead to that of the upper maxillary bone, this may be called the facial line. If a second line be drawn from the meatus auditorius externus along the floor of the nasal fossa?, so as to follow the direction of the base of the cranium until it touches the first line, the angle thus formed will be the facial angle of Cam- per. It is evident that this angle will increase as the anterior portion of the cranium becomes developed and the face smaller, and the reverse as the face is more prominent and the forehead retreating. This angle is about 80° in the Caucasian race ; about 70° in the negro; while in the different varieties of monkevs it varies from 60° to 30°. y The following figure represents an outline of the skull of the negro, with the lines which form the facial angle of Camper. CHARACTERISTICS OF MAN. 31 A B is the facial line ; C D the second line passing through the auditory passage. As we descend in the scale of animals the facial angle becomes very acute. Thus in the horse, as will be seen in the following figure, the forehead is very retreating and the angle very acute. In some of the birds and reptiles it cannot be measured. The ancient Greek artists appear to have been aware of the majesty imparted to the human countenance by a large facial angle. Thus, to give effect to their representations of the gods and distin- guished men, they exaggerated this angle much beyond what oc- curs in nature, carrying it to 90°, and even farther. But in their finest statues it does not exceed this. When pushed beyond this point it causes obvious deformity. (Fig. 2.) On examining the base of the cranium, we find indications sim- ilar to those above described. In man, the foramen magnum, through wThich the medulla spinalis passes to the spine, is placed nearly in the centre, but a little posteriorly, so as to counteract the greater weight of the posterior portion of the head. Still the head is not exactly balanced when the person is erect and all the muscles relaxed, but inclines anteriorly. But this is prevented generally by the action of the muscles attached to the occiput, by which the head is kept erect without a consciousness of effort. In quadrupeds, the natural posture being horizontal, the foramen magnum is placed near the posterior part, instead of the centre of the base of the cranium. This is strikingly shown in the fol- lowing delineation of the base of the cranium in man and the orang-outan, after Mr. Owen. In other mammalia, e. g., the horse, as shown figure 2, this pe- culiarity is still more remarkable ; the foramen magnum is placed at the back of the skull. In this class of animals the head is attached to the spine, and kept in place by a strong ligament, the ligamentum nuchae, which extends from it to the spinous 32 CHARACTERISTICS OF MAN. (Fijr. 3.) processes of the cervical and dorsal vertebrae. But, as there is scarcely a vestige of this ligament in the human subject, and from the great weight of his head, standing in a horizontal posture is necessarily unnatural and painful to him. In man, as we have seen, especially in the Caucasian race, in which the facial angle is large, the forehead is nearly on a line with the face. But this arrangement does not exist even in the most anthropomorphous animals; on the contrary, the face pro- jects far beyond the forehead, so that in them the anterior lobes of the brain are not placed over it, as in the human subject. This prominence of the face, or, as it is more commonly called in the in- ferior animals, the muzzle, is adapted to the horizontal posture, and is favourable to the development and action of the organs placed in this part. The nose or snout in many of the quadrupeds is a highly-developed organ, and occupies a considerable portion of the face; while in most animals the mouth is not merely destined to mastication, but is the chief organ of prehension and weapon of offence and defence. Hence the size and form of the nose and mouth in man differ essentially from them. The mouth in man is chiefly destined to mastication, taste, and speech; it does not, therefore, present the strong and widely-expanding jaws, power- ful muscles, and formidable fangs so characteristic of many an- imals. Even the mouth of the orang-outan, with its elongated jaws, its short, strong incisors, and formidable cuspidati teeth, is very different from the small, arched mouth of man. It is also quite evident that this development of the muzzle in quadrupeds is in keeping with their horizontal posture. Finally, when we compare the outline presented by man with that of the orang-outan, the most manlike of the simige, we are particularly struck with the length and power of his lower extrem- ities, the breadth and solidity of the feet, with the strong project- ing os calcis, and the vast muscular masses by which they are moved, especially the powerful glutaei and gastrocnemii muscles CHARACTERISTICS OF MAN. 33 These, together with the short arms, broad pelvis and chest, the graceful position of the head upon the vertebral column, the small face, the noble, expanded forehead and capacious cranium, impart an imposing majesty to his appearance, which forms a remarkable contrast to the most perfect of those animals which most nearly resemble him.* Intellect. But though man surpasses other animals in the grace and dig- nity of his person, yet uvmany respects he is inferior to them in his physical constitution. In muscular strength, offensive and de- fensive weapons, the certainty of his instincts, the acuteness of his senses, in provisions against the inclemency of the weather, and the protracted helplessness of his childhood, his inferiority is ob- vious. How, then, has he acquired those great advantages which place him, out of all comparison, at the head of the animal king- dom ? This is chiefly attributable to a peculiarity which consti- tutes by far his highest distinction. We refer to his intellectual endowments, the mens divinior; all his other gifts are chiefly available as they are the ministers of his intellect. One of the most obvious and effectual means of acquiring his superiority over other animals is combining his efforts with others of his species. Man is naturally and necessarily social. The life of a solitary individual, notwithstanding all that fiction has ima- gined, must be unavoidably precarious and miserable. He is prompted not only by his instinctive tastes, but by a perception of his individual weakness and collective strength, to seek the so- ciety of his fellow-man. • To counteract his deficiency in mere physical strength and natural weapons, he taxes his ingenuity and industry, and procures those which are artificial, and which are in some respects superior to the natural arms of other animals, which are always few in number, incapable of improvement, and their usefulness necessa- rily limited to the individual. But man can imitate most of these contrivances and multiply them at his pleasure, and thus unite in himself all the varied endowments of other animals. They are not only available to himself individually, but may be imparted to those associated with him, and transmitted to those who come after him. An immense range of objects is thus brought under his con- trol. Every department of nature is made subservient to his pur- poses. The qualities of the fleetest and strongest animals are ap- propriated to his use, as if they were his own; the fiercest are dragged from their burning deserts as trophies of his power; the depths of the seas are made to render up their gigantic inhabitants for his convenience and luxury; while the earth, vexed by his la- bour and skill, is compelled to yield her choicest treasures, her loveliest forms, and most fragrant perfumes, for the gratification of his senses. He is thus enabled to provide not only for his first and most * See the Frontispiece, outline of Man and the Orang-outan. E 34 CHARACTERISTICS OF MAN. urgent wants, but to attend to those circumstances which improve his intellectual powers, invigorate his health, prolong his life, and embellish his existence. But though the strong distinctive character of man is his intel- lect, yet this power is by no means exclusively confined to him. Among the inferior animals we find their instinctive perceptions stronger, their affections and passions more ardent, their memory tenacious, and undoubted evidences of thought, reasoning, and imagination. The difference of intellect, then, is rather in degree than kind, though that difference is vast. But he possesses a few faculties of which other animals are destitute. One of the most striking of these, and which is inti- mately connected with his intellect, is the vast power and flexi- bility of his voice, and his capacity of inventing and uttering ar- ticulate words, by which he is enabled to communicate the slight- est differences or shades of thought. This is a most copious and unfailing source of social enjoyment and happiness, as well as of* moral and intellectual development. Another of these peculiari- ties is his capacity for improvement. Other animals rapidly at- tain their highest degree of development, and then remain station- ary. If any individual happen to possess any superiority, he is incapable of imparting it to others ; thus all successive generations remain in nearly the same .state. How different in this respect is man ! The degraded Hottentot, or native of New South Wales, scarcely equals the inferior animals in the moral dignity of their character. But how striking the contrast which civilized man presents! No one can predict the elevation to which the human character is ultimately destined. But when we look back at what has been actually accomplished, even within a short time, we are dazzled by the possibility of the future. But perhaps the most remarkable of these characteristics, and the last to which we shall allude, is his consciousness of, and sense of, accountability to an overruling and resistless power, which is neither seen, nor heard, nor appreciable by any other of his senses. Some have alleged that the existence of a God is an obvious and unavoida- ble deduction of reason; that the admirable order and adaptation of everything we see necessarily implies design, and this design a designer. But though it be admitted that the wonders of nature that everywhere surround us proclaim to the enlightened mind the present God; though reason undoubtedly comes in with its high sanctions to confirm and regulate the suggestions of this re- ligious or moral sense, yet it would seem that this is an original endowment, written in our very constitution, and to a certain ex- tent independent of, and superior to, reason. Other animals, as we have seen, possess reasoning powers, but man is the only in- habitant of this planet that gives any evidence of his conscious- ness of the existence of such a power, and of certain moral du- ties and obligations as a means of conciliating this being. It is this alone that enables him to paint the dark and mysterious fu- ture with a thousand brilliant, flattering hopes, and " to place, as SENSE OF VISION. 35 it were, a crown of glory on the cold brows of death." This fac- ulty shows itself under a great variety of forms, and is mingled in many instances with grossness and absurdity. It exists in differ- ent degrees of power in different individuals. Like the other fac- ulties, it is developed and strengthened by cultivation and exercise, and by neglect shrinks away and almost disappears, or it may be exalted to disease. But its universality, its exact adaptation to our wants and situation, its influence on our present happiness, and the exalted motives of action that it holds out, all conspire to render this the noblest attribute of our species.—Ed.] CHAPTER III. CLASSIFICATION OF THE FUNCTIONS. Authors have differed much in their division of the func- tions. Without stopping to enumerate the different classifications that have been adopted at different epochs of science, which does not comport with the nature of this work, we shall divide the func- tions, 1st, into those which connect the individual with surround- ing objects ; 2d, those of nutrition; 3d, those which have for their aim the reproduction of the species. We may call the first func- tions of relation; the second, functions of nutrition; and the third, functions of generation. The method to be pursued in the investigation of a function is by no means a matter of indifference. The following is the one which we have adopted: 1. General idea of function. 2. Circumstances which keep up the action of organs, and which we call excitants of functions. 3. Concise anatomical description of the organs concurring in any function, and which may be called its apparatus. 4. The action of each organ in particular. 5. A summary showing the utility of the function. 6. The relation of the function to the parts before examined. 7. The modifications which the function exhibits, according to age, sex, temperament, climate, season, and habit. THE FUNCTIONS OF RELATION. VISION. The functions of relation include Sensation, Intelligence, Voice, and Motion. Sensations are those functions which are destined to receive impressions from external objects, and to convey them to the sen- sorium. These functions are five in number, viz., Seeing, Hearing, Smelling, Tasting, and Feeling. 36 FUNCTIONS OF RELATION. Vision is the function by which we become acquainted with the size, figure, colour, and" distance of bodies, &c. The organs which compose the apparatus of vision act under the influence of a particular excitant, called light. We perceive bodies, and become acquainted with many of their qualities, although they may be at a considerable distance from us; there must, therefore, be some intermediate agent between these objects and our eyes; this agent is light. Light is supposed to be an exceedingly sub- tile fluid, which emanates from a class of bodies called luminous; as, for example, the sun, fixed stars, ignited substances, and those that are called phosphorescent, and is composed of particles which move with a prodigious velocity. [But we know nothing of the intrinsic nature of light; we can only conceive of it and study its properties. This would be the logical course, but we are not satisfied with this; we require a supposition upon which the mind can repose itself, and, as it were, go to sleep. It was supposed by Newton that light emanates, in the form of molecules, from luminous bodies. Des Cartes proposed another hypothesis. He supposed that space was filled with a very subtle fluid, the ether, and that luminous bodies caused vibra- tions or undulations in this ether, which was light. Of these two modes of conceiving and explaining the phenom- ena of light, the Newtonian, or system of emission, as it is usually called, is the most simple and easy of comprehension, and explains adequately all the more common phenomena, though in some particulars defective, and is the one which we shall use. The second, or system of undulations, explains with great precision the most minute of these phenomena, and affords great facility to math- ematical calculations. But for a complete comprehension of this system, extensive mathematical knowledge and familiarity with abstract science is indispensable. All the phenomena which light presents constitute the science of optics. It is divided into two parts: the first, which is called Catoptrics, relates to the phenomena connected with the reflection of light. The second, known by the name of dioptrics, is con- cerned in the phenomena presented by light when it passes through bodies. It was long supposed that light passed instantaneously from one point to another. Rcemer first demonstrated that light requi- red a certain time in passing through space, by showing that it was not instantly transmitted from the satellites of Jupiter. By carefully observing their eclipses, he proved that they remained visible for some time after they should have disappeared behind that planet, and that they did not appear at the opposite side un- til some moments after the time that they must have been disen- gaged from its disc. A great number of accurate observations have demonstrated that light moves at the rate of eighty thou- sand leagues in a second, and requires about 8' 13" to reach us in passing from the sun. Hence, from the immense spaces by which the heavenly bodies are separated from each other, they are nev- SENSE OF VISION--LIGHT. 37 er actually seen at the points at which they appear to us. It has been computed that light probably requires many years to pass to us from the smallest of the fixed stars. It is ascertained that it requires about three years from the nearest of the fixed stars. The velocity of light, assuming that it consists of molecules, may give some idea of the size of these molecules. The momen- tum of a body consists of its mass and velocity combined. The momentum of light is just sufficient to affect the retina, the most delicate and sensible structure of the body. Now if we suppose a molecule of light to be one of the smallest masses that can be cal- culated, its momentum would exceed that of a musket-ball. What, then, must be the mass, seeing they do not injure the retina ! As light moves in right lines, aW cannot traverse certain bod- ies which are called opaque, it necessarily happens that, when such bodies are exposed to a ray of light, that there is a space be- hind which is deprived of light; this is the shadow.*] A ray of light is a series of particles succeeding each other, without interruption, in a right line. The particles which com- pose a ray are separated from each other by considerable inter- vals, relatively to their masses. This may •be shown by making a large number of rays cross each other at any given point, when it will be perceived that the particles do not strike against each other in meeting. Light, in passing from luminous bodies, forms diverging cones, which, ii they meet with no obstacles, are prolonged indefinitely. Natural philosophers have inferred from this, that the intensity of light received from a luminous body in any given spot is in an inverse ratio to the squares of the distances of the surface of the luminous body from which it arises. Those bodies which trans- mit the light are called media. When light meets in its progress certain bodies called opaque, it is turned from a right line, and the direction given to it is modified by the disposition of the sur- faces of those bodies. The change of direction which the light undergoes in this case is called reflection. Certain bodies transmit light, or suffer it to pass through them; for example, glass. These are said to be transparent or diapho- nous. In passing through them, the light undergoes a certain change, called refraction. As the mechanism of the organ of vis- ion, from its structure, depends entirely upon the principles of re- fraction, it will be necessary to stop for a moment, for the purpose of examining the subject The point at which a ray of light enters a medium is called the point of immersion, and that from which it passes out, the point of emergence. If a ray enters perpendicularly the surface of a medium, it passes through the medium preserving its first di- rection ; but if it strikes obliquely to the surface of the medium, it is turned from its course, so that it appears broken at the point of immersion. . The angle of incidence is that contained between the incident * Physique Medicale.—Magendk. 39 FUNCTIONS OF RELATION. ray and a line drawn perpendicularly to the surface of the me- dium from the point of immersion. The angle of refraction is that contained between the line described by the refracted ray and a line perpendicular to the refracting surface at the point of immersion. A ray of light passing from a rarer into a denser medium is refracted towards a perpendicular to the surface of the denser, drawn from the point at which the ray meets the medium; but, on the contrary, in passing from a denser into a rarer, it is re- fracted from the perpendicular. When a ray of light passes from a rarer through a denser medium, the two surfaces of which are parallel, the ray, in passing into the surrounding air, will take a direction parallel to that of the incident ray. [This may be illustrated by the following diagram. Let A B represent a dense medium, as a piece of glass, with air on either side. R, a ray of light striking the surface of glass obliquely at S, the point of immersion. Instead of pursuing its original course along the line R S O, it will be refracted or turned in the direction S T, towards the line S P, which is perpendicular to the surface of A B, the denser medium. When the ray ar- rives at T, passing from the denser into a rarer medium, it will be again refracted or turned, but in an opposite direction, and de- scribe the course T U instead of T V. But if the course of the ray be perpendicular to the surface of the denser, it passes through without undergoing any change in its direction.—Ed.~\ Bodies refract light in proportion to their density* and combus- tibility. Thus, if two bodies be of equal density, but one more combustible than the other, the refractive power of the first will be found greater than that of the second. All diaphonous bodies, at the same time that they refract light, reflect it. In proportion as bodies possess this last quality, they are capable of being used as mirrors. When they have but little density, as, for example, the atmospheric air, they are only visible when they exist in con- siderable volumes. The form of refracting bodies has no influence upon their re- * Density is the relation of weight to volume. If all bodies were of the same volume their relative density might be determined by their weight. volume, SENSE OF VISION--LIGHT. 39 fracting power, but it modifies the disposition of the refracted rays with respect to each other. The perpendiculars at the sur- face of the refracting body approaching or separating from each other, according to the form of the body, the refracted rays must also converge or diverge from each other. When, from the form of a refracting body, the rays are made* to converge, the point where they unite is called the focus of the refracting body. Bod- ies of a lenticular form, or those bodies which are terminated by two segments of spheres, present this phenomenon. A refracting body with parallel surfaces does not change the direction of the rays, but approximates them towards its axis by a sort of trans- port. A refracting body with two convex surfaces, called a lens, does not possess a greater refracting power than a body which is convex on one side and plane on the other, but the point where the rays unite is nearer. [Refracting media, terminated by curved surfaces, produce dif- ferent effects upon light, according to the nature and arrange- ment of the curved surface. In order to collect a pencil of rays proceeding from a distant object accurately to a focus, the dense medium must be of a lenticular form. If we suppose the object to be very remote, the rays composing the pencil must be nearly parallel, as in the following diagram. (Fig. 5.) T Let A B C D represent the rays, and T W the lens. There will be one of these rays, and but one, viz., C I, which strikes the lens perpendicularly, and will, therefore, continue its rectilinear course to R without undergoing any refraction. B and D, situa- ted near the central ray, will undergo a small degree of refrac- tion, the obliquity in the surface of the lens being but slight at this point. But the rays A and E, striking the lens at a point where there is greater obliquity of the surface, will undergo a greater amount of refraction, which is required in order to bring them to the same focus. MNOPQ represent the convex surface of the posterior part of the lens, through which the rays emerge when passing into a rarer medium. According to the same law, this increases the convergence of the rays. Thus, by making the denser medium convex on both sides, both surfaces concur in pro- ducing the desired effect. This is called a double convex lens, and is more strikingly shown in the following diagram. 40 FUNCTIONS OF RELATION. (Fig. 6.) When the rays of light are transmitted through the same me- dium, they proceed in straight lines. Let us imagine a dark chamber into which no light is allowed to enter except by a sin- gle small aperture, as is shown in the following diagram. It is evident that each ray will, in that case, illumine a different part of the wall. Thus, the whole external scene will be faithful- ly represented, though it will be in an inverted position. This in- version of the image is a necessary consequence of the crossing of all the rays at the small aperture through which they are ad- mitted. It must also be a necessary result of limiting the illumi- nation to a single ray, that the image thus formed will be very faint. If the aperture were enlarged, the image, indeed, would be brighter, but more indistinct from the intermixture and mutual interference of adjacent rays. The only mode by which distinct- ness of the image can be obtained is to increase the number of rays. This may be done by means of a double convex lens. If, then, in a dark chamber (as in fig. 7), we enlarge the aper- ture and fit into it a double convex lens, we form a camera ob- scura. In this well-known optical instrument, the images of ex- ternal objects are formed upon a white surface of paper, or a semi-transparent plate of glass. These images must evidently be in an inverted position with respect to the actual objects that they represent. There is a striking analogy between the construction of the camera obscura and the eye. The latter, however, is greatly superior in many respects, particularly in its spherical shape, by which the retina is enabled to receive every portion of the images produced by refraction, which are themselves curved. ENSE OF VISION--LIGHT. 41 Whereas, if received on a plane surface, as in the camera, a con- siderable portion of the image would be indistinct.—Ed.~\ The study of refraction makes us acquainted with an extreme- ly important fact: it teaches us that a beam of light is composed of an infinite number of differently-coloured rays, which are dif- ferently refrangible ; i. e., if the medium and angle of incidence be the same, the refraction of the rays differ with their colour. If, in a room previously darkened, we allow a beam of light to pass through a small aperture, so that it will traverse a prism of glass, or any other refracting body, the surfaces of which are not parallel, and if this be received on any plain surface, as, for exam- ple, a sheet of paper, it will be seen that the beam occupies a con- siderably larger space than the size of the aperture, of an oblong form ; and, instead of producing a white image, a number of dif- ferent colours will be observed, which run insensibly into each other, and among these may be distinguished the seven following colours, viz., red, orange, yellow, green, blue, indigo, and violet. Neither of these colours are capable of being decomposed; they are together called the solar spectrum. Light is not, therefore, homogeneous, but is composed of very differently-coloured rays. On this fact is founded the explanation of the different colours of bodies. A white body reflects light without decomposing it; a black body does not reflect light, but totally absorbs it; coloured bodies decompose light, and reflect it; they absorb some of the rays and reflect others. Thus a body will appear red when the red rays are alone reflected and the rest absorbed, or will ap- pear green when the union of the colours reflected form green. Transparent bodies also appear coloured from the light which they refract, and when seen by refraction, they appear of a col- our different from what they seemed by reflection. If, now, it be inquired why certain bodies reflect one ray and absorb another, it will be replied, that this phenomenon arises from the peculiar arrangement of the particles of which the body is composed. [The seven colours of the prism are evidently, then, the con- stituent parts of the white light; if they are all made to converge upon the same surface by means of seven mirrors, the white light is reproduced. Again, if we unite on one side three of the rays, and on the other side the other four, we obtain two shades which are obviously complements of each other, and which produce white light when united. Newton supposed that the power of refracting media to separ- ate the coloured rays from each other was in proportion to their refractive force. But Dollond discovered that the two properties were not necessarily connected, and that a body might refract less than another and disperse more. This enabled him to pre- serve in a prism, or a compound glass, the power of refraction and destroying that of dispersion of light. This fortunate result is known by the name of achromatism, or privation of colour, be- cause, by the aid of certain combinations, we can prepare lenses which give white images, or, at least, preserve the natural colour 42 FUNCTIONS OF RELATION. of objects. The two substances which compose achromatic glass- es are common glass, without lead, commonly known as flint- glass, or glass containing a large quantity of the oxide of lead, called crown-glass.,*] The discovery of the action of refracting bodies upon light has not been a mere object of curiosity, but has led to the construc- tion of ingenious instruments, by means of which the sphere of human vision has been astonishingly extended. Apparatus of Vision. The apparatus of vision is composed of three distinct parts. The first modifies the light, the second receives the impression of this fluid, and the third transmits this impression to the sensorium. The structure of this organ is extremely delicate. Nature has taken, therefore, great care to place before it various parts, which protect and preserve it in a condition necessary to the free and easy exercise of its functions. The protecting parts are the eyebrows, the eyelids, and the ap- paratus for the secretion and excretion of the tears. The eyebrows are peculiar to man, and are formed, 1. By hairs of various colours. 2. By skin. 3. By sebaceous follicles placed at the root of each hair. 4. By muscles destined to move it, viz., the frontal portion of the occipito-frontalis, the superior edge of the orbicularis palpe- brarum, and the corrugator supercilii. 5. By numerous bloodvessels. 6. By nerves. The eyebrows have various uses. The projections which they form protect the eyes from external violence. The hairs, from their oblique direction, and from the oily substance with which they are covered, prevent the sweat from running into the eye, and irritating the surface of the organ ; they direct it towards the temple and root of the nose. The colour and number of the hairs of the eyebrows have some influence upon their use. These are found to have some relation to the climate. The inhabitants of warm climates generally have them very thick and very black. The inhabitants of cold regions may have them thick, but they are seldom black. The eyebrows guard the eye from the too vivid impression of light, particularly when they are drawn to- gether, as in the act of frowning. The eyelids are two in number in man, and are divided into superior and inferior, or great and small—palpebra major and palpebra minor. The form of the eyelids is accommodated to that of the globe of the eye, so that, when they are brought to- gether, they completely cover the anterior surface of that organ. They do not meet on a level with the transverse diameter of the eye, but considerably below it; this was, therefore, falsely called by Haller aquator oculi. The more extended the opening that * Physique Medicale. SENSE OF VISION. 43 separates the eyelids, the larger the eye appears ; the opinion we form of the size of the eye is often, therefore, very incorrect. The open edge of the eyelids is thick, firm, and furnished with hairs, more or less numerous, which are, generally, of the same colour with the hair of the head. These hairs are placed very near to each other. Those of the superior eyelid form a slight curve upward, but those of the inferior eyelid turn in an oppo- site direction. When they are very numerous and very long, they are considered beautiful; an idea which agrees very well with the utility resulting from them. The eyelashes are covered with an unctuous substance, derived from the small follicles situ- ated in the thickest part of the eyelids, near the roots of the eye- lashes. They have these, in common with the hair, in most parts of the body. Between the line occupied by the eyelashes and the internal surface there is a smooth edge, where the eyelids touch each other. This may be called the margin of the eyelids. The eyelids are composed of a muscle with semicircular fibres, the orbicularis palpebrarum, of a cartilage, of a ligament, the large ligament of the eyelid, of a great number of sebaceous follicles, meibomian glands, and a portion of mucous membrane. All these parts are connected together by cellular membrane, generally loose and fine, and containing no fat. The skin of the eyelids is very fine and semi-transparent; it adapts itself readily to their movements, and presents transverse folds. The muscle of the eyelids, by its contraction, approximates them, or, as we common- ly express it, shuts the eye, at the same time that it presses the eyelids a little upon the globe of the eye. The cartilages of the eye are called tarsi. That of the superi- or is much larger than the inferior; their use is to keep the eye- lids extended, and constantly accommodated to the form of the eye; they also support the eyelashes, afford a suitable situation for the meibomian glands, and serve to protect the eye from external injury. The use of the tarsi, as respects the motion of the eyelids, does not appear indispensable, as they are not found in many animals, the eyelids of which, nevertheless, perform their functions well. The large ligament is nothing more than the cel- lular membrane which passes from the base of the orbit to the su- perior edge of the cartilage of the tarsus. It seems intended to limit the motion by which the eyelids approach each other. The cellular tissue of the eyelids is extremely fine and delicate, and contains no fat, but is filled with a very thin serum, which in some cases has a greater degree of consistence, and accumulates in the cells of this tissue ; when this is the case, the eyelids become distended, and of a bluish colour. This colour and swelling of the eyelids is frequently observed after excesses of every kind, af- ter severe diseases, during convalescence, and in women during menstruation, &c. The fineness and laxity of the cellular mem- brane of the eyelids, and the absence of fat from its cells, are ne- cessary for their free motion. The internal surface of the eyelid is covered by a mucous membrane. Besides the parts already 44 FUNCTIONS OF RELATION. mentioned, the superior eyelid has a muscle proper to it: this is called the elevator palpebrae superioris. The eyelids cover the eye during sleep, and preserve it from the contact of foreign bodies which float about in the atmosphere; they preserve it from blows by their instantaneously closing ; by habitually closing at nearly regular intervals, they prevent any bad effect from the long-continued contact of the air, and have likewise the power of moderating the effect of a too brilliant light. By closing together, they only suffer such a quantity of light to pass as may be necessary for vision, but not sufficient to injure the eye. On the other hand, when the light is weak, we separate the eyelids widely, so as to permit the largest quantity of light possible to penetrate to the interior of the eye. When the eyelids are near, the eyelashes form a sort of grate, which only suffers a certain quantity of light to pass at a time. When the eyelashes are moist, the small drops which cover their surfaces decompose the light in the manner of a prism, and, at the point where the light passes, cause it to appear variegated like the rainbow. The eyelashes, by dividing the light which penetrates into the eye into pencils, cause ignited bodies to appear, during the night, as if they were surrounded by luminous rays. These appearances vanish as soon as the eyelid is thrown back, or another direction given to the eyelashes. It is supposed that the eyelashes preserve the eye from the atoms of dust which are floating in the air. Vision is always more or less affected in those persons who have lost the eyelashes. The compound follicles placed in the thickest part of the tarsi are called the meibomian glands. They are very numerous. There are from thirty to thirty-six in the upper eyelids, and from twenty-four to thirty in the lower. In each compound follicle there exists a central duct, about which are placed the simple follicles, and into which they pour the matter they secrete. This duct is always filled with the matter, which, in its ordinary state, is called the meibomian humour, but when it is thick and dry, is called gum. After sleep, a certain quantity of this is al- ways found accumulated in the inner angle of the eye and on the margin of the eyelids. This matter seems to be of an unctuous nature, but particular researches have induced me to believe that it is essentially albuminous. Each central duct has an opening, hardly visible, on the internal surface of the eyelid, very near to the margin. These openings are close to each other, and range along the whole length of the margin. The meibomian humour passes out through these openings when we compress the eyelids tightly; as they experience a sensible pressure on closing the eyelid, it is probable that this pressure contributes to the excretion of the hu- mour. The principal use of this humour seems to be to diminish the friction of the eyelids on the globe of the eye. As the upper eyelid has a greater extent of motion, and will, of course, produce more friction, it requires a greater number of these follicles. SENSE OF VISION. 45 Apparatus for the Tears. The office of guarding the eye, and preserving it in a condition necessary for the performance of its functions, is not confined ex- clusively to the eyebrows or eyelids. There is likewise to be reckoned among the tutamina oculi a small secretory apparatus, of which the mechanism is very curious, and the utility very great. This is the secretory apparatus of the tears. It is composed of the lachrymal gland, the excretory ducts, the caruncula lachryma- lis, the lachrymal ducts, and the nasal duct. In the small fossa, formed at the anterior and outer part of the arch of the orbit, is placed the lachrymal gland ; it is small, and serves to secrete the tears. This gland was known to the an- cients, and was called by them the glandula superior innominata, in opposition to the caruncula lachrymalis, which they called the glandula innominata inferior. They attributed the formation of tears partly to the caruncula, and partly to a gland that does not exist in man, but is found in certain animals: this is the gland of Harderus. There are six or seven excretory ducts of the lachrymal glands. They arise from the small glandular bodies that together form this gland. After having passed through the substance of the gland, they enter the conjunctiva, and pierce this membrane very near the cartilage of the upper eyelid, towards^its external extrem- ity. They may be rendered visible by blowing into them, or by raising the upper eyelid, and compressing the gland, when the tears will be made to pass out of the orifices of the ducts. This may likewise be done by macerating them in water tinged with blood, or by injecting them with mercury. The tears are poured through these orifices upon the surface of the conjunctiva. At the internal angle of the eye is seen a small, projecting, red body, which, when it is of a bright colour, indicates health and vigour; when it is pale, debility and disease : this is the carun- cula lachrymalis. This small body is composed of seven or eight follicles, ranged in a semicircular line, the convexity within; they have each an opening on the surface of the caruncula lachrymalis, and contain a small hair. These openings are so disposed that they complete, together with the meibomian glands, a circle em- bracing the whole anterior part of the eye when the lids are closed. At the point where the eyelids leave the globe of the eye to in- clude the caruncula, on the internal surface, near the open edge, on each lid, is seen a small ppening: these are the puncta lachry- malia, or external orifices of the lachrymal ducts. The puncta are always open, with their orifices directed towards the eye. It has been supposed that they possess a contractile power, which may be shown by touching their extremity with a pointed instru- ment. Though I have often endeavoured, with great care, to dis- tinguish these contractions, yet I have never succeeded. One cir- cumstance should be mentioned which is extremely apt to de- ceive us. When we unsuccessfully attempt to introduce the style, 46 FUNCTIONS OF RELATION. the mucous membrane, which covers the puncta, becomes soon irritated and swelled, as would occur from the same violence at any other part, when the opening will, of course, be diminished. It is necessary to distinguish this phenomenon from a contraction of the part. The lachrymal ducts arise from the puncta, and terminate in a canal extending from the inner canthus of the eye to the nasal fos- sae. The lachrymal ducts are very narrow, scarcely suffering a hog's bristle to pass. They are from three to four lines in length, and are placed in the thickest part of the eyelid, between the or- bicularis muscle and the conjunctiva. They terminate sometimes singly, and sometimes together, in the superior part of the nasal canal. The canal extending from the inner angle of the eye to the in- ferior passage of the nasal fossae has been improperly divided by anatomists in two parts. This canal is throughout of the same dimensions; there is nothing, therefore, to justify the distinction that has been made, in calling the upper part the lachrymal sac, and the lower the nasal duct. This canal is always formed by the mucous membrane of the nasal fossae, which covers the osseus duct, passes along the posterior edge of the projecting apophysis of the maxillary bone, and the anterior part of the os unguis. Its use is to conduct the tears into the nasal fossae. (Fig. 8.) ) [L is the lachrymal gland, situated above the eye, in a hollow of the orbit. D the ducts proceeding from it, and opening upon the inner side of the upper eyelid at E. The eyelids, in closing, meet first at the outer angle, the junction proceeding towards the inner angle, until the contact is complete. By this means the tears are carried in that direction, and accumulated at the inner angle. They are conveyed off by two ducts, the orifices of which, P P, are the puncta lachrymalia. C is the lachrymal caruncle. The two ducts unite, and open into the lachrymal sac S, situated at the upper part of the side of the nose, and which terminates below at N, in the cavity of the nostrils.] SENSE OF VISION. 47 The membrana conjunctiva may be ranked among those or- gans which constitute the apparatus for the tears. This is a mu- cous membrane, which covers the posterior surface of the eyelids, and is reflected over the anterior surface of the globe of the eye. It is more extensive than the part it covers, and is therefore very favourable to the motion of the eyelids and the eye. The loose manner in which it is attached to the eyelids and the tunica scle- rotica greatly facilitates their movements. Whether the conjunc- tiva passes over the transparent cornea or stops at the circumfe- rence of this portion of the eye, and is then connected with a dis- tinct membrane which covers it, is not yet perfectly decided. The general opinion is, that it covers the cornea; but M. Ribes, a very distinguished and expert anatomist, contends that the cor- nea is covered by a peculiar membrane, united to the conjunctiva at its circumference, without being a continuation of it. The con- junctiva protects the anterior parts of the eye; it secretes a fluid which mixes with the tears, and appears to have the same use; it likewise possesses the power of absorbing,* and, as it is very smooth and moist, it greatly facilitates the motions of the eye; lastly, it is the part in contact with the air when it is not covered by the tears, of which we are now about to speak.f Secretion of the Tears, and their Uses. This is not the place where we intend to enter into a minute description of the secretion of the tears, and in what it resembles or differs from other secretions. It is sufficient here to remark, that the lachrymal gland forms them through the influence of the fifth pair of nerves, J and that they are poured out through its ex- cretory ducts, of which we have spoken, upon the conjunctiva, at the outer and superior part of the eye. We shall next inquire how they proceed when they have arrived at this part. They are poured out, we would observe in the first place, as well du- ring sleep as when we are awake. In this last state, the eyelids opening and shutting alternately, the conjunctiva is exposed to the contact of the air, and the eye moves continually, neither of which happens during sleep. Physiologists have supposed that the tears run along a triangu- lar canal, formed to conduct them towards the inner canthus of the eye, where they are absorbed by the puncta. This canal, say they, is formed, first, by the edge of the eyelids, the surfaces * We may poison an animal by applying to the conjunctiva poisonous substances. For this reason we cannot agree with Mr. Adams, the celebrated London oculist, who thinks that the belladonna may be continually applied to the eye without inconvenience. t I have noticed a remarkable fact in these experiments.—(See Journ. de Phys., t. iv., 1824.) The section of the opthalmic nerve is constantly followed in animals by a violent in- flammation, with abundant suppuration of the conjunctiva, and subsequently, ulceration of the comea, and discharge of the humour; but the surface of the eye remains completely insensible. Those authors who venture to explain morbid phenomena should combine such facts with their doctrines ; violent inflammation, with complete loss of sensibility. % I have repeatedly touched the lachrymal nerve with the point of a fine needle, to which I have afterward applied galvanism, and have uniformly observed that the moment the nerve was touched by the point of the needle, the tears flowed as abundantly as if some irritating substance was introduced under the eyelids in contact with the conjunctiva, or perhaps even more so. 48 FUNCTIONS OF RELATION. of which being convex, only touch at one point; and, second, by the anterior face of the eye, which completes the triangular cavi- ty. This canal has its external extremity more elevated than its internal. This arrangement, joined with the action of the orbicu- laris muscle, the most fixed point of which is attached to the pro- jecting apophysis of the os maxillare, directs the tears towards the puncta lachrymalia. But this explanation is defective; the eyelids have not a con- vex edge at the part where they come in contact with each other, but have plain margins ; no such canal, therefore, can exist. In- deed, when we examine the eyelids at their posterior surface, when they are shut, it is scarcely possible to distinguish the line where they come in contact. But even admitting the existence of such a canal, it could serve as a duct for the tears only during sleep, and it would still remain necessary to show how they are disposed of when we are awake. During sleep, and at all times when the eyelids are closed, the tears spread, by degrees, over the whole surface, both of the ocular and palpebral conjunctiva. They will, of course, pass in the largest quantities to those points where they meet with the least resistance. The direction where the resistance is least is the part where the conjunctiva passes from the eye to the eyelids. In this direction they arrive more easily at the puncta lachrymalia. The tears which are spread over the conjunctiva must become mixed with the secreted fluids of this membrane, and be absorbed together. But when we are awake, they do not pass off in this way. That portion of the conjunctiva which is in contact with the air allows the tears which cover it to evaporate, and it would become dry if the moisture were not renewed by the action of winking. This seems to be the principal use of winking. The tears, which thus constantly cover that part of the conjunctiva exposed to the air, give to the eye its polish and brilliancy. The increase or diminution of the tears influences very much the expression of the eyes. During the excitement of the pas- sions this is very apparent. In the ordinary state of the secretion of the tears, they do not tend, in any way, to run over the inferior eyelid. I know not how the idea has arisen that the meibomian humour is intended to prevent this, except from the supposed anal- ogy of oily substances, which, when placed on the edge of a ves- sel, prevent aqueous fluids from running over, even when they rise somewhat above its level. But I doubt if this humour can have such an effect, as it is soluble in the tears. The tears, which do not evaporate, or are not absorbed by the conjunctiva, are received into the puncta, and conveyed through the nasal duct to the nose. What the power is by which this is effected is not certainly known. It has been explained on the principle of a syphon, capillary attraction, vital properties, &c. That of capillary attraction is, perhaps, the most probable. The absorption of the tears by the puncta is not very apparent, except when they are very abundant. SENSE OF VISION. 49 Globe of the Eye. The apparatus of vision is composed of the eye and optic nerve. The situation of the eye, at the highest part of the body; the ca- pacity in man of discerning, at the same time, with both eyes the same object; the oblique direction of the base of the orbit; the protection afforded to the eye by this cavity from external inju- ry ; the great abundance of adipose substance and cellular mem- brane, which form an elastic cushion at the bottom of the orbit, &c, are curious and interesting circumstances, which should not be neglected, but which we can only mention in passing. The eye is composed of many different parts, which perform very different offices in the function of vision. They may be di- vided into the refracting and non-refracting parts of the eye. The refracting parts are, the transparent cornea, which is con- vex on one side and concave on the other. In its form, transpa- rency, and mode of insertion, it greatly resembles the crystal of a watch. The aqueous humour, which fills the chambers of the eye, is not a pure watery fluid, as its name implies, but is chiefly composed of water, with a little albumen.* The crystalline humour has been compared to a lens. The comparison is correct as far as the form is concerned, but is very defective as respects its structure. The crystalline humour is composed of concentric laminae, which increase in density as you approach the centre, but differ in refrangibility; and it is envel- oped in a membrane, which we know, from experience, to be ex- tremely important. On the other hand, we know that a lens is homogeneous throughout, and that its density and refrangibility in all its parts are the same. It has been always remarked that the convexity of the anterior surface of the crystalline humour differs considerably from its posterior surface. The last is a part of a sphere, the diameter of which is much less than that to which the anterior surface would belong. It has been generally believ- ed that this humour was composed chiefly of albumen; but, from an analysis lately made by M. Berzelius, it appears that it con- tains none. It is formed almost entirely of water, and a particu- lar substance, which has a greater analogy, in its chemical prop- erties, with the colouring matter of the blood than with anything else. Behind the crystalline is found the vitreous humour, which is so called from its supposed resemblance to melted glass.f Each of the parts which we have pointed out are enveloped in an extremely delicate, transparent membrane. Thus, before the cornea is the conjunctiva, behind it the membrane of the aqueous humour, which covers all the anterior chamber of the eye, i. e., * According to M. Berzelius, it is composed of water, 98.10; a little albumen; muriates and lactates, 1.15; soda, with a substance only soluble in water, 0.75. t According to M. Berzelius, it contains water, 98.40; albumen, 0.16; muriates and lac- tates. 1.42 ; soda, with animal matter soluble in water only, 0.02; total, 100.0. G 50 FUNCTIONS OF RELATION. the anterior surface of the iris, and the posterior face of the cor- nea. The crystalline is enveloped in its capsule, which adheres, at its circumference, to the membrane which encloses the vitreous humour. In passing from its circumference over its anterior and posterior surfaces, it leaves between the two lamina an interval, called the canal of Petit. It has been generally supposed that this canal does not communicate with the chamber of the eye; but M. Jacobson asserts that it presents a great number of small openings, by means of which, according to him, the aqueous hu- mour can enter in or go out; but I have carefully sought,in vain, to find these openings. The vitreous humour is surrounded by a membrane called mem- brana hyaloidea. This membrane not only surrounds the humour, but it is divided into innumerable cells, which are filled by it. It is not necessary to say anything of the arrangement of these cells, as this is not of importance in investigating the uses of the vitre- ous humour. The eye is not only composed of refracting parts, but likewise. of others, which have each a peculiar destination. The tunica sclerotica is a strong fibrous membrane, which con- stitutes the external coat of the eye. Its evident use is to protect the internal parts of the organ; it likewise serves as a place of insertion to the muscles which move the eye. The choroid coat abounds with bloodvessels and nerves, and is distinctly formed of two laminae. It is covered with a black substance, which evidently performs an important part in the function of vision. The iris is a small circular part, which may be seen moving behind the transparent cornea. It is of different colours in dif- ferent individuals, and is pierced in its centre by an opening call- ed the pupil, which enlarges and contracts according to circum- stances, which we shall hereafter point out. The iris adheres anteriorly, at its curcumference, to the sclerotic coat by a peculiar cellular tissue, which is called the ciliary ligament. The poste- rior face of the iris is covered by a black substance in considera- ble abundance. Behind the circumference of the iris are a num- ber of white, radiated lines, which would unite at the centre of the iris if they were prolonged: these are the ciliary processes. Anatomists are not yet agreed as to the nature and uses of these bodies. Some consider them nervous, others muscular, and oth- ers, again, glandular or vascular. The truth is, at present it is not easy to decide which of these opinions is most probable; and we shall, by-and-by, see that their use is equally unknown. The colour of the iris depends on that of its tissue, which is variable, and that of its posterior surface, which is of a deep black, and affects the appearance of its anterior face. In blue eyes, for example, the tissue of the iris is nearly white, but the deep black, on the posterior part, modifies this, and determines the colour of the eyes. Anatomists vary in their opinions of the nature of the tissue of the iris. Some consider it similar to that of the choroid SENSE OF VISION. 51 coat; that is, they suppose it to consist chiefly of vessels and nerves ; others think they can distinguish a great number of mus- cular fibres; it has by some been thought a tissue sui generis; and by others confounded with the erectile tissue. M. Edwards thinks that he can demonstrate the iris to be formed of four dis- tinct laminae, of which two are a continuation of the laminae of the choroid coat, a third pertains to the membrane of the aque- ous humour, and a fourth that forms the peculiar tissue of the iris. It appears from the latest researches respecting the anatomy of the iris, that this membrane is muscular, and that it is composed of two planes of fibres: an exterior, radiated, which dilates the pupil; the other circular and concentric, which closes the pupil. The external circular fibres appear to be supported by a kind of ring which forms each radiated fibre, and in which they glide in the movement of contraction and closing the pupil. The iris re- ceives bloodvessels and the ciliary nerves ; the latter are derived from two sources: 1st, the opthalmic ganglion; 2d, the nasal nerve of the fifth pair. Between tlje membrana hyaloidea and the choroid coat there is a membrane chiefly composed of nerves. This is known by the name of retina; it is nearly transparent, with a very small degree of opacity, of a slight filaceous tint, and appears to be formed by the expansion of the optic nerve. M. Ribes, however, thinks differently; he supposes it is formed of a distinct mem- brane, upon which the optic nerve is very freely distributed. He thus establishes an analogy between the retina and the other mem- branes. There is upon the back part of the retina, about two lines from the optic nerve, a yellow spot, and at the side of this there are several folds. But these appearances are only found in man, and some species of apes. The eye receives a large number of bloodvessels, and many nerves, the greater part of which come from the opthalmic ganglion. The Optic Nerve. This is the medium of communication between the eye and the brain. It does not arise from the thalamus nervi optici, as many anatomists have thought, but it derives its origin, 1st, from the an- terior pair of those tubercles called the quadrugemini; 2d, from the corpus geniculatum externum, an eminence found before, and a little to the outer side of, these tubercles; 3d, from the laminae of cineritious substance, placed before the meeting of the optic nerves and mamillary eminences, and which is known by the name tuber cinereum. The two optic nerves approach each other, and seem to be blended together near the superior part of the sphenoid bone. The most careful researches have been made for the purpose of determining whether they decussate or are in con- tact, or if they really intermix with each other; anatomy has not yet settled this question, but pathology furnishes proofs of all these opinions. Thus, when the right eye has been long atrophied, the optic nerve of the same side has been known to become so 52 FUNCTIONS OF RELATION. through its whole extent. In another case, where the right eye was atrophied, the anterior portion of the same side was found in an evident state of disease, and the posterior portion of the left side to present the same appearance. Some have thought that the crossing of the optic nerves in fishes removed every doubt on the subject; but this can only be justly considered as amountmg to a probability. I divided, in a rabbit, the right optic nerve behind the crossing; the consequence was, loss of vision of the left eye. I divided the left nerve; vision was completely abolished. In another animal, I divided, into two equal portions, the crossing over the median line ; the animal was immediately deprived of sight. The cross- ing is then total, and not partial,* as was supposed by the learned Woolaston. Here, as in many other instances, physiological ex- periment speaks in language clear and positive, when minute an- atomy can only raise doubts. The optic nerve is not formed of a fibrous envelope and of a central pulp, as the ancients believed, but it is composed of very fine filaments, placed at the side of each other, and conimunica- ting with each other, like other nerves. This arrangement is very evident in that portion of the nerve which extends from the sella turcica to the eye. [The figure beneath represents a hori- zontal section of the globe of the eye, after Home. (Fig. 9.) S represents the sclerotica, the external coat. It is perforated by the optic nerve at O, which is expanded into the retina R. * In birds the crossing is proved in another manner. I emptied the eye of a pigeon; fifteen days afterward, I lound, on examination, that the nervous matter had disappeared, and the nerve atrophied before the crossing, on the side of the emptied eye and on the op- posite side behind the crossing. The atrophy extended to the optic tubercle, the point where the optic nerve takes its origin. SENSE OF VISION. 53 The internal or choroid coat is indicated at X, and is covered by the pigmentum nigrum. Within the pigmentum nigrum, and al- most in contact with it, the retina R is expanded. Three fourths of the globe of the eye are filled by the vitreous humour, marked V. The crystalline humour, L, is a double convex lens. It oc- cupies the anterior part of the globe, immediately in front of the vitreous humour, which is hollowed out to receive it. The space which intervenes between the lens and the inner surface of the cornea, C, is filled with the aqueous humour A. This space is di- vided into the anterior and posterior chamber by the iris I. The central perforation of the iris, called the pupil, is indicated by P. Q, is the ciliary ligament. The central part of the retina being endowed with the highest degree of sensibility, it is necessary that the images should be made to fall upon this part, and, consequently, that the eye should be capable of having its axis directed to those objects, wherever they may be situated. Hence muscles are provided within the orbit for moving the globes of the eye. (Fig. 10.) Muscles of the Eye. Four of these muscles proceed in a straight course, and are called recti. They arise from the bottom of the orbit and the margin of the aperture through which the optic nerve passes, and are inserted by a broad tendinous expansion into the anterior part of the sclerotic coat. Three of them are seen in the diagram, and marked ABC. The margin of the fourth is seen behind and above B. A draws the eye upward, C downward; B and its an- tagonist move it laterally. There are also two other muscles, which are called oblique, S and I, which give the globe some ro- tation upon its axis. When they act in conjunction, they draw the eye anteriorly, and act antagonistically to the recti muscles. The superior oblique muscle S is remarkable for the manner in which its tendon passes through a sort of cartilaginous pulley, P, in the margin of the orbit, and then turns back to be inserted in the globe of the eye. Thus the action of this muscle produces a motion in exactly the reverse direction in which its fibres con- tract. Of the Mechanism of Vision. Considering the visual apparatus in a physical point of view, we may regard the transparent cornea, aqueous humour, and the crystalline as a compound lens, the different parts of which pos- 54 FUNCTIONS OF RELATION. sess different refractive properties, inasmuch as they produce nat- ural achromatism. The general cavity of the eye may be^re- garded as a dark chamber, the choroid being lined with biacn 10 prevent the effects of any scattered rays of light upon the image, while the retina presents a surface on which the images are paint- ed; not, however, as in the camera obscura, to be seen by the eyes of others, but to be perceived by the retina itself, and to be transmitted to the brain by the optic nerve. The ins represents ■ a diaphragm destined to limit the field of the lens, to avoid the effects of aberration of sphericity, and only to permit such a quan- tity of light to penetrate into the eye as will be necessary to paint the object distinctly, without wounding the retina.] To facilitate the explanation of the manner in which the light enters the eye, let us suppose a single luminous cone passing through the antero-posterior axis of the eye. We perceive at once that there is no other light but that which falls upon the cornea that can assist in vision. That which falls upon the white of the eye, the eyelashes, or the eyelids, can evidently contribute nothing to this effect. It is absorbed or reflected from the differ- ent parts, according to their colour. The cornea itself does not receive light through its whole extent, for it is, generally, partly covered above and below by the edges of the eyelids. Uses of the Cornea. The convexo-concave form of the cornea indicates the influ- ence which it must exert upon the light that enters the eye. It converges the rays in proportion to its greater refractive power than that of the air. Thus the cornea contributes powerfully to the refraction of the eye; in other words, it increases the intensi- ty of the light that penetrates into the anterior chamber of the eye. The cornea being very polished at its surface, the light which arrives there is partly reflected, and contributes to give brilliancy to the eye. This reflected light produces the images formed be- hind the cornea, which thus performs the office of a convex mir- ror.* Uses of the Aqueous Humour. In traversing the cornea, the rays of light have passed from a rarer into a denser medium, consequently they are drawn towards the perpendicular. If they then passed out into the air, instead of entering the anterior chamber of the eye, they would be refracted from the perpendicular, which they had before approached, and, of course, would return to their first degree of divergence. But they enter into the aqueous humour of the eye, a denser medium than the atmosphere, and are, therefore, less refracted from the perpendicular, and, of course, diverge less, than if they had re- turned into the air. * I have ascertained, from experiment, that the physical properties of the cornea depend upon the integrity of the fifth pair of nerves. This membrane becomes opaque, and ulcer- ates after the section of this nerve.—(See Nutrition.) SENSE OF VISION. 55 Of all the light entering into the anterior chamber of the eye, that which passes through the pupil alone assists in performing the function of vision. All that falls upon the iris is reflected through the cornea, and enables us to distinguish the colour of the iris. The light does not undergo any new modification in passing through the posterior chamber of the eye, as the medium is still the same. Uses of the Crystalline Humour. In passing through the crystalline humour the light under- goes a new modification, which is most important in the function of vision. Philosophers compare the action of this body to that of a lens, the use of which is to collect together the rays of light upon a certain part of the retina. But, admitting that the crys- talline possesses all the properties of a lens, it could not fulfil the functions, or, at least, one could not compare the effects to that •of a lens used in the air, as its refractive power is nearly the same as that of the aqueous and vitreous humour.*- All that can be positively said on the subject is, that the crystalline humour must increase the intensity of the light which it directs to the bottom 'of the eye in a much greater degree, from the circumstance of the posterior being more convex than the anterior surface. It taay likewise be added, that the light which passes near the cir- cumference of the crystalline humour is probably refracted dif- ferently from that which passes through the centre, f Of conse- quence, the dilatation or contraction of the pupil must have an in- fluence upon the mechanism of vision, which appears to deserve the attention of philosophers. But the crystalline does not produce upon vision the influence long attributed to it, for the function remains after its removal by the operation of cataract. There is another strong proof of this. -An artificial eye, made of a globe of glass, over which is fitted a Section of another smaller sphere, and which is filled with water to represent the three humours, acts like a true eye, for it forms images on the bottom. All the light that strikes on the anterior surface of the crystal- line does not pass into the vitreous humour, but is partly reflected. A part of this reflected light returns through the aqueous humour and cornea, and contributes to form the brilliant appearance of the eye; another part strikes upon the posterior surface of the iris, and is absorbed by the black matter which is found there. This appears to be indispensable to distinctness of vision. In AlbinoeS, ^ Messrs. Brewster and Gordon have given the following results as the refractive pow- ers of the humours of the eye: Water being........1.3358 Aqueous humour ....... 1.3365 Vitreous humour.......1.3394 Exterior lamin» of the crystalline .... 1.3767 Central part of the crystalline.....1.3990 —(See Brewster's Journal, vol. i., p. 49.) t The structure of the crystalline may have the effect to correct the aberration of sphe- ricity which the common lens produces. 56 FUNCTIONS OF RELATION. both in man and the inferior animals, in whom both the ins and choroid are destitute of black matter, the vision is always more or less imperfect.* Uses of the Vitreous Humour. The vitreous humour possesses a somewhat less degree of re- fracting power than the crystalline; of consequence, the rays of light which, after having traversed the crystalline, penetrate into the vitreous humour, are drawn from the perpendicular at the point of contact. Its use, then, as respects the direction of the rays in the eye, is to increase their convergency. It may, perhaps, be said that nature might have arrived at the same result by increasing the refractive power of the crystalline humour. But the presence of the vitreous humour in the eye has another and more impor- tant use; it is to allow a sufficient extent of expansion of the re- tina, and thus greatly to extend the field of vision. M. Lehot, an ingenious and learned natural philosopher, in a se- ries of memoirs on vision, has suggested a singular use of the vit- reous humour. He believes that the walls of the hyaloid cells are the places of sensibility to light in the eye, and that the images are not simple surfaces, but figures. But we must confess that his proofs are far from being satisfactory. What we have thus said of a cone of light passing from a point placed in a prolongation of the antero-posterior axis of the eye, will apply with equal truth to cones passing from every other point towards the eye, with only this difference ; that, in the first case, the rays tend to unite at the centre of the retina, while in the other instance they have a tendency to unite at some other point, according to the direction from which they proceed. Thus those which pass from below upward unite at the superior part of the retina, and those which come from above unite at the in- ferior part of this membrane. The rays of light thus form, at the bottom of the eye, an exact representation of each of the objects which are placed before it, but with this difference, that the im- ages will have a position the reverse of the objects they repre- sent. Different methods have been had recourse to to establish this point. For a long time experiments were made with eyes artifi- cially constructed. Glass was made to represent the transparent cornea and crystalline humour, and water the aqueous and vitre- ous humour. Another mode was generally employed before the publication of my memoir " On the Images formed at the Bottom of the Eye." It consisted in placing in an aperture of the window- shutter of a darkened room the eye of some animal, as, for exam- * Many facts do not agree with this explanation. Most animals remarkable for the ex- cellence ot their vision, especially at night, as cats, foxes, horses, many varieties of dogs, and certain hsh, have the choroid, and even the posterior face of the iris, of a blue, yellow, or green colour, more or less bright. They reflect the light, like those of cats, in the dark. Thus the bottom of the eyes of these animals is a concave mirror. From the theory of vision, it is not easy to understand how it happens that this brilliancy of the choroid should not injure the function. If, m the construction of our telescopes, we neglected to blacken the internal walls of the tubes, great inconvenience would result. SENSE OF VISION. 57 pie, that of an, ox or sheep, having first carefully removed the posterior part of the sclerotica. There could then be seen, very distinctly, upon the retina, the images of objects placed in such a manner as to transmit the rays through the pupil. I had recourse to a much more convenient method for accom- plishing this purpose. I took the eyes of rabbits, pigeons, small dogs, or ducks, in which the choroid and sclerotic coats are near- ly transparent; I then removed carefully the fat and muscles, and by directing the transparent cornea towards brilliant objects, I saw distinctly the images of those objects formed upon the reti- na. This process was known to Malpighi and Haller; the only circumstance peculiar to myself in this respect consists in my having selected for this purpose white rabbits, white pigeons, and white mice ; the eyes of Albinoes would probably be found equally good. These will be found much the most favourable to the suc- cess of this experiment. The sclerotic coat is thin, and almost transparent; the choroid is equally thin, and as soon as the ani- mal is dead, the blood which coloured it disappears, and ceases to offer any perceptible obstacle to the passage of the light. The ease and distinctness with which we are thus enabled to perceive the images, suggested to me the idea of making some experiments, which might confirm or invalidate the commonly-re- ceived theory of the mechanism of vision. If we make a small opening in the transparent cornea, and al- low a small portion of the aqueous humour to escape, the distinct- ness of the image becomes lost. The same thing takes place when we suffer a portion of the vitreous humour to escape by a punc- ture through the sclerotica, which shows that the proportions of the aqueous and vitreous humours are such as to be necessary to perfect vision. I have likewise endeavoured to determine the laws of the dimensions of the image relatively to the distance of the object, and I have found that the size of the image is percep- tibly proportional to the distances. M. Biot had the politeness to confirm with me this result, which is likewise conformable to that given by Le Cat, in his " Treatise on Sensations." This author employed artificial eyes in his experiments. One thing appeared to me worthy of remark in these experi- ments. In varying the size of the image by moving the object near or to a distance, there was no difference observable in its distinctness. But when a portion of the vitreous humour was removed, the distinctness was manifestly impaired. I made a small opening at the circumference of the cornea, near its junction with the sclerotic coat, and evacuated all the aqueous humour through this aperture. On presenting the cornea towards a lighted candle, the image appeared to me, other things being equal, to occupy a much larger space than before. The image was evidently less distinct, and formed by a light much less in- tense than that of the same body seen in the other eye of the same animal, that I had placed in a similar situation with respect to the candle, but which I had preserved whole, for the purpose 58 FUNCTIONS OF RELATION. of making the comparison. This experiment agrees with what we have before said of the use of the aqueous humour in the mechanism of vision. The same effect will be produced by removing the cornea. When this is done by a circular incision, made at the point where it unites with the sclerotic coat, the image will not appear to change its dimensions, but the light which forms it loses very sensibly its intensity. We have before remarked that the size of the open- ing of the pupil probably influences, to a considerable degree, the mechanism of vision. After having removed the cornea, it is easy to enlarge the pupil by a circular incision made into the tis- sue of the iris ; the image in this case becomes enlarged. As the use of the crystalline humour is to increase the brillian- cy and distinctness of the image, diminishing, at the same time, its size, we ought to expect that the absence of this body would produce a reverse effect. When we extract or depress this hu- mour, by a process similar to the operation for cataract, the im- age is always formed at the bottom of the eye, but it is consider- ably increased in size. It becomes at least four times larger than that produced in the entire eye, under the same circumstances. The image is likewise very indefinite, and the light produced very weak. Take away from the same eye the aqueous and crystal- line humours, and the transparent cornea, and leave nothing, of all the media of the eye, but the capsule of the crystalline lens and the vitreous humour, and it will be found that there is no longer any image formed upon the retina. The light still passes very freely, but it no longer affects a particular form, in relation to that from which it emanates. The greater part of these results agree very well with the the- ory of vision'generally admitted at the present day. There is, however, one point in which they differ essentially; this is, re- specting the distinctness of the image. From theory we are led to infer, in order that the image may be distinct, that it is neces- sary that the form of the eye should vary, or that the crystalline humour should be carried backward or forward, according to the distance of the object. These changes, which have been as- sumed actually to take place, have, by turns, been attributed to the compression of the globe of the eye by the recti and oblique muscles which move it, to the contraction of the crystalline hu- mour, or to the action of the ciliary processes. Of late, M. Jacob- son has asserted that this effect was produced by the aqueous humour entering or passing out of the canal of Petit. Now ex- perience contradicts this theory, and, of course, all these explana- tions fall to the ground. T ill It would be very incorrect, however, to assert that everything took place in the eye of the living precisely as it does in that of the dead animal. There is this essential difference, that in the living animal the pupil dilates or contracts according to the in- tensity of the light, and, perhaps, according to the distances of objects. SENSE OF VISION. 59 Motions of the Iris. The circular opening in the centre of the iris, or the pupil, un- dergoes great variations in its dimensions. Sometimes it is scarce- ly visible, at others as large as the cornea, the iris seeming to have disappeared. The circumstances which accompany the motions of the iris are, 1st. The different degrees of the intensity of the light; the greater the light, the more the pupil is contracted. When a solar ray enters the eye, the pupil immediately closes; but if we are placed in an obscure light, the pupil becomes dilated. 2d. The nearer an object on which we are looking is placed to the eye, the more the opening of the iris is narrowed. Experi- ments on this point are delicate, for it is necessary carefully to distinguish that which depends on the variations of intensity of the light from that which is the effect of the distance of the ob- ject. This difficulty is the greater, as all the changes of distance are necessarily accompanied with changes in the intensity of the %ht ... . 3d. The will has a very limited influence upon the actions of the pupil. This, however, is very slight compared with that pro- duced by light in different degrees of intensity. The attention we give and the effort we make to see small ob- jects, cause contraction of the pupil. I satisfied myself of this in the following manner. I selected an individual whose pupil pos- sessed great mobility, and there is a great difference in this re- spect. Having placed before him a sheet of paper, in a conveni- ent position as regarded the eye and the light, and observed the state of the pupil, I then requested the person to endeavour to read some small characters traced upon it, without moving his head or his eyes. Immediately the pupil contracted, and remain- ed so while he made the effort. M. Mille, a young Polish physi- ologist of great promise, has repeated this experiment in a more rigorous form: his results agree perfectly with mine. The superior edge of the pupil of the horse is garnished with a black fringe, the uses of which are unknown. Birds appear to possess the power of enlarging or closing the pupil at will. In order that the iris should contract, it is necessary that the light should penetrate into the eye; if merely directed upon the iris, no motion is determined. The irritation of the iris with the point of a cataract needle does not occasion any sensible motion, as I have repeatedly satisfied myself by experiment. Messrs. Fowler and Rinhold found that the galvanic excitation directed upon the eye of man and animals caused contraction of the iris. Nysten likewise witnessed the same thing in the bodies of criminals recently executed. I have never repeated this ex- periment. In living man there is contraction from galvanism, but it differs much from the contraction that galvanism induces in the muscles. The shortening of the fibres is not sudden, but slow and gradual. Applied directly to the iris after death, galvanism does not excite the slightest contraction. 60 FUNCTIONS OF RELATION. If we divide the optic nerve in a living animal, it becomes di- lated and immovable; the same thing takes place in cats and dogs when we divide the fifth pair. In rabbits and Guinea-pigs, on the contrary, the pupil contracts from the section of the latter nerve. The division of the ciliary nerves causes also a cessation of the motions of the iris; Mr. Mayo asserts that the section of the third pair produces in birds, also, immobility of the pupil. Thus it appears that the motions of the iris are subject to much more complicated nervous influences than any other contractile organ. It is dependant on three nerves, the second, third, and fifth pairs. Nevertheless, in the arrangement of the fibres of this mem- brane, the effect of the will upon its contractions, and the abrupt manner in which they sometimes take place, seem to confound it with muscular motion. But it differs from it in this, that it can- not be excited by direct irritation; and as, after death has been suddenly induced, galvanism excites no motion in the iris, we must infer that the contractions of the pupil are analogous, but not identical with muscular motion.* The ciliary nerves in man come from two sources. The most numerous arise from the opthalmic ganglion, the others directly from the nasal nerve. It is probable that the first preside over the dilatation, and the second the contraction of the iris. But this is not, at present, fully proved.—(See Journal de Physiologiet t. iv.) Uses of the Motions of the Iris. The motions of the pupil influence vision in different ways. 1st. They modify the quantity of light that enters the eye. 2d. They influence the number and distinctness of the images formed at the bottom of the organ. 3d. They secure distinct vision at different distances. Let us examine successively each of these effects. It is easy to comprehend the advantages of the motions of the pupil with respect to the intensity of the light. It would injure ♦ the organ if it did not possess the power of closing itself, so as to receive only the quantity of light necessary to vision, but insuffi- cient to wound it. It is well known that this is accomplished when the light is very vivid. If we look at a bright light, as the sun, the vision is disordered, and the impression painful. The same thing happens when we pass from obscurity, where we have remained for some time, into a bright light; we are dazzled; the pupil becomes strongly contracted. If we are in darkness, the pupil dilates, so as to profit by the little light that may exist. Thus, after having remained for some time in a dark place, we * It has been observed, that in individuals weakened by venereal excesses, the pupil is very large, as well as in persons affected by intestinal worms, abdominal engorgement, hy- drocephalus, &c.; that an application of some of the narcotic plants to the conjunctiva, especially the belladonna, dilates the pupil; that in cerebral affections, the pupil is eithe» very much enlarged or contracted. The motions of the pupil »re generally an index of the sensibility of the retina. The consideration of the motions and the ?*nte of the pupil it>, then, very useful in medicine. SENSE OF VISION. 61 can discover objects, and soon distinguish them sufficiently for or- dinary purposes. When we wish to examine attentively a small object, the pupil diminishes. There is a double advantage in this. In the first lace, the contraction of the opening of the eye restricts the num- er of objects painted upon the retina, the attention so much the less distracted. Again, it is known that an image formed in a dark chamber is more distinct, and, of consequence, more visible, other things being equal, in proportion to the smallness of the opening through which the light enters. According to M. Mille, this result is in part caused by the diffraction which takes place at the edge of the pupil when the light passes through it* If an object be remote, it is desirable that we should see it dis- tinctly. The attention that we give in looking at it is accompa- nied with dilatation of the pupil; an effect, however, subordinate to the intensity of the light. We may infer from the preceding remarks, that the uses of the pupil are to place the eye in relation with the different degrees of intensity of the light and the distance of objects. It is in these motions, and not in the displacements or contractions of the crys- talline, that we must seek the reason of our seeing distinctly the same object at different distances. To render this evident, inject a drop of a solution of the extract of belladonna between the eye- lids ; at the end of a few hours the pupil will become dilated and immovable; this remarkable condition will sometimes remain for several days. It will be thus easy to judge of the influence of the motions of the iris on the habitual use of vision at different distances. These results are the easier to verify, as, in applying the belladonna to one eye only, we can compare it with the oth- er. The following results have been obtained by repeating these curious experiments: 1st. As soon as the pupil is dilated and immovable, objects ap- pear confused and enveloped in a mist. 2d. In using a common lens, we discover that the focus of the eye on experiment is twice as long as that of the eye which re- mains in its ordinary state. 3d. In proportion as the effect of the belladonna diminishes, these changes in the vision disappear.! If the pupil be dilated and immovable from any other cause than the belladonna, as e. g., certain diseases, the vision is modi- fied in a manner similar to that described above. Sir Everard Home cited the case of a young man who, in con- sequence of paralysis, lost the faculty of adapting his eyes to dif- ferent objects. It was impossible, for example, for him to read; all the characters were confused; on the contrary, he could dis- tinguish a pin at a distance of ten feet. * See, on this new question in optics, the learned memoir of this physician in the Journal de Physiologie, t. iv. t 1 have lately tried this experiment on a myopic young man. As soon as the pupil was dilated, the sight became longer, but he could not see distinctly except at a fixed distance; if closer or more distant, objects appeared confused and misty. 62 FUNCTIONS OF RELATION. Uses of the Choroid Coat. The principal use which this serves in vision is absorbing the light, immediately after it has passed through the retina, by means of the black matter with which it is impregnated. The effects found to be produced by a varicose state of the vessels of this* membrane must be considered as a confirmation of this opinion. In those individuals who are affected by this disease, the dilated vessels remove the black matter with which it is covered, and every time that the image of the object falls upon that point of the retina which corresponds to these vessels, the object appears to be spotted red. The state of vision in certain white animals, and in Albinoes, where the choroid coat and iris are not coloured black, strongly sustains this assertion. In them vision is extreme- ly imperfect during the day, so that they can scarcely see how to direct themselves. M. le Cat, and some others, have attributed to the choroid coat the faculty of perceiving light, but this opinion is completely des- titute of proof.* Uses of the Ciliary Processes. There have been no opinions advanced concerning the use of these parts but what are extremely vague and unsatisfactory; they are generally believed to be contractile. Some suppose that they are destined to move the iris, and others to move forward the crystalline humour. M. Jacobson asserts that their use is to dilate the openings which, according to him, the canal of Petit presents anteriorly, for the purpose of allowing the aqueous hu- mour to enter or be discharged from this canal, which would have the effect to displace the crystalline lens. Some persons imagine that the ciliary processes are secretory organs, for the produc- tion of the black pigment found on the posterior surface of the iris and on the choroid coat, or even of a part of the aqueous humour. Mr. Edwards, in a memoir on the Anatomy of the Eye, asserts that they contribute chiefly to the secretion of the aqueous hu- mour, an opinion before advanced by Dr. Young, Secretary to the Royal Society of London, in the Philosophical Transactions. M. Ribes has promulgated a similar opinion, with this difference: " he supposes that the ciliary processes maintain life and motion in the crystalline and vitreous humours." But there are many animals which have no ciliary processes, in which the humours exist. Haller supposed that they preserved the crystalline hu- mour in the most favourable situation. According to this anato- mist, they adhere to the capsule of this humour, both at their points and posterior side, by means of the black matter with which they are covered. * A great number of animals whose sight is excellent have the choroid of vivid or pear- ly colours.—See Mem. of M. Desmoulins, Journal de Physiologic, t. iv. SENSE OF VISION. 63 Action of the Retina. If we speak here singly of the action of the retina in vision, it is only to facilitate the study of this function. In reality, no dis- tinction exists between the action of this membrane and that of the optic nerve, much less of the sensorium. The action of the retina is a vital action, and its mechanism is completely unknown. The retina receives the impression of light when it exists within certain limits of intensity. A weak light makes no impression upon the retina, and a very strong light disables it from acting. When too brilliant a light strikes suddenly upon the retina, the ef- fect produced is called dazzling, and the retina remains for some moments afterward incapable of perceiving the presence of light. This effect is produced by looking steadily at the sun. When we have remained a long time in darkness, even a weak light dazzles us. If the light which falls upon the eye be extremely weak, and if we still endeavour to examine objects, the retina becomes very much fatigued, and we soon feel a sensation of pain in the orbit, and even in the head. A light, the intensity of wliich is not very great, but which acts during a certain time on a fixed point of the retina, causes insen- sibility in that point. If we look for some time at a white spot upon a black surface, and if we then suddenly turn our eyes to a white surfaec, we seem to see a black spot. It is because the retina has become insensible at the point which had been fatigued by looking at the white spot. On the other hand, when the reti- na has been for a long time without acting in some of its points, while the others have acted, the point which has remained in a state of repose becomes possessed of a much greater degree of sensibility, which causes objects to appear as if they were spotted. We may explain in this manner how it happens that, after having viewed a red spot for some time, white bodies appear spotted with green. In this case, the retina has become insensible to the ac- tion of the red ray, and it is well known that, when the red ray is taken from a beam of light, it produces the sensation of green. Similar phenomena occur when we look for some time on a red body, or those of any other colour, and then look suddenly upon white, or other coloured surfaces. We are enabled to distinguish with great accuracy the direc- tion of the light which is received upon the retina. We believe instinctively that the light passes in a right line, and that this line is a prolongation of that pursued by the ray, which has entered the cornea. Whenever the light, before arriving at the eye, has been modified in its course, the impression produced upon the re- tina is inaccurate. This is a principal source of those illusions which often take place in vision, and which are therefore called optical illusions. The retina may receive at the same time impressions over its whole extent, but then the sensations which result from them are very imperfect. It can only be strongly affected by the image of 64 ORGANS OF RELATION. one or two objects, although a much greater number are painted there.* The centre of this membrane appears to enjoy a more ex- quisite sensibility than its other parts. It is on this part that we receive the image when we wish to examine an object with at- tention. . . Does light act by simple contact with the retina, or is its pecu- liar effect produced by traversing this membrane ? The presence of the choroid, or, rather, of the black matter covering it, inclines us to the latter opinion. It has been said that the place that cor- responds to the centre of the optic nerve is insensible to the im- pression of light. I do not know of any fact which directly proves this assertion. All that has been said is exact as regards the phenomena of vision ; but, in affirming that they depend upon the retina, we are far from being rigorous, as many new facts, with which the science has become enriched, demonstrate. In the first place, physiolo- gists have agreed to regard the retina as the most sensitive part of the nervous system. The sensibility is so exquisite, they say, that the mere contact of so subtle an agent as light is sufficient to produce an impression. Now I have ascertained, from direct ex- periment, that the sensibility of the retina is very obtuse, if it ex- ists at all. I have, by means of a cataract needle, lacerated and pricked the retina without producing any obvious effect. The simple contact of a soft body with the conjunctiva causes a much more vivid sensation. Again, so far is the retina from being the prototype of the sensitive organs, that its sensibility may be ques- tioned.! * In birds of a high flight, whose sight is remarkably powerful, inasmuch as from their cloudy region they perceive and stoop upon their prey, the retina presents a great number of folds perpendicular to its surface; these folds project several lines into the hyaloid hu- mour. Perhaps they give to the bird the faculty of seeing both at a distance and near, as, by a slight motion of the whole" of the eye, the animal can make the image fall on points more or less distant from the crystalline; thus the focus may be made to vary to a consid- erable extent. Birds which fly but little do not have these folds. Birds have another or- gan not found in other animals: it is membranous, black as the choroid, which passes ob- liquely from the bottom of the eye, and traverses the central part of the vitreous humour, and is attached to the centre of the crystalline on its posterior face. The uses of this or- gan (peigne) are unknown. I have made some experiments on it. I have remarked that if it is divided, the cornea is no more drawn inward after death. Hence I have concluded that during life the (peigne) draws backward the crystalline and cornea, and may thus modify the curve of the latter, and vary the position of the crystalline. t I have assured myself frequently that pricking and tearing the retina do not cause pain to animals. I have verified in man, in the operation for cataract, by depression, that pressure with the point of the needle upon the retina produces no sensation. If I had ob- served this result only once or twice, I might still doubt; but I have observed and tried it so often, at the clinique of my hospital, that there does not remain the slightest uncertain- ty. Farther, the part occupied by the retina is the only part that is insensible; for if, in passing over the inner surface of the eye with the cataract needle, it is carried so far for- ward as to touch the iris, the patient manifests pain. Thus the iris is sensible, but the retina is not. The insensibility of the retina is most remarkable in a philosophical point of view. It shows strikingly the superiority of the experimental method over that which merely uses reasoning, and which supposes that just reasoning will enable us to attain all. What deduction could appear more logical than the great sensibility of the retina! The membrane which is sensible to the presence of light, may be supposed, would be most pain- fully affected by the contact of a palpable object, and that, if pricked or lacerated, the pain would be exquisite. AH this would appear true from reasoning; but a single experiment is sufficient to overthrow this apparently rigorous logic. How many similar reasonings will hereafter disappear before the progress of experimental physiology! Whatever may be the probability of a fact, let us never neglect to verify it by experiment. SENSE OF VISION. 65 But is the retina the nervous agent destined to receive the im- pression of light ? According to the ideas which have thus far prevailed, it is difficult to understand how such a question can be asked. Nevertheless, my experiments show that nothing can be more natural. I have divided the fifth pair of nerves in an ani- mal, and it has immediately lost the vision of that side. I have cut that of the opposite side, and the animal became immediately blind. The light of day, nor even a strong artificial light, con- centrated with a magnifying-glass, produced the slightest impres- sion. It is not easy to appreciate the trouble this at first caused me, after I had proved it by a great number of experiments. Can it be possible, I said, that the retina is not the principal organ of sensibility of the eye to light ? Is it possible that this belongs to the fifth pair of nerves ? To satisfy myself, I divided the optic nerve where it enters into the eye. If the fifth pair, or any other nerve, could perceive the light, the section I had made could not prevent it. But it was otherwise; the vision was completely abolished, as well as all sensibility to the strongest light, even that of the sun concentrated by a magnifying-glass. I subjected to this last test an animal in which the fifth pair of nerves was divi- ded. I easily found that if the eye, after having been obscured, was suddenly exposed to the direct rays of the sun, there was an impression, as the eyelid closed. All sensibility, then, is not lost in the retina by the section of the fifth pair; but it is only slight, and that membrane can only concur in vision under the influence of another nerve. We shall see hereafter that it is nearly the same in two other senses. Action of the Optic Nerve. There can be no doubt that the optic nerve transmits to me brain, instantaneously, the impressions made upon the retina by the light, but we are absolutely ignorant of the mode in which this is done. The optic nerve, when subjected to experiment, exhibits the same properties as the retina, with which it is continuous. It is insensible on pricking, cutting, or laceration, and its action in vis- ion is dependant upon the fifth pair. With respect to its crossing with that of the opposite side, no doubt can reasonably exist; the facts that I have reported I consider demonstrative.* This anatomical arrangement must undoubtedly have a great influence on the transmission of impressions received by the eyes, but it is a difficult point about which to form conjectures that have much probability. * M. Pouillet, in his Treatise on Physics, does not agree in this opinion. He believes that it may be true, perhaps, with regard to animals, but not in man, and that Woolaston has only spoken of the latter. To this I reply, that, with respect to the anatomical ar- rangements here referred to, man does not differ from the mammiferi. I will add, that, having had occasion to make my objections, in England, to that profound philosopher, whom the intellectual world has so many reasons to deplore, he did not appear to doubt that if the section of the decussation, over the sella turcica, produced blindness, it may be conclu- ded that the crossing is total, and not partial. I do not think that he insisted upon his con- jecture after the publication of my experiments. 66 FUNCTIONS OF RELATION. Action of both Eyes. Notwithstanding what has been said at different periods, and the efforts which have of late been made by M. Gall to prove that we only see with one eye at a time, it appears to me to be demonstrable, not only that both eyes concur at the same time in vision, but that it is absolutely necessary that they should act thus for the perfect performance of certain important acts of this func- tion. There are, however, circumstances in which it is conveni- ent to employ but one eye. For example, when we wish to jugde correctly of the direction of light, to take aim with a gun, or to ascertain if bodies are on a level, or in a right line. There is an- other situation where it is convenient to employ but one eye : it is when the two organs are unequal, either in refractive power or sensibility. It is for the same reason that we shut one eye when we look through a magnifying-glass. But, with the exception of these cases, it is much more effectu- al to use both eyes at the same time. The following experiment of my own appears to me to prove that both eyes see at the same time one object. Receive into a darkened chamber a beam of light upon a plain surface; then take glasses of sufficient thick- ness, each of which presents one of the prismatic colours, and place them in turn before the eyes. If the sight be good, and es- pecially if both eyes possess equal power, the image will appear of a dirty white, whatever may be the colour of the glass you employ. But if one of the eyes be much stronger than the other, you will see the image of the same colour as the glass. These results have been confirmed in the presence of M. Tillaye, junior, in the cab- inet of physic of the Faculty of Medicine. The same object, then, produces two impressions, while the brain perceives but one ; but for this purpose it is necessary that the motions of the eye should be in harmony. If, in consequence of disease, the regular mo- tions of the eyes be interrupted, we then receive two impressions instead of one ; and this it is which constitutes strabismus. We may likewise voluntarily receive two impressions instead of one; we have only to interrupt the harmony in the motion of the eyes to produce this effect. The harmonious action of the eyes is said to exist in all the red- blooded animals except the chameleon, in which these organs have a separate and independent action; a peculiarity which gives a re- markable expression to the physiognomy of this animal. On estimating the Distance of Objects. Vision is essentially produced by the contact of light with the retina, though we are constantly in the habit of referring the eause of the sensation to the bodies from which the light passes, notwithstanding they are at a great distance. It is plain that this must be the effect of an intellectual process. Our judgment of the distances of bodies is very materially af- fected by their remoteness. We judge with accuracy when they SENSE OF VISION. 67 are near us; but it is not so when they are very remotely situa- ted ; then our judgment is often erroneous ; but, when objects are at a very great distance, we are constantly in error. The united action of both eyes is absolutely necessary to judge exactly of the distances of objects, as may be proved by the fol- lowing experiment. From a thread suspend a ring, then fix to a rod a hook, which will readily enter the ring. Place yourself at a convenient distance, and endeavour to introduce the hook. If you use both eyes, you will readily succeed at each attempt; but if you shut one eye, and then endeavour to hook the ring, you will fail. The hook will either go beyond or fall short of the ring, and it will only be by accident, and after many fruitless attempts, that the hook will be introduced. Persons whose eyes possess une- qual power, will not succeed in this experiment even when they use both eyes. When a person loses one eye by accident, it often happens that they will not be able to judge accurately of distances for more than a year. I once saw a remarkable case of this kind, where the person, for several months afterward, had to make several attempts before he could seize those objects which were placed even very near to him. Generally speaking, persons who have but one eye judge very inaccurately of distances. The size of objects, the intensity of the light which passes from them, the presence of intermediate objects, &c, influence very much the ac- curacy of our judgment with respect to the distances of objects. Our judgment is much more exact when the objects are placed on the same plane with ourselves. Thus, when we look from a high tower upon objects situated below, they appear to us much small- er than when they are viewed at the same distance on the same plane with ourselves. The same observation applies to objects placed far above us; and from this we see the necessity of giving a considerable volume to those objects which we place in eleva- ted situations for the purpose of being seen at a distance. The smaller the object, the more necessary it is that it should be placed near to the eye to be seen distinctly. That which may be called the point of distinct vision, therefore, varies very much. We see a horse distinctly at thirty feet distance, but we do not see a bird distinctly at the same distance. If we wish to examine a hair or feather of these animals, they must be brought very near to the eye. At the same time, the same objects may be seen with equal distinctness at different distances. For example, it is indif- ferent to many persons whether they place a book, when reading, at the distance of one or two feet from the eye. The intensity of light thrown upon an object influences very materially the dis- tance at which the object may be seen distinctly. On estimating the Size of Bodies. The correctness of our judgment respecting the size of bodies depends more upon sagacity and habit than upon the particular action of the apparatus of vision. We form our judgment of the 68 FUNCTIONS OF RELATION. dimensions of bodies from the size of the image formed at the bot- tom of the eye. the intensity of the light which passes from the object, the distance at which we suppose it to be placed, and espe- cially from our habit of seeing similar objects. This is the reason why our judgment of the size of bodies that we see for the first time is so faulty, when we do not know the distance. A mount- ain, seen at a distance for the first time, appears to us generally much smaller than it really is, because we think it to be much nearer than it actually is. Beyond a very inconsiderable dis- tance, we fall into an illusion which the judgment cannot over- come. That objects at a distance appear infinitely smaller than they actually are, is sufficiently evident from the appearance of the celestial bodies. On estimating the Motion of Bodies. We judge of the motion of bodies by that of the image upon the retina, and by the variations in the size of this image; or, what amounts to the same thing, by the change in the direction of the light which arrives at the eye. In order that we may follow the motion of a body, it is neces- sary that the image should not be displaced too rapidly, for then we cannot perceive it. This is the case with projectiles thrown by firearms, when they pass very near us ; but when they move at a distance, if they be of considerable size, as they are exposed for a much longer time to the eye, the field of vision being great- er, we can then distinguish them. To judge correctly of the mo- tion of bodies, it is necessary that we should ourselves be at rest. We distinguish with difficulty the motion of the bodies which are at a distance, especially if they leave or approach us. In- deed, in this case we can only form our judgment of the motion of the body by the variation in the size of its image. Now this variation being infinitely small, when the body is at a distance it is extremely difficult, and often absolutely impossible, to appreci- ate it. Generally, we distinguish with great difficulty, and often we cannot perceive at all, the motion of bodies which are displaced very slowly. This may arise from the real slowness of the mo- tion, as in the case of the hand of a watch, or it may arise from the slowness with which the image moves over the retina, as that of the stars and very distant objects. Optical Illusions. From what has been said of the manner that we judge of the distance, size, and motion of objects, it is easy to perceive that we are exposed to numerous errors. These errors are distinguished in science by the name of optical illusions. We judge, for the most part, with sufficient accuracy of those objects which are placed near to us, but are frequently deceived with respect to those which are at a distance. The illusions into which we fall with respect to neighbouring objects arise either from the reflec- SENSE OF VISION. 69 tion or refraction which the light undergoes before arriving at the eye, and to that law which we instinctively establish in our own mind, namely,, that the light passes from the object to the eye in a straight line. It is to this cause that we must refer the illusions occasioned by mirrors. We see the object behind the mirror in a prolongation of the line that the ray describes in directly ap- proaching the eye. To this cause must be referred the apparent increase or diminution of volume of bodies seen through glass. If the rays are made to converge, the body will appear to us lar- ger ; if to diverge, it will appear smaller. The use of these glass- es produces another illusion. The objects appear surrounded by the different colours of the solar spectrum, because the surfaces of glass, not being parallel, decompose the rays of light in the manner of a prism. Distant objects are constantly producing illusions, which we cannot prevent, because they necessarily result from certain laws that govern the animal economy. An object appears so much the nearer to us as its image occupies a more considerable space upon the retina, or as the light passing from it is more intense. Of two objects, of different volume, equally brilliant, and placed at equal distances, the largest will appear the nearest, unless there be some accidental circumstance that enables us to judge more correctly. If two objects of equal volume be placed at equal dis- tances from the eye, but are unequally bright, the most brilliant will appear the nearest. It would be the same if the objects were at unequal distances. This any person may convince themselves of by observing a row of reflectors ; if the light of one be more intense than the rest, it will appear to be the first of the row, while that which is really first will appear last, if it be less bright. An object which is so placed »as not to have anything between our eye and it, will appear nearer than when this is not the case; the reason of which is, that intermediate objects enable us to com- pare distances, and thus to form a more exact judgment. When our eye is attracted by a bright object, while those sur- rounding it are enveloped in darkness, it appears much nearer than it is in reality. Every one must have noticed this effect of a light at night. Objects appear small according to their distan- ces ; thus the trees in a long avenue appear to us to grow smaller and approach each other when they are at a considerable dis- tance. It is by attending to these various sources of illusions, and the laws of the animal economy in which they are founded, that artists are enabled to produce them at pleasure. The paint- er, for example, in many cases, does nothing more than transfer to his canvass those optical illusions into which we are constantly falling. The construction of optical instruments is also founded on these principles. Some augment the intensity of the light coming from objects; others, by rendering it divergent or con- vergent, increase or diminish the apparent volume of objects, &c., &c. There are some optical illusions which we are able to remove 70 FUNCTIONS OF RELATION. by experience and the exercise of the other senses. The follow- ing extremely curious history of a blind man restored to sight, related by the celebrated Cheselden, is strikingly illustrative of this: " When he first saw, he was so far from making any judgment of distances, that he thought all objects whatever touched his eyes, as he expressed it, as what he felt did his skin, and thought no objects so agreeable as those which were smooth and regular, though he could form no judgment of their shape, or guess what it was, in any object, that was pleasing to him : he knew not the shape of anything, nor any one thing from another, however dif- ferent in shape or magnitude; but, upon being told what things were, whose forms he before knew by feeling, he would carefully observe, that he might know them again ; but, having too many objects to learn at once, he forgot many of them ; and, as he said, at first he learned to know, and then forgot, a thousand things in a day. One particular only, though it may appear trifling, I will relate: having often forgotten which was the cat and which the dog, he was ashamed to ask ; but catching the cat, which he knew by feeling, he was observed to look at her steadfastly, and then setting her down, said, ' So, puss, I shall know you another time.' He was very much surprised that those things which he had liked best did not appear most agreeable to his eyes, expecting those persons would appear most beautiful whom he loved most, and such things to be most agreeable to his sight that were so to his taste. We thought he soon knew what pictures represented when showed to him, but we found afterward that we were mis- taken ; for about two months after he was couched, he discover- ed that they represented solid bodies, when, to that time, he con- sidered them as party-coloured planes, or surfaces diversified with variety of paint; but even then he was no less surprised, expecting the pictures would feel like the things they represented, and was amazed when he found those parts which, by their light and shad- ow, appeared now round and uneven, felt only flat like the rest, and asked which was the lying sense, feeling or seeing. Being shown his father's picture, in a locket in his mother's watch, and told what it was, he acknowledged a likeness, but was vastly sur- prised, asking how it could be that a large face could be express- ed in so little room; saying, it should have seemed as impossible to him as to put a bushel of anything into a pint. At first he could bear but very little light, and the things he saw he thought extremely large; but, upon seeing things larger, those first seen he conceived less, never being able to imagine any lines beyond the bounds he saw ; the room he was in, he said, he knew to be but part of the house, yet he could not conceive that the whole house could look any bigger. " When couched of his other eye, he says that objects at first appeared large to this eye, but not so large as they at first ap- peared to the other: and looking upon the same object with both SENSE OF VISION. 71 eyes, he thought it looked about twice as large as with the first couched eye only, but not double."* This case does not stand alone, but others very similar to it have been witnessed by other surgeons. A case of this kind occurred in 1819 at the Hotel Dieu at Paris. The patient Was a little girl six years of age, who was sent from the environs of Beaune to be operated on for a congenital cataract of the right eye, the left being in a state of atrophy. The vision was entirely lost; the other senses had acquired a devel- opment that supplied the defect. The manner that this child used its senses was remarkable. If called, she accurately distinguished by her ear the point from which the sound came ; she went imme- diately to the place, holding her hands before her as feelers, and lifting her feet high, as if ascending steps, and carefully putting them down, as if to avoid a precipice. If she placed her hand in contact with a body, she generally recognised by the sense of touch; if doubtful, she subjected it to the sense of smell; if she thought it suitable for eating, she applied it to her tongue. This mode of examination she constantly pursued when any one at- tempted to deceive her ; then the vigilance of her senses became doubled, and it was difficult to evade them. But, notwithstand- ing the extreme susceptibility of her organs of sense, they were only applicable to a very limited range of objects connected with animal life and instinct; the little patient seemed incapable of fol- lowing a connected chain of reasoning. She was operated upon successfully. Twelve days after the operation, she could walk about without a guide, and could see sufficiently well not to injure herself. But she had no idea of distances, and reached out her hand for anything that was offered, however distant. It was the same if any one pointed out a par- ticular object; she would reach beyond it, and would seek it by several attempts before attaining it. If a lighted candle was placed before her, she appeared to have great pleasure in looking at it, and following it with her eyes when moved about. If any one placed their hand between her eye and the light, she would immediately endeavour to remove it. In numerous experiments, it was evident that she perceived all the objects presented, but could not distinguish either their colour or form. Various un- successful attempts were made to teach her these qualities and make her repeat their names. But at the end of two months after the operation, the power of vision remained nearly the same; no improvement had taken place. It was quite evident that the fac- ulty of vision existed; it only remained to ascertain what prevent- ed the exercise of it. It was easy to perceive that the child did not look; but it is necessary to look in order to see. It was necessary, then, to teach her to look ; that is to say, to direct her eyes and fix her attention upon objects. This was a tedious and difficult occupation for her, *• I have preferred an abstract of this case in the language of the author to a translation. — Trans. 72 FUNCTIONS OF RELATION. and she made but little progress. It was soon observed that the; habit she had acquired of supplying the place of vision by the other senses prevented her making use of it. To make her aware of its value, it was necessary to deprive her of hearing, smelling, and the use of her hands to some extent; especially of the latter, of which she made great use. With this object, her hands were secured behind her back; thus she was compelled to look, to calculate distances, and to guide herself by her eye. Soon she acquired the habit of walking with her head erect, and consider- able confidence. These improvements, however, could not con- ceal the effect of the habit, contracted from infancy, of depending upon the sense of hearing, and which obstructed the attention from that of seeing, and prevented her obtaining the full advantage of it. The use of this sense was therefore suspended by closing the ears, while the hands were kept secured to the back. The deprivation of these two senses seemed to astonish her very much at first; but she soon began to walk about again, and could do so without injuring herself. Wishing to ascertain if any other sense than that of vision had taken the place of touch and hearing, a black bag was placed over her head, releasing her hand and ears. On doing this, she walked with hesitation, and groping her way. It was thus evident that she directed herself by her eyes. Her habits now changed, her relations and wants became multiplied. Before the operation, she remained in bed or in a chair; her movements were without aim, and similar to those of certain ani- mals when enclosed in a narrow cage; but after the operation she insisted on leaving the bed and walking about Soon she walked about alone, preceded and followed the visiters, mingled with a crowd and disengaged herself from it without using her hands, which were still kept secured behind her back. She knew the other patients, found easily her own bed, sought their society, rendered them small services, appeared to comprehend them, and obeyed their directions, but made no attempt to speak herself. Finally, after two months and a half of careful and persevering attention, she had made so much progress in the education of the sense of vision that she could go alone, without the assistance of her hands, to every part of the hospital, return to her bed, attend to all her wants, and enjoy games before unknown and impracticable for her. This acquisition of a sense before unknown already had exerted an influence over her mind. She was still incapable of maintaining a conversation, but she was susceptible of attention. She was frequently overheard repeating questions that had been addressed to her, or repeating words she had heard. These so- liloquies appeared the preludes to conversation, but which she still refused to attempt. It is probable that, by persevering in these at- tentions, her intelligence might have become developed, but the rules of the hospital not permitting her remaining longer, she was sent back to her friends. We may draw the following inferences from these facts, viz., that the exact judgment which we become capable of forming of SENSE OF VISION. 73 the distances, magnitudes, and forms of bodies is the result of ex- perience, or, what amounts to the same thing, of the education of the sense of vision. This will be confirmed by considering vision at different periods of life. Vision at different Periods of Life. The eyes are early formed in the foetus* In the embryo, they appear like two black spots; at seven months they be- come capable of modifying the light, so as to form an image upon the retina, as we know by experiment; until that period they cannot do this, because the pupil is closed by the membrana pu- pillaris* At seven months this membrane disappears. The common mode of expressing this is saying that it is ruptured; it is probably absorbed. At this period the foetus likewise becomes capable of living independently of the mother; it sometimes hap- pens, however, that no trace of this membrane is found in the eyes of the foetus at six, or even five months. There are some points in which the eyes of the foetus and those of adults differ; they are not, however, very remarkable. In the first, the sclerotic coat is thinner, and even slightly transparent; the choroid is reddish externally, and the black pigment less thick internally; the retina is proportionally more developed, and the aqueous homour is more abundant, which causes the cornea to project; finally, the crystalline humour is much less dense than in the adult. Before birth, the eyelids are closed tightly together, as if they were glued; in some animals they are even united by the conjunctiva of the eyelids, which passes from the one to the other, and is not ruptured until after the birth. As we advance in life, the quantity of the humours of the eye insensibly diminish until the adult age. After this, they diminish in a manner much more perceptible ; this becomes very palpable in advanced age. The crystalline humour, especially, not only becomes more dense, but it begins to lose its transparency, and to assume a yellow colour, which at last becomes quite deep. At the same time that the crystalline becomes yellow, it becomes much more dense, and contracts a slight opacity that may in- crease with age, until it becomes completely opaque. Another modification of the eye worthy of remark is this. The choroid is of a brownish black in infants ; it is a little less deep at twenty; at thirty it becomes grayish, and it continues to in- crease with age, so that at eighty years the choroid is nearly colourless. We learn from experiment that the eye of the newborn infant, then, is very well adapted to act upon the light, and to form ima- * According to M. Edwards, the membrana pupillaris is formed by a prolongation of the membrane of the aqueous humour, and by the external lamina of the choroid coat. Ac- cording to this anatomist, there is no aqueous humour in the anterior chamber of the eye before the rupture of this membrane, but this humour is accumulated in the posterior Chamber, which proves, 1st, that the membrane of the aqueous humour is not the secre- tory organ of this fluid ; 2d, that this organ exists in the posterior chamber; 3d, that before the seventh month, the membrane of the aqueous humour presents all the characters of a Berous membrane, particularly that of forming a sac without an opening. 74 FUNCTIONS OF RELATION. ges upon the retina. During the first month of its life, however, the infant gives no evidence of its being sensible to the light. Its eyes move slowly, and in a doubtful manner. It is not until the seventh week that it exhibits strong proofs of its sensibility in this respect. Even then it is only attracted by a very brilliant light. It seems pleased to look upon the sun at first, but soon becomes sensible merely to the light of day. In the mean time, however, it seems indifferent to other objects ; the first which it notices are generally of a red, or some other brilliant colour. At the end of some days, its attention is arrested by bodies of different colours, but it is a long time before it becomes capable of forming any idea of the distance or size of bodies. It extends its hands to seize even the most remote objects ; and, as the first of its wants is food, it endeavours to carry to its mouth everything it gets hold of, whatever may be its nature or dimensions. It appears, therefore, that vision is extremely imperfect during this early period of life; but from exercise, and especially from experience, resulting from continual mistakes, the sight becomes perfected by a sort of edu- cation. It has been asserted that children see objects double and re- versed ; this assertion, however, is entirely unsupported by any proof. It has been said, also, but without any more reason, that the refracting parts of the eye being more abundant, they see ob- jects much smaller than they actually are. Vision soon acquires all the perfection of which it is susceptible, and in general it un- dergoes no modification until the approach of old age. It is then that the changes which we have pointed out in the humours tend to render it more distinct; but what principally contributes to this effect is the diminished sensibility of the retina. Three causes affect vision in old age, viz.: 1st. The diminution of the quantity of the humours of the eye, a circumstance that di- minishes the refractive powers of the organ, and prevents the in- dividual from distinguishing accurately near objects. He is obli- ged, in order to examine them, either to hold them at a distance, so that the light which penetrates into the eye is less divergent, or to employ convex glasses, which diminish the divergence of the rays. 2d. Commencing opacity of the crystalline humour, which weakens the vision, and, increasing, tends to cause blind- ness, by producing the disease generally known by the name of cataract. 3d. The diminished sensibility of the retina, or, if you choose, of the brain, which renders obtuse the perception of im- pressions produced upon the eye, and often terminates in complete and incurable blindness.* * Most physiologists consider the diminution of the black tint of the choroid, and the disappearance of the coloured coat from the iris, as circumstances unfavourable to seeing in old age ; but, from the researches of M. Desmoulin, it appears that this idea is not well founded. Indeed in a great number of animals the choroid is totally or partially of a bright or pearl colour, but they are, nevertheless, remarkable for their vision. The pupils in these animals are in the form of a chink or cleft when they are contracted. Such is the case with cats, horses, foxes, &c. If in these animals the brightness and reflection of the choroid concur for the perfection of vision, it would seem probable that the disappear- ance of the colour from the choroid in an old man would benefit instead of injuring his vision J ° SENSE OF VISION. 75 Imperfection of Vision. [Myopia, or shortsightedness, arises generally from a congenital malformation of the eye, in consequence of which the refractive power is too great relatively to the distance between the crystal- line and the retina. Hence the rays coming from objects placed at a certain distance from the eye form their focus too near to the crystalline, and, consequently, trace upon the retina confused im- ages. This imperfection arises sometimes from too great convexi- ty of the cornea; but it may depend also upon the state of the in- terior of the eye, as the form of the crystalline or the density of the humours. Whatever may be the cause, it generally dimin- ishes with age, because the eye, becoming less distended by the fluids, loses a portion of its anterior convexity. Myopic persons remedy this indistinctness of vision by placing objects very near to the eye, so that the rays which pass from them, being very divergent, form a focus upon the retina. This approximation of objects being always inconvenient, and often impracticable, spectacles, the glasses of which are either plano- concave or bi-concave, are used to obviate the defect. They are more or less curved, the degrees being indicated by numbers. When these glasses are placed before and near the eye, they re- ceive the rays coming from objects, and *y their refraction in- crease the divergence, so as to compensate exactly for the in- creased refraction of the eye. Presbyopia, or farsightedness, is seldom congenital, but gen- erally comes on in old age. It is consequent upon such an ar- rangement of the organ that it only receives distinct images of objects that are very remote; and which send to it rays nearly parallel, while near objects, the rays from which are divergent, form their focus beyond the retina. It is obvious that this affec- tion is the opposite of myopia, and arises from a defective refract- ing power in the eye, which is generally attributed to a diminu- tion of the humours, in consequence of which there is diminished convexity of the cornea. It is remedied by glasses more or less convex, which, by their refraction, diminish the divergence of the rays coming from near objects, so as to form a focus upon the retina. Cataract is sometimes a congenital disease, but it more fre- quently arises at an advanced period of life. It consists for the most part in an opacity of the crystalline, and is developed more or less rapidly. Various ingenious methods have been resorted to by surgeons to remove this obstacle to vision, by extracting or depressing it, when it is often rapidly absorbed. When patients have undergone this operation, and the inflammation that often results from it is completely dissipated, the power of perceiving the light again returns ; but they can only distinguish imperfect- ly, because the eye has lost one of the chief means of making the rays converge upon the retina. Such persons are obliged to use 76 FUNCTIONS OF RELATION. spectacles which are strongly convex; but even then the vision is rarely very distinct. In selecting glasses to assist in correcting defective vision, it is of importance that the compensation be not excessive, as its ten- dency always is to increase the defect. It is better that the cur- vature of the lens be rather under than too high, especially in myopia, as advancing years tend to correct the defect. The glass should neither magnify nor diminish the object, but only render it more distinct. Of the nine pairs of nerves that arise from the base of the brain, four are appropriated to the eye; and all, with the exception of the second pair, or optic nerves, are simple motor nerves. Be- sides these, there are numerous branches of the fifth, and portio dura of the seventh, distributed to this organ. The eyes are in- timately connected with the encephalon, not only by the numer- ous nervous relations of which we have now spoken, and by their proximity, but they also receive branches directly from the ante- rior cerebral artery. From the exceeding delicacy and complicated arrangements and relations of these organs, we might anticipate their peculiar liability to disease. Besides the numerous casualties incident to their structure and functions, their close connexion with the brain necessarily implicated them in almost every morbid condition, while their marked influence on the expression of the countenance directs the attention of the physician to them as one of his surest guides in judging of the pathological conditions of the body.* It is manifest that they must directly sympathize in any change in the functions or organic actions of the encephalon. Whatever excites or depresses it will necessarily increase or diminish the innervation of these organs and their appendages, while any change in the circulation of the brain must necessarily extend to, and have a corresponding effect upon, the eyes. Thus, in health, we may read the state of the mind, and almost every passing emotion, in the expression of the eyes. In disease, their dulness and insensibility, or their restlessness and morbid excitement, af- ford indications of the state of the encephalon, which cannot be readily misunderstood. Their contracted pupils, redness, fierce- ness, and extreme sensibility to light, so common symptoms in the earlier stages of the severer forms of the idiopathic fevers and some other diseases, mark with certainty the tendency to, or ac- tual existence of, inflammation in the cerebral textures; while their languid expression, expanded iris, musci volitantes, and loss of consentaneous motion, show with equal certainty loss of power in the great centre of the nervous system. Again, intense and long-continued use of the eyes not only induces redness in these organs themselves, but, from the cephalalgia and vertigo which are so apt to ensue, no doubt, also, hyperaemia of the encephalon. * Hippocrates remarks, " Ita valet corpus sicuti valent occuli: cum illi bene videntur valere—corpus valet."—Epidemics, lib. iii. SENSE OF HEARING. 77 Amaurosis generally affects the whole of the retina; occasion- ally, however, it confines itself to one or more parts, and thus produces some remarkable anomalies. Thus blank spots appear in the field of vision: when the paralysis is confined to certain points of the retina, or if considerable portions, say one half, of the membrane be diseased, the individual sees only parts of objects. Amaurosis may arise from the morbid condition of the retina, the trunk of the optic nerve, or a portion of the brain. It not unfre- quently arises in one eye, while the other remains perfect; some- times occurring without pain, or even the consciousness of the individual, a knowledge of its existence being revealed to him, perhaps, in accidentally shutting the well eye to examine an ob- ject with the other. Partial and temporary paralysis, causing indistinctness of vision, musci volitantes, &c, not unfrequently arises from sympathy with the disordered state of the stomach.] CHAPTER IV. OF HEARING. Hearing is the function by which we are made acquainted with the vibratory motions of bodies. Sound is to hearing what light is to vision. Sound is the result of an impression produced upon the ear by the vibratory motion impressed on the particles of bodies, by percussion or any other cause. This word describes also the vibratory motion itself. When the particles of a body have been thus put in motion, they communicate it to the elastic bodies which surround them ; these act again in the same man- ner, and thus the vibratory motion is propagated, oftentimes to a considerable distance. Elastic bodies alone, generally speaking, are capable of producing and propagating sound. For the most part, solid bodies produce it, while the air is often the vehicle which transmits it to our ear. We may consider it according to its intensity, note, and tone. The intensity of sound depends on the extent of the vibrations. The note depends on the number of vibrations in a given time, and is divided into sharp and grave. A grave note arises from few vibrations; in a sharp note tthey are very numerous. The most grave note that the ear can perceive is formed by thirty vibrations in a second; the most sharp, by twelve thousand. But M. Savart has proved, by a series of experiments and ingenious instruments, that the ear can appreciate sounds when there are 48,000 vibrations in a second.* Between these two extremes are included all appreciable sounds, that is, all sounds of which the * See Annal. de Physiologie et Chimie, Octobre, 1830. 78 FUNCTIONS OF RELATION. ear instinctively perceives the vibrations. Noise differs from an ap- preciable sound in this, that the ear cannot distinguish the number of vibrations of which it is formed. An appreciable sound, which is composed of double the number of vibrations of another sound, is called its octave. Between these two are seven intermediate sounds, called the diatonic scale, or gammut; they are distinguished in France by the names ut, re, mi, fas, sol, la, si. When we put in motion a sonorous body, by percussion, we hear at first one distinct sound, more or less intense, or more or less sharp, as the case may be. This is the fundamental sound. With a little attention, one perceives that it produces at the same time other sounds; these are called harmonics ; this will be readily observed by striking the chord of an instrument. The note depends on the nature of the sonorous body, and also upon the greater or less number of harmonics produced at the same time as the principal sound. Sound is propagated by all elastic bodies. The velocity with which it moves varies according to the body that serves to prop- agate it; it moves through air at the rate of a thousand and forty- two feet in a second; its transmission is still more rapid through water, stone, wood, &c* It generally loses its force in passing, in a proportion which is directly as the squares of the distances. This, however, is only in passing through air; sometimes its in- tensity is increased in passing; this is the case when it traverses very elastic bodies, as certain metals, wood, condensed air, &c. Sharp, grave, intense, and weak sounds are propagated with equal rapidity, and without being confounded. It has been generally supposed that sound is propagated in a right line, forming cones analogous to those of light, with this essential difference, that cones of sound have only an oscillatory motion, while those of light are progressive. When a chord is in unison with another chord, that is, when it produces the same sound if put in vibration in the same man- ner, it presents a remarkable property: it vibrates and produces its peculiar sound, if this sound is produced in its neighbourhood. This property of the unison of chords has been long understood, but it was not so well known that all bodies are susceptible of vibra- tions, and of presenting phenomena analogous to those of chords. M. Savart has shown, by a series of ingenious experiments, that all elastic membranes, dry or humid, vibrate and transmit sound if the sonorous vibrations are heard near these membranes, without their being in unison with the bodies which produced the vibrations. M. Savart has also proved that the different degrees of tension of membranes, their thickness, homogeneity, humidity, &c, have a remarkable influence on the facility with which they vibrate by communication; but that, whatever may be their state, they vibrate always in unison with the sound produced. This law * Vide Memoirs d'Arcueil, vol. ii. SENSE OF HEARING. 79 is also common to all bodies. These experiments are the more interesting, as the greater part of the organs of hearing is com- posed of elastic membranes and laminae, as we shall now see. When sound meets with a body that opposes it, it is reflected in the same manner as light, that is, the angle of incidence is equal to the angle of reflection. The form of the body which reflects sound has a similar influence. The slowness with which sound is propagated produces certain phenomena, the reason of which may be easily explained; such, for example, as echo, the mysteri- ous chamber, whispering gallery, &c. Apparatus of Hearing. This organ is very complicated, but we shall not enter into minute anatomical details, for at present we know but little of the uses of the different parts that constitute this apparatus. As in the apparatus of vision, so in that of hearing, we find a collection of organs, which concur in their physical properties, and behind them a nerve destined to receive and transmit im- pressions. The apparatus of hearing is composed of the external, middle, and internal ear, and auditory nerve. [The following diagram will give an idea of these different parts: C is the external cartilage. M the meatus auditorius externus. B is the middle ear. It consists of the membrana tympani D, by which the external is separated from the middle ear; the chain of small bones, B, by which the tympanum is connected with the fenestra ovalis. T is a hollow space, called the cavity of the tympanum, of an irregular shape, and scooped out of the petrous portion of the temporal bone. E is the eustachian tube, or meatus auditorius internus, which begins in the cavity of the tympanum, of a small size, and enlarging as it extends, opens at the back part of the nostrils. The internal ear consists of the parts indicated by V S K, the labyrinth: the first, V, is called the vestibule; S, the semicircular canals; K, the cochlea; N, the auditory nerve.] 80 FUNCTIONS OF RELATION. External Ear..—W e shall comprehend under this denomination the external cartilage, and the meatus auditorius externus. External Cartilage.—The size of the external cartilage is dif- ferent in different individuals. The external face, which in a well- formed ear projects a little forward, presents on its anterior sur- face five eminences, called the helix, ante-helix, tragus, ante- tragus, and the lobule. There are likewise three cavities, viz., that of the helix, the scapha, and the concha. This cartilage is very elastic; the skin which covers it is thin and dry, and is at- tached to the cartilage by a strong cellular tissue, which contains but little adipose substance, but the lobule contains a large quan- tity. Beneath the skin is seen a large number of sebaceous folli- cles, which furnish a white and shining matter, which gives to the skin its polish, and, perhaps, a part of its flexibility. There is likewise seen on the different prominences a few muscular fibres* This part receives many nerves and bloodvessels, is very sensible, and easily becomes red. It is attached to the head by ligaments of cellular tissue, and muscles called, according to their positions, anterior, superior, and posterior. These muscles are very much developed in many animals, but in man they can only be con- sidered as vestiges* Meatus auditorius externus.—This part extends from the con- cha to the membrana tympani, its length varying according to the age; in the adult it is from ton to twelve lines. It is narrow- est at the middle part, and is slightly curved upward and for- ward. At its external orifice it is furnished with hairs, like the entrance to the other cavities. It is composed of bone, and a fibro- cartilage, which is confounded with the external cartilage, and a fibrous part which completes it above ; the skin with which it is covered is thin, and is expanded over the external surface of the membrana tympani. Beneath this skin there are a great number of sebaceous glands, which secrete the cerumen, or wax—a yellow, bitter, and unctuous substance, the uses of which will hereafter be pointed out. Middle Ear.—The middle comprehends the cavity of the tym- panum, the small bones contained in it, the mastoid cells, and the eustachian tube, &c. The tympanum is the cavity which separates the external from the internal ear. Its form is that of a portion of a cylinder, some- what irregular. Its internal wall presents above an oval hole, called the foramen ovale, which communicates with the vestibule, and is closed by a membrane ; immediately below is a small pro- jection, and beneath this a cleft, in which is lodged a nervous fila- ment ; still lower, there is a round opening called the foramen ro- tundum, which corresponds to the external scala of the cochlea, and is also covered by a membrane. The external opening of * The name vestiges is given by the French anatomists to those parts of animals which are without any perceptible use, but which seem only intended to indicate the uniform plan that nature has pursued in the construction of animals. SENSE OF HEARING. 81 the tympanum is covered by a membrane called the membrana tympani. This membrane passes obliquely downward and in- ward ; it is tense, very thin, and transparent; it is covered exter- nally by an expansion of the skin, and internally by a mucous membrane, which lines the tympanum ; it is also covered on this side by a nerve, called the cord of the tympanum; its centre gives attachment to the handle of the malleus ; its circumference is attached to the osseous extremity of the meatus auditorius ex- ternus, and it adheres firmly at every point, affording no opening by which the external and middle parts of the ear can communi- cate with each other. Its texture is dry, fragile, and has nothing analogous to it in the animal economy; there cannot be distin- guished about it either fibres, or bloodvessels, or nerves. The circumference of the tympanum presents anteriorly, 1st. The eustachian tube, by which the tympanum communicates with the superior part of the pharynx. 2d. The opening by which the tendon of the internal muscle of the malleus enters. Posteriorly is seen, 1st. The opening into the mastoid cells, which are ir- regular cavities always filled with air, opening into the thickest part of the mastoid process. 2d. The pyramid, a small hollow projection, which gives attachment to the muscle of the stapes. 3d. The opening by which the cord of the tympanum enters into this cavity. Below there is a small cleft called "gleniodale" by which the tendon of the anterior muscle of the malleus enters, and the cord of the tympanum passes out to anastomose with the lingual nerves of the fifth pair. Above there is nothing but small openings through which bloodvessels pass. The tympanum, and all the openings with which it abounds, are covered by a very delicate mucous membrane. This cavity is always filled with air, and contains four small bones, viz., the malleus, the incus, the os orbiculare, and the stapes, which are so connected together as to form a chain, extending from the membrana tympani to the foramen ovale, where the base of the stapes is fixed. [In the following figures these four bones are distinctly deline- ated: (Fig. 12.) These minute bones are sometimes called the tympanic ossicula; they are here magnified, and represented separately. The first, M, represents the malleus, or hammer; the second, I, is the incus, or anvil; the third is the smallest bone in the body, being about the size of a millet seed, called the os orbiculare; and the last, S, the stapes, or stirrup. In the preceding figure, these minute bones are placed in situ naturale. The malleus, with its long handle, is 82 FUNCTIONS OF RELATION. seen at B, attached to the membrana tympani, and the stapes with its base attached to the fenestra ovalis. These minute bones are regularly articulated, with all the arrangements of other joints, and are moved by small muscles provided for the purpose. Their office is obviously to transmit the vibrations of the tympa- num to the fenestra ovalis, probably at the same time increasing their force.] There are small muscles destined to move this chain, and to stretch and relax the membranes to which it is at- tached. Thus the internal muscle of the malleus draws it anteri- orly, moves the whole chain of small bones, and stretches the membranes. The anterior muscle produces an opposite effect. We may suppose, also, that the small muscle lodged in the pyra- mid, and which is attached to the neck of the stapes, may produce a slight tension upon the chain, drawing it towards itself. Internal Ear or Labyrinth.—This is composed of the cochlea, the semicircular canals, and the vestibule. [In the following figure there is a magnified view of the labyr- inth : (Fig. 13.) It consists of the middle portion, called the vestibule, V, from which arise the three semicircular canals, X Y Z. To the low- er side of the vestibule is attached a spiral canal, resembling the shell of a snail, called the cochlea, and marked K. The letter 0 points out the foramen ovale, and R the foramen rotundum. All these bony cavities are lined with a very delicate membrane, called the membranous labyrinth, and are filled with a thin gelat- inous fluid, formerly called the fluid of Cotunnius, who first de- scribed it: it has been recently termed the perilymph by M. Breschet. The membranous labyrinth floats in the perilymph, *nes auditory nerve being expanded upon it. The fenestra ovalis and the foramen rotundum, 0 and R, are covered with a mem- brane, and open into the cavity of the tympanum, the former haymg the bone of the stapes attached to it, as seen in figure 11, at x. The following figure, which is on a still larger scale, is taken from Breschet. SENSE OF HEARING. The osseous labyrinth is laid open, so as to show the parts it encloses, more particularly the membranous labyrinth, floating in the perilymph. The cochlea is seen to consist of the spiral con- volutions of a double tube, or, rather, one tube separated into two compartments by a partition, L L, called the lamina spiralis. These compartments are called the scales of the cochlea. One of these compartments arises from the vestibule* and the other commences at the inner side of the membrane, which closes the foramen rotundum. All these cavities of the internal ear are contained in a very hard bone, called, from this circumstance, the os petrosum. On the next page is a view of the membranous labyrinth removed from the bony cavity represented in the last figure, and in a cor- responding position, the same letters indicating the different parts in both figures. By comparison, the correspondence between the two figures is readily recognised. XYZ correspond to the semicircular canals; each present at their origin from the vestibule a considerable dilatation, termed an ampulla, marked AAA. X and Y are united. U S is the membranous vestibule, which is not an exact representation of the osseous cavity. It consists of two distinct sacs, opening into each other, of which U is called the sacculus vestibuli, the median sinus, or utricle; the other, marked S, the sacculus. They contain within a small mass of white calcareous matter, resembling powdered chalk, as it were suspended by numerous nervous filaments arising from the accous- stic nerves G N. This is observed in all the mammalia, and is no doubt important in the function of hearing. G is the anterior 84 FUNCTIONS OF RELATION. (F.g. 15.) trunk of the auditory nerve, N the posterior trunk, D the portio dura; K is a branch of the auditory nerve.] The fluid of Cotunnius is very near to the cephalo-spinal fluid at the orifice of the internal auditory passage; but it does not ap- pear that these two fluids communicate : at least my researches on this point have not led to this result. Auditory Nerve.—This nerve arises from the fourth ventricle of the brain; it enters into the labyrinth by foramina at the bot- tom of the meatus auditorius internus. Having arrived at the vestibule, it is divided into several branches, of which one remains in the vestibule, another enters the cochlea, and two are distribu- ted through the semicircular canals. The manner in which these different branches are arranged in the cavities of the internal ear has been described, with great care, by Scarpa. It would not be proper to enter here into a more minute detail. In terminating this very concise description of these parts, it will be proper to remark, that the internal and middle ear are traversed by several nervous filaments, which probably have some influence in the function of hearing. For example, the facial nerve passes through a canal hollowed out from the os pe- trosum. In this canal it receives a filament of the vidian nerve, and it supplies the cord of the tympanum, which is spread over this membrane. Many other anastomoses are likewise seen in the ear, to which the attention of anatomists has been called by M. Ribes, M. Jacobson, and M. Breschet. Recent experiments have taught us that the ear, as regards its sensibility, presents physiological circumstances analogous to those of the eye. The membrane which lines the auditory passage possesses extreme sensibility; this is very apparent at the en- trance of this passage. The slightest contact of a foreign body excites vivid pain; physicians have always noticed the exquisite sensibility consequent upon inflammation of this part. From this, it is very probable that the sensibility of the tympanum is still SENSE OF HEARING. 85 more exquisite, and that it would be at its maximum in the cavi- ties of the labyrinth. But this is not the case: as in the eye, the greatest sensibility exists about the exterior part of the apparatus. This property is very obtuse about the tympanum, and the audi- tory nerve may be touched, pricked, and torn in animals, without any apparent indication of sensibility. In this respect it is in striking contrast with the fifth pair, which may be said to be in contact with the auditory nerve at its origin, which cannot be even slightly touched without producing the most acute pain. In this respect the nerve of hearing resembles that of vision. Mechanism of Hearing. Use of the External Cartilage of the Ear.—It collects together the sonorous rays, and directs them towards the meatus audito- rius externus; this it more effectually does from its size and elas- ticity, and from its being detached from the head and directed forward. Boerhaave pretended to have proved, by an elaborate calculation, that all the sonorous rays which fall upon the exter- nal surface of the cartilage are necessarily conducted towards the auditory opening. This assertion is, however, evidently incor- rect, at least in some individuals, because, in some instances, the antehelix is more prominent than the helix. As all the rays are to be directed towards the concha, what will become of those that fall on the posterior part of the antehelix in these cases ? It is much more probable that the external cartilage, from its great elasticity, which may, perhaps, be somewhat modified by the intrinsic muscles, is capable of entering into vibrations through the influence of the sonorous undulations impressed upon the air. With respect to the inequalities of its surface, it appears from M. Savart that, according as a membrane is or is not parallel to the surfaces of bodies which vibrate near it, its oscillations are more or less distinct, parallelism being the most favourable circum- stance. This cartilage, however, is not absolutely necessary to the function of hearing; for in man, and some animals, it may be removed without the hearing being impaired for more than a few days. Uses of the Meatus Auditorius Externus. — This transmits sound to the membrana tympani, like any other tube, partly by its walls, and partly by the air contained in it. The hairs which are placed at its entrance, and the cerumen, prevent the introduction of foreign bodies, such, for example, as grains of sand, dust, or insects, &c. Uses of the Membrana Tympani.—This membrane receives the sound transmitted to it through the auditory opening. It separates the meatus auditorius externus from the tympanum. It is stretched tight, is thin and elastic, and of a uniform thickness. It is therefore thrown into vibrations by the sonorous undulations conducted to it by the air or its walls. But, from a very simple experiment of M. Savart, it appears that it is especially the air which puts it in vibration. 86 FUNCTIONS OF RELATION. This learned philosopher placed at the upper part of a truncated cone, made of paper, a delicate membrane, which closed the open- ing, very much, as the membrana tympani closes the auditory pas- sage. He then produced sounds »ear the walls, exterior to the cone; the membrane vibrated but little. But if he produced the same sounds at the base of the cone, so that they were transmitted to the membrane by the interior air, the vibrations were much more distinct, even at the distance of 100 feet. The mode of insertion of the muscles of the malleus into this little bone, and of its attachment to the membrana tympani, indicate clearly that it has different degrees of tension. It would be ab- surd to suppose that this little membrane places itself in unison with the innumerable sounds that our ears perceive. But it is more than probable that in certain cases it is stretched by the in- ternal muscle, and in others relaxed by the anterior muscle of the malleus. Heretofore these have been merely conjectures, but some experiments of M. Savart appear to have unveiled the truth. When a thin membrane is stretched very tight, it vibrates with difficulty; that is, the motions of the vibrating parts are very slight. It is the reverse when the membrane is relaxed; and as it is proved directly by experiment that the membrana tympani in place vibrates in consequence of the sonorous undulations which reach its surface, it cannot be doubted that, the more it is stretched, the less will be the extent of its vibrations. It is highly probable, therefore, that it is relaxed for weak or agreeable sounds, and tightened for intense or disagreeable sounds. An opening made into this membrane does not very essentially impair the hearing.* As it is dry and elastic, it is peculiarly adapted to the transmission of sound to the air contained within the tympanum, and to the chain of small bones. The cord of the tympanum will necessarily participate in the vibrations, and transmit to the brain certain im- pressions. The contact of a foreign body with this membrane is exceedingly painful; a violent noise also occasions severe pain in this part. The membrane of the tympanum may be torn, or even entirely destroyed, without the hearing being essentially impaired. Uses of the Cavity of the Tympanum.—Its principal use is to transmit to the internal, the sounds which it has received from the external part of the ear. This transmission of sound by the tym- panum takes place, first, by the chain of small bones, which acts particularly on the membrane of the foramen ovale ;f second, by * For the various opinions which have been formed concerning this membrane, see the works of Haller, vol. v. t We are ignorant of the use of those motions which are produced by the chain of small bones. However, as all these little bones are united together, the first in contact with the tympanum and the last with the fenestra ovalis; as, besides, the malleus can move itself, it appears to me it was indispensable, to prevent laceration, that the chain should be com- posed of a number of pieces movable upon each other. Again, it appears to me that when the malleus is drawn within, the motion extends to the stapes, which compresses the fluid contained within the labyrinth; and from this it must result, that the amplitude of the os- cillations of the membrane of the fenestra rotunda will become less. In a word, I believe that the chain of small bones is to the ear what the sounding part is to the violin. The loss of these bones, except the stapes, does not necessarily occasion deafness; we have re- marked, however, that those individuals who are in this situation only preserve this sense for two or three years. SENSE OF HEARING. 87 the air which fills it, and which acts upon the whole of the os pe- trosum, but especially upon the membrane of the foramen rotun- dum ; third, by the vibration of its walls. There appears to be no doubt that one of the uses of the tympanum is to keep before the fenestra rotunda a peculiar atmosphere, the properties of which are nearly constant, inasmuch as this small mass of air is preserved continually at the same temperature by the surrounding bloodvessels. Without this precaution, the membrane of the fe- nestra rotunda Would deteriorate soon, which must happen when the membrana tympani is freely perforated. Use of the Eustachian Tube.—This serves to admit the exter- nal air, so that the pressure on both sides of the membrana tym- pani being equal, of course no obstacle is offered to the vibrations of the membrane, by which sound is transmitted to the internal parts of the ear. The obliteration of this tube is a frequent cause of deafness. It has been supposed that this tube assists in con- ducting the sound to the internal parts of the ear, but this is a mistake, there being nothing to support the assertion. It allows the air to escape from the tympanum when the atmosphere has been violently agitated by a loud noise, and afterward admits it to.this part, and to the mastoid cells. The air in the tympanum, being very much rarefied from the heat of the body, diminishes the intensity of the sound which it transmits. Uses of the Mastoid Cells.—This is a point which is not well ascertained. It is supposed that they assist in augmenting the in- tensity of the sound which arrives at the tympanum. If they pro- duce this effect, it must be rather by the vibration of the laminae which separate the cells, than by that of the air which they con- tain. Sound may reach the tympanum otherwise than by the meatus auditorius externus. The sounds which strike upon the bones of the head may be directed towards the temporal bone, and the percussion thus arrive at the ear. We all know how dis- tinctly the noise arising from the machinery of a watch is per- ceived by placing it in contact with the teeth. Uses of the Internal Ear. We are but little acquainted with the functions of the internal ear. We suppose that the sonorous vibrations are propagated in various ways, but principally by the membrane of the fenestra ovalis, that of the foramen rotundum, and by the internal parietes of the tympanum, and that the fluid contained within the cavities of the internal part of the ear, sometimes called the fluid of Cotun- nus, must receive vibrations, which it transmits to the auditory nerve. We may likewise suppose that this fluid performs the ex- tremely important function of breaking the impulse of very in- tense vibrations, which would otherwise essentially injure the auditory nerve. It is probable that, in this case, the fluid flows back into the aqueducts of the cochlea and vestibule, which, ac- cording to this view, have considerable analogy in their functions with the eustachian tube. 88 FUNCTIONS OF RELATION. The external scala of the cochlea must receive vibrations, principally, by the membrane of the foramen rotundum; the ves- tibule, by the extremity of the chain of small bones; the semi- circular canals, by the walls of the tympanum, and perhaps by the mastoid cells, which are often prolonged beyond these canals. We are, however, absolutely ignorant of the precise share which each of the internal parts of the ear take in performing the func- tion of hearing. The osseo-membranous partition which separ- ates the two scalae of the cochlea has given rise to an hypothesis which no one believes at the present day. Action of the Auditory Nerve. This nerve receives impressions and transmits them to the brain, which perceives them with a greater or less degree of ex- actness in different individuals; but this action is itself influenced by the fifth pair; when the latter nerve is divided or diseased, the hearing is weakened, or even abolished. Many persons are said to have a false ear, that is, they are incapable of accurately dis- tinguishing sounds. We cannot explain the action of the auditory nerve, nor that of the brain in hearing, but many observations have been made on this function. A sound, to be distinctly perceived, must range within certain limits; if it be too violent, it gives us pain ; if too weak, it causes no sensation. We may perceive a great number of sounds at a time. Appreciable sounds combined, and succeeding each other in a certain manner, are a source of agreeable sensations. There is one art, the object of which is to arrange sounds in such a man- ner as to produce this effect; this art is music. . To an ear so or- ganized as to be able to appreciate it, music is undoubtedly the first of arts, for there is no one that is a source of such vivid and delightful sensations, that excites more enthusiasm, or leaves be- hind it deeper or more agreeable recollections. Certain com- binations of sounds, on the contrary, cause disagreeable sen- sations. Very sharp sounds wound the ear, and those that are very intense and grave lacerate the membrana tympani. The absence of the fluid of Cotunnus from the cavities of the internal ear destroys hearing. When a sound has been long continued, we often think that we continue to hear it even after it has ceased. As persons born blind have had their vision restored at an age when they could describe their sensations, so those born deaf have acquired the sense of hearing at an age when they could comprehend the immense advantage of acquiring a new sense. Science possesses at present many examples of this. They are not less interesting in a physiological than a philosophical point of view. Such is the following history, the authenticity of which has been established by the Academy of Sciences of Paris. Louis-Honore Tresel, aged ten years, born at Paris, of poor parents, was born deaf; he could not hear the loudest sounds. His physiognomy had little expression; he dragged his feet, his gait was unsteady, and he was incapable even of using his hand- SENSE OF HEARING. 89 kerchief. Hearing was restored to him by means of an operation invented by a blind man, who, tired of his situation, and of the useless attempts of medical men to relieve him, succeeded in cu- ring himself. This operation consists in injecting air and various liquids into the tympanum through the eustachian tube. The first days that followed the development of his sense of hearing were to Honore days of delight. All sounds, noises even, caused him ineffable pleasure, and he sought them with avidity. He was thrown into a sort of ecstasy on hearing a musical snuffbox. But it required some time for him to perceive that speech was a means of communication. Still he did not at first attend to the sounds, "but to the motion of the lips which accompanied them, and to which before he had paid no attention. For several days he be- lieved that a child of seven months spoke, because he saw it move its lips. He was made acquainted with his mistake, and from that time he began to perceive that it was the sounds that were important, not the motion of the lips which accompanied them. Hearing a magpie pronounce some words, he at once concluded that all animals possessed the power of speech, and tried to make a dog to which he was much attached speak to him. He had re- course to violence to make him say " Papa ! give me some bread," the only words he could pronounce himself. The loud cries of the animal frightened him, and he gave up the singular undertaking. A month passed; and still Honore remained nearly at the same point, absorbed by his sensations and his new remarks; he could not get hold of syllables which form words. It required a period of nearly three months to comprehend words with several sylla- bles, and the meaning of some simple and short phrases. It re- quired also a long time to recognise the direction of sound. A person having concealed himself in a chamber in which the child was sitting, called to him: it was with great difficulty he suc- ceeded in finding the place from which the voice came.—(See the end of this case in the article on the Relations of Hearing and the Voice). Action of both Ears. We receive two impressions from sound, but only perceive one. It has been said that we never use but one ear at a time, but this is incorrect. It is true, that when sound arrives directly at one ear, it is received with more facility by that, and more imper- fectly by the other, and in this case we only use one ear. When we wish to listen attentively to sounds which we fear to lose, we place ourselves in a situation that the sonorous rays may enter directly into the concha of one ear; but when we wish to deter- mine from what%oint sound proceeds, and in what direction it comes, we are obliged to use both ears, because it is only in com- paring the intensity of the two impressions that we are able to distinguish the side from which the sound comes. If, for exam- ple, we* stop one ear, and another person makes a slight noise at some distance, it will be impossible for us to determine the di- 90 FUNCTIONS OF RELATION. rection of the sound, though we should succeed every time with both ears. Sight greatly assists us in judging of sounds, for in profound darkness, even with both ears, it is often impossible to decide from what point a noise comes. Sound also enables us to judge of the distance by which we are separated from bodies which produce it. But, in order that our judgment may be correct in this case, it is necessary that we should be familiar with such sounds, otherwise our judgment will be always erroneous. In this case, our judgment is formed on the following principle, viz., that a very intense sound comes from a neighbouring body, and a very weak sound from a distant body. If it should happen that the intense sound comes from a distant body, and the weak sound from a near one, then we fall into an error of hearing. Generally, we are easily deceived in judging of the distance from which sound proceeds ; here, too, vision and reason materially assist our judgment. The different degrees of convergence or divergence in the sonorous rays do not appear to influence hearing, nor do we modify the direction of the sonorous rays, but to make a greater number enter into the ear. This is the effect produced by hear- ing trumpets which are used by the deaf. It is sometimes neces- sary to diminish the intensity of sounds; in this case we place a soft inelastic substance in the meatus auditorius externus. Pathological Tendencies. [Though there is a striking analogy in the manner in which sensation and the senses are executed, yet that they are not iden- tical. Violence inflicted on the sentient extremities of the nerves of sensation causes an exaggeration of their normal action, which is pain. But this effect is not necessarily produced in the optic nerve on wounding the retina, and the remark holds equally good with respect to the auditory nerve. The apparatus of hearing is simple, very securely placed, and much less prone to disease than that of vision. Its morbid con- ditions, however, are much less within the control of art. Little has been accomplished by modern science in this respect. The cerumen sometimes becomes inspissated, and accumulated in such quantity as to close up the external opening, and cause deafness. Perhaps the most common disorder of this apparatus is obstruc- tion of the eustachian tube. Catarrhal affections, which are so common in all climates and classes of persons, are generally at- tended with more or less inflammation of the posterior fauces. The inflammation is apt to extend up the lining of the eustachian tube, and from the consequent tumefaction or morbid secretions the tube becomes obstructed, and the air confined i^pthe cavity of the tympanum. Thus the free oscillatory movements of the tympanum are impeded, and deafness produced. On closing the nose and mouth, and making a forcible expiration, while the eustachian tube is clear, the air is felt to impinge upon the membrana tympani. SENSE OF HEARING. 9] We are thus enabled to determine with considerable certainty when the deafness arises from obstruction of this tube. There are two remedies which have been much practised in modern times for deafness arising from this cause, founded on the physiological facts referred to. The one consists in puncturing the membrana tympani; the other, and more modern operation, proposed by M. Deleau, of Paris, in dilating the obstructed eustachian tube by in- jecting into it air, warm water, and other bland fluids. Inflamma- tion of the lining membrane of the external ear is a common and painful disorder, especially in childhood, often coming on peri- odically. It frequently commences with exquisite pain and in- tolerance of sound; in a short time a purulent discharge occurs, accompanied with relief to the pain, and as the discharge gradually subsides the health is restored. In some cases the inflammation puts on a chronic form, and is attended with thickening of the membrana tympani; in others, there is ulceration of the mem- brane and destruction of the small bones, which are discharged through the external ear; in both cases, deafness is produced. Not unfrequently the purulent discharge from the external ear, the common termination of inflammation of the lining membrane, sud- denly ceases, and is followed by return of the pain and great sensi- bility to sound. In these cases of relapse, the inflammation is very apt to extend through the bony structure to the textures of the brain. This organ also necessarily sympathizes in all the changes which occur in the encephalon. In some cerebral affections, its susceptibilities are so exalted as to be painfully affected with the weakest sound; in others, so depressed as to be insensible to the loudest. The state of its functions thus constitutes one of the best guides in many acute diseases for determining the pathological condition of the brain. In acute inflammation great morbid sensi- bility to sounds and tinnitus aurium are common symptoms ; while tumours of the brain, effusions of serum or blood, are indicated by deafness in one or both ears. There is, however, but little sym- pathy between the ears and the other important organs.] Modification of Hearing by Age. The ear is formed very early in the foetus. At birth, the in- ternal ear and small bones are nearly the same as at any period of life, but the parts which belong to the middle and external ear are not in a condition to act, which constitutes an essential dif- ference between the eye and ear. The external cartilage is com- paratively very small and soft, of course possesses but little elas- ticity, and is, therefore, but imperfectly prepared to perform the function to which it is destined. The parietes of the external passage are in a similar state ; the membrana tympani is very ob- lique, forming, in some measure, the upper part of the canal, and is therefore badly arranged to receive the sonorous rays. All the external part of the ear is covered with a soft whitish matter, which obstructs its functions. The cavity of the tympanum is also proportionally small, and, instead of air, contains a thick mu- 92 FUNCTIONS OF RELATION. cus. The mastoid cells do not exist. But, as age advances, the auditory apparatus acquires that arrangement and perfection which we have described in the adult. In old age, the changes that take place in the physical structure of the ear are so far from being unfavourable, as happens in the eye, that they appear, on the contrary, to improve it. All the parts become harder and mory elastic; the mastoid cells extend themselves through the os petrosum, and surround, on all sides, the cavities of the internal ear. The loudest noises have no sensible effect upon newborn in- fants, but, after some time, they seem to distinguish sharp sounds; these are the sort of sounds generally made use of by nurses to attract their attention. It is a long time before an infant judges correctly of the intensity or direction of sounds, and especially before he attaches any meaning to articulate sounds. As he pre- fers the most vivid light, so in the same manner he is pleased, for a long time, with sounds that are loud and sharp. But, although the. physical structure of the auditory apparatus becomes more perfect in old age, it is, nevertheless, certain, that the hearing be- comes more imperfect, even at its first approach, and that there are very few old men who are not more or less deaf. This ap- pears to arise from a diminution of the humour of Cotunnus, and a progressive loss of sensibility in the auditory nerve. CHAPTER V. SENSE OF SMELL. There are many bodies in nature which suffer particles of ex- treme tenuity to escape from them, which diffuse themselves in the atmosphere, and are carried, by this vehicle, to a great dis- tance. r These particles constitute odours. One of the senses is destined to recognise and appreciate these particles, and thus an important relation is established between animals and them. Those bodies, the particles of which are fixed, are called inodorous. There is a great difference among odorous bodies in the man- ner in which they develop their odours. Some do not suffer them to escape, except when they are heated, others when they are rubbed; some exhale weak odours, others only those which are strong. Such is the tenuity of these odorous particles, that a body may exhale them for a long time without altering, sensibly, its weight. Every odorous body has a peculiar odour. As these bodies are very numerous, it has been attempted to classify them, but all these attempts have heretofore proved fruitless. We can only distinguish odours into weak and strong, agreeable and disagree- * sense of smell. 93 able. We speak, however, of a musklike odour, aromatic, and fetid odours, &c. They are likewise sometimes distinguished into fugitive and tenacious. For the most part, however, we can only designate them by comparing them with that of some known body. Nutritious, medicinal, and even poisonous qualities have been attributed to odours; but, in such cases, these opinions seem to have been formed by confounding the influence of odours with the effects of absorption. A man who pounds jalap for some time will be purged, as if he had taken its substance into his stomach. This effect cannot be properly referred to the effect of odour, but to the fine particles of the jalap which are floating in the air, and which are thus introduced into the circulation, either with the sal- iva, or the air which he respires. It is to the same cause to which we must attribute the intoxication of persons exposed for some time to the fumes of spirituous liquors. The air is the ve- hicle by which odours are generally transported to a distance, but they are also produced in a vacuum. There are some bodies which dart forth their odoriferous particles with a considerable degree of force; but this subject has not received the attention which it deserves. It has not been fully ascertained if odours ob- serve, in their progress, anything analogous to the convergence and divergence, reflection and refraction of luminous rays. Odours attach themselves to, or combine with, many fluids, as well as many solid bodies; a method which is often taken to preserve them for a long time. Liquids, vapours, gases, and many solid bodies, when reduced to an impalpable, or even coarse powder, have likewise the property of acting upon the organs of smell. Apparatus of Smell. The olfactory apparatus may be compared to a sort of sieve, placed in a spot over which the current of air that is introduced into the chest in respiration passes, and which is destined to de- tain all the foreign bodies which may happen to be mixed with the air, particularly odours. This apparatus is extremely simple. It differs essentially from that of vision or hearing in this, that we do not find before the nerve any parts which are placed there to modify the physical effects of the excitant, the nerve being, in a great measure, naked. The apparatus is composed of the pituitary membrane which covers the nasal cavities, of the membrane which lines the sinuses, and of the olfactory nerve and different filaments of the nerve of the fifth pair. [The following is a vertical and longitudinal section of the hu- man nostril. The olfactory nerve is seen passing through the cribriform plate of the ethmoid bone at O, to be distributed to the pituitary membrane which covers the nasal passages and cells. Several of these cells are seen, as the sphenoidal sinus S, the frontal sinus F, and one of the ethmoidal cells C. N is the nasal bone; P the I 94 FUNCTIONS OF RELATION. (Fig. 16.) palate; E the mouth of the eustachian tube; T T the cornets, or turbinated bones.] The Pituitary Membrane.—This covers the whole extent of the nasal fossae, increases very much the thickness of its cornets, and is prolonged beyond their edges and extremities in such a manner that the air cannot traverse the nasal fossae, except by very narrow and lengthened passages. This membrane is thick, and adheres tenaciously to the bones and cartilages to which it is attached. Its' surface presents an infinite number of small projec- tions, which are considered by some as nervous papillae, but have been supposed by others to be mucous cryptae; they are, howev- er, very vascular. These projections give to the membrane a velvetlike appearance. The pituitary membrane is smooth and soft to the touch, and receives a great number of bloodvessels and nerves. The passages which the air passes through to arrive at the back part of the mouth deserve attention. They are three in number, and are divided by anatomists into inferior, middle, and superior passages. The inferior is by far the largest, longest, and least oblique and tortuous; the middle is narrower, nearly as long, and deeper from above, downward; the superior is much the shortest, and most oblique, and narrowest. It is also proper to add to these passages, the very narrow interval which separ- ates the septum of the nostrils, through its whole extent, from the external walls. Such is the extreme narrowness of all these ca- nals, that the least swelling of the pituitary membrane renders the passage of the air through the nasal fossae difficult, and sometimes impossible. The two superior canals communicate with cavities, which are considerably spacious, hollowed out of the bones of the head, and are called sinuses. They are the maxillary, pala- tine, frontal, and sphenoidal sinuses. Those which are found in the thick part of the ethmoid bone are sometimes distinguished by the name of cellular ethmoidales. SENSE OF SMELL. 95 These sinuses do not communicate with any others than the two superior canals. The frontal and maxillary sinuses, and the anterior cells of the ethmoid bone, open into the middle passage; the sphenoidal and palatine sinuses, and the posterior cells of the ethmoid bone, open into the superior canal. These sinuses are covered with a thin, soft, and apparently mucous membrane, loosely attached to their walls: it secretes, in greater or less abundance, a substance called nasal mucus, which is continually spread over the surface of the pituitary membrane, and appears to be useful in smelling. A considerable extent of these sinuses is always found where this sense exists in great perfection. This is, at least, one of the most positive results of comparative physi- ology. The Olfactory Nerve.—This arises by three distinct roots from the posterior, inferior, and internal part of the anterior lobe of the brain. In passing towards the cribriform plate of the ethmoid bone, it is of a triangular shape; here it becomes suddenly en- larged, and is then divided into a great number of small filaments, which are ramified over the pituitary membrane, principally at the superior part of this membrane. Like the nerves of vision and hearing, the olfactory is insensible to compression, pricking, &c, and even the contact of bodies the odour of which is strong. It is important to remark, that the filaments of the olfactory nerve have never been traced on the inferior cornet, or spongy bone, on the internal face of the middle, nor any of the sinuses. The pituitary membrane not only receives the nerves of the first pair, but receives also a great number of filaments arising from the internal face of the sphenopalatine ganglion; these filaments are distributed over the inferior parts of the membrane. It is supplied also by the ethmoidal filament of the nasal nerve, and receives from it a large number of small filaments. The mem- brane which covers the sinuses receives also some small nervous The nasal fossae communicate externally through the nostrils, . the form, magnitude, and direction of which vary in different in- dividuals. The interior of the anterior nares is garnished with hairs, and their dimensions are increased and diminished by the action of certain muscles. The nasal fossae open into the pharynx by the posterior nares. Mechanism of Smell. The apparatus of smell presents some striking differences from those of vision and hearing. In the latter, the general sensibility is distinct, as regards its seat, from the special sensibility. Thus, the conjunctiva presents the one and the retina the other. In the ear, the meatus auditorius externus exercises the first, and the au- ditory nerve the second. If the two properties exist in the pitui- tary, they are much more difficult to distinguish. It appears, however, that these two properties are sometimes isolated. Some individuals are destitute of the sense of smell, though the pituitary 96 FUNCTIONS OF RELATION. membrane is exceedingly sensitive to the contact of foreign bod- ies, so as to be able to distinguish their physical properties, as, for example, different kinds of tobacco. Experiment has demonstrated to me that the general sensibility of the pituitary membrane ceases on the section of the fifth pair of nerves. As soon as the division is made, contact, pricking, or the application of corrosive agents, cease to produce any effect upon the sensibility of the membrane. In this respect, then, it resembles the conjunctiva. But, what is equally remarkable, is the entire loss of sensibility to the most penetrating and pungent odours, as ammonia, the acetic acid, &c. It thus appears that the olfactory nerve in this respect resembles the optic and auditory nerves: it can only act while the integrity of the fifth pair is pre- served. The following fact differs still more from the common- ly-received opinions respecting the functions of the first pair of nerves. I destroyed these two nerves in a dog; I then presented to the animal strong odours. He perfectly perceived them, and acted as under ordinary circumstances. I endeavoured to ascertain the same thing with respect to weak odours, as the aliments ; but I could not arrive at results sufficiently positive to affirm that these odours acted upon the nose of the animal. It would thus seem possible that the olfactory nerve is not the true nerve of smell, and that the sensibility*to odours is confounded with the general sensibility in the same nerve. (See Jour, de Physiologie, tome iy.) Many pathological »facts, which would have passed unno- ticed before the publication of these experiments, have since con- firmed these results. Cases of individuals have been observed in whom the olfactory nerves were completely destroyed, have pre- served the sense of smell, taken snuff with pleasure, and distin- guished its different qualities ; complaining also, like others, when exposed to disagreeable odours.* On the other hand, in cases where the fifth pair of nerves were destroyed, although the olfac- tory remained unchanged, the individual had lost not only the sense of smell, but also the sensibility of the pituitary membrane. May we not say that these authenticated cases, collected in the public hospitals of the capital, are the exact repetition of my ex- periments 1 and do they not render the results still more prob- able ? The sense of smell is exerted at the moment that the air trav- erses the nasal fossae in its passage to the lungs. It is very rare that we can perceive any odour in the air at the moment it es- capes from these organs, though this is sometimes observed, es- pecially in certain organic affections of the lungs. The mechanism of smell is extremely simple: it is only neces- sary that the odoriferous particles should be stopped by the pitui- tary membrane, especially in those narrow passages where it receives the filaments of the olfactory nerve. As it is precisely at the superior part of the nasal fossae, where the passages are the * See Jour de Physiologie, tome v., case, of M. Berard, communicated by M. Beclard. SENSE OF SMELL. 97 narrowest, that they are the most covered with mucus, it is prob- able that this is also a spot where a great portion of the odorifer- ous particles are stopped. It is easy to understand the use of this mucus ; its physical properties appear to be such, that it has a much greater affinity for the odoriferous particles than for the air. It therefore separates them from this fluid, and retains them upon the pituitary membrane, where they produce the sense-of smell. It is very important, in the exercise of this function, that the nasal mucus should preserve the same physical properties: every time they are changed, as happens in the different sta- ges of coryza, the sense of smell is either lost or essentially im- paired.* From what has been said of the distribution of the olfactory nerves, and the branches of the fifth pair, it is evident that odours, when they come to the superior part of the nasal cavities, will be more easily and vividly perceived. It is for this purpose that we modify inspiration, so that the air shall be directed upon this point, when we wish to perceive vividly or accurately the odour of a body. It is for the same reason that those who take snuff en- deavour to place this substance towards the upper part of the na- sal fossas. It would seem that the internal surfaces of the cornets are extremely well arranged to stop the odour at the moment that the air passes through; and, as their sensibility is very great, we are induced to believe that they assist in the function of smelling, although the filaments of the first and fifth pairs of nerves have never been traced upon them. Physiologists are not agreed as to the precise use of the nose in smelling; it appears intended to direct the air charged with the odorous particles towards the superior part of the nasal fossae. Persons whose noses are deformed, especially flattened, and those who have small nostrils, directed forward, have, generally, the sense of smell very imperfect. The loss of the nose, by disease or by accident, causes nearly an entire loss of this sense. Ac- cording to the interesting remarks of M. Beclard, we may restore the use of this sense, in individuals who are in this situation, by fitting an artificial nose. It has been supposed that the use of the sinuses, for the most part, consists in supplying the nasal mucus. But there are other uses which may be attributed to them, viz., to serve as a depot of the air charged with the odorous effluvia, and to increase the surface to which it may be applied. But all these opinions must be considered doubtful. It is certain, at least, that these cavities are not well fitted to receive the impression of odours. Diseases have proved this in man, and direct experiments on animals give the same result. Vapours and gases appear to act in the man- ner of odours on the pituitary membrane; the mode, however, is * This is the explanation given in the School of Medicine in Paris. It seems at first satisfactory, but, on a nearer examination, it will be found to rest on many assumed facts, e. g., the affinity of the nasal mucus for odours, the deposition of the odorous particles on the pituitary membrane, &c. 98 FUNCTIONS OF RELATION. probably somewhat different. Bodies reduced to a coarse pow- der have also a powerful action on this membrane; their first contact is even painful; but habit changes this pain into pleasure, as we see in snuff-takers. In the practice of medicine, we have often recourse to this property of the pituitary membrane, of pro- ducing instantaneously an acute pain by the application of certain pungent odours. In speaking of the sense of smell, it is not proper to be silent concerning the hairs which garnish the nostrils: they are, prob- ably, intended to prevent the foreign bodies which float in the air from entering the nasal fossae. Their functions are very analo- gous to those of the eyelashes, and of the hairs found at the en- trance of the external passage of the ear. [This sense is connected with the digestive and respiratory apparatus. The odour of spices and other condiments, and of certain aliments, not only indicates their adaptation for diges- tion, but sharpens the appetite, gives zest to the taste, and pro- motes the chymification. Smell and taste are so intimately asso- ciated, that sometimes it is difficult to separate them. Thus we say that certain articles smell and taste alike. Smell also co- operates with taste in pointing out the unsuitableness of certain articles as aliments. The instinctive perceptions, derived from these organs, vary in different animals, according to the capacities of their digestive apparatus ; the odour and taste of the same sub- stances are obviously agreeable to some, and disgusting to others. They appear to be much more certain guides in many of the inferior animals than in man. Thus the ergot, though poisonous to man, as well as other animals, when mixed with farinaceous substances, does not impart a disagreeable taste or odour to us, while many of the inferior animals will rather die of hunger than taste it. In some animals, smell is the predominant sense, its extent of action surpassing that of the eye or the ear in assisting it in escaping from its enemies or seeking its prey. The carniv- orous birds have been particularly remarked for the great distance from which they can discover their prey, which has been attrib- uted to this sense, although at present some doubt exists on this subject. But its offices in some instances are altogether disconnect- ed with digestion, many odours being agreeable or disagreeable without exciting ideas associated with that function. It thus sometimes acts as a sentinel in guarding the organization against those agents which, by their direct action on the lungs, or in other ways, might prove injurious. The near proximity of this organ to the encephalon seems to exert an influence on its functions. Thus certain odours almost immediately cause headache, vertigo, and syncope; even asphyxia has been thus produced. In some animals, in which the sense of smell is very acute, a direct com- munication exists between the nasal passages and the lateral ven- tricles of the brain. The intimate connexion existing between the organ of smell SENSE OF SMELL. 99 and the encephalon is also shown by the effects of pungent odours in syncope. The loss of consciousness and power of deglutition often renders this the only point at which the sinking excitability of the system can be effectively approached and roused into action by the use of stimuli. The extreme disgust which certain odours in- spire, as animal and vegetable substances in a state of decomposi- tion, &c, is a salutary instinct guarding us against influences del- eterious to the organization. Like the other superadded endow- ments of man and the higher orders of animals, it is also often used as a mere luxury—a source of agreeable sensations, inde- pendently of absolute utility in the organization. It is quite ob- vious that the various details in the arrangement of the nasal passages and cavities are designed to present a large surface for the expansion of this membrane, and facilitate the contact of the air with it. Thus the greater their expansion, generally the more acute the sense of smell; the form of the head in the greyhound and pointer, and their habits, illustrate this. It would seem that the direction and force with which the odor- ous particles strike against the membrane are important circum- stances in the exercise of this sense. At any rate, when the passage of the air is obstructed by the inflammation of the mem- brane, or the nose removed, this sense is impaired or lost. This sense, though frequently impaired or lost by disease, is perhaps less liable to false impressions or illusions than either of the others. A false sensation, however, is often produced in this part by catarrhal inflammation. The membrane covering the narrow passages becoming swollen at certain points, impinges upon itself, which causes a sensation, as if mucus were accumulated in these passages. The individual is thus prompted constantly to blow his nose, which increases the irritation. When certain pungent and odorous substances are brought in contact with this membrane, they cause an excitation of the part, in consequence of which sneezing takes place. This commences with a sense of titillation in some part of the lining membrane of the nose ; then the individual makes a deep inspiration, and this is followed by a sudden convulsive expiration, during which the air is driven with great force through the narrow nasal passages, ex- pelling the mucus and any foreign substances that may have lodg- ed there. Two or three of these convulsive efforts generally fol- low each other in rapid succession. In the normal state of this membrane, this is an instinctive effort to remove some local irritant, and does not frequently occur; but in some morbid conditions, such is its irritability, that the sneezing is excited by the slightest cause, and is almost incessant. In catarrhal inflammation this is generally one of the earliest symptoms, and is usually accompa- nied with a copious but thin secretion. This also sometimes con- stitutes a prominent and distressing symptom in slight paralytic affections. In a case of partial hemi-plegia of the right side, in which the vision and audition were affected slightly, the sneez- 100 FUNCTIONS OF RELATION. ing, attended with a copious discharge from the right nostril, is incessant and most distressing. In a more complete paralysis the reverse of this exists. Sternutation, excited by a class of agents called errbines, was formerly often had recourse to in various af- ections of the head. It is, perhaps, too seldom employed in the modern practice of medicine.] Modification of Smell by Age. The olfactory apparatus is but imperfectly developed at birth. The nasal cavities and the different cornets scarcely exist, and the frontal sinuses cannot be distinguished, though there is reason to think that infants are capable of exercising this function. I think I have seen children, soon after birth, exert this sense upon the aliments which were presented to them. With the progress of age the nasal cavities develop themselves, the sinuses become formed, and, in this respect, the olfactory apparatus continues to grow more perfect until old age. The sense of smell remains until the last moments of life, excepting in those cases where there is some organic affection of the part, such, for example, as some change in the secretion of the mucus, &c, which frequently takes place. CHAPTER VI. THE SENSE OF TASTE. Taste is the impression made upon the tongue by certain bod- ies ; those substances which produce this effect are called sapid. It has been supposed that the degree of sapidity in any body might be judged of by its solubility. But there are some bodies which are insoluble, yet have a strong taste, and there are others which are very soluble that have scarcely any perceptible taste. Sapidity appears to have some relation to the chemical nature of bodies, and to the general effects which they produce on the ani- mal economy. Tastes are very various and numerous ; several attempts have been made to divide them into classes, but this has never yet been done with complete success ; at the same time, we have been rather more fortunate, in this respect, than with odours. This un- doubtedly arises from the fact, that the impressions which we de- rive from the sense of taste are less transient than those of smell. The propriety of the following distinctions among sapid bodies is universally acknowledged, viz., acrid, acid, bitter, sweet, rough, &c. There is another division of these bodies which will be admitted by every one, because it is founded upon organization ; it is that SENSE OF TASTE. 101 of agreeable and disagreeable. Animals instinctively establish this distinction. This division is also the more important, because those bodies the taste of which is agreeable are usually those that are most nutritious; and, on the contrary, those the taste of which is disagreeable, are often injurious. Apparatus of Taste. The tongue is the principal organ of taste; at the same time, the lips, the internal surface of the cheeks, the palate, the teeth, the pharynx, the oesophagus, and the stomach itself, are suscepti- ble of impressions from the contact of sapid bodies. The saliva- ry glands, the excretory ducts of which open into the mouth, and those follicles which pour out mucus into this cavity, concur pow- erfully in the function of taste. Independently of the mucous fol- licles found on the superior surface of the tongue, which have re- ceived the name of fungous papillce, there are still smaller pro- jections, the most numerous of which are called villous papillae; and still others, less numerous, which are disposed on the side of the tongue in two ranges, and are called conical papillce. All the nerves distributed on those parts which are destined to receive the impression of sapid bodies must be comprised in the apparatus of taste. Thus the inferior maxillary, and many tranches of the superior maxillary nerves, among which it is proper to mention the filaments which arise from the sphenopala- tine ganglion, particularly the naso-palatine nerve of Scarpa, the nerve of the ninth pair, the glosso-pharyngeal nerve, &c, all ap- pear to assist in the function of taste. The lingual nerve of the fifth pair is usually considered by anatomists as the principal nerve of taste ; for its filaments, they assert, may be traced to the villous and conical papillae of the tongue. 1 have myself attempted to do this, but in vain. Not- withstanding I have employed the most delicate instruments, mag- nifying glasses, and microscopes completed according to the prin- ciples of Mr. Woolaston, all my efforts have been unsuccessful. We entirely lose sight of them the moment we arrive at the ex- terior membrane of the tongue. We do not succeed better with the other nerves which are distributed over this organ. Mechanism of Taste. In order that we may exercise the function of taste perfectly, it is necessary, that the mucous membrane which covers these or- gans should be in a state of integrity, that it should be covered with mucus, and that the saliva should be poured out abundantly. When this membrane is dry, the taste is very imperfect. It is likewise necessary that these fluids should be in a natural state, for if the mucus be thick and yellowish, or if the saliva be acid or bitter, &c, the taste will be defective. Some authors assert that the papillae of the tongue are in a complete state of erection during the action of tasting ; I believe, however, that this assertion is entirely destitute of foundation. 102 FUNCTIONS OF RELATION. It is sufficient that the body be in contact with the organs of taste, in order that we may judge correctly respecting it; but, if it be a solid body, it will be often necessary that it should be first dissolved in the saliva, but this is not necessary in liquid or gas- eous bodies. It would seem that sapid bodies produce a certain chemical action upon the epidermis of the mucous membrane of the mouth; this is at least the case in some instances; e. g., vinegar, mineral acids, alkalis, a great number of salts, &c. In these cases, the colour becomes changed; sometimes it becomes white, sometimes yellow, &c. They produce analogous effects upon the dead body. It is probable that the manner in which this combination takes place has some relation to the promptitude with which sapid bod- ies act, and the duration of the impression. No satisfactory explanation has yet been given why the teeth are strongly influenced by certain sapid bodies. It appears from the researches of M. Miel,* a distinguished dentist of Paris, that this is the effect of imbibition. The experiments of this gentleman prove that the teeth imbibe promptly the fluids with which they are in contact. This extends even to the central part of the tooth, where the nerve is placed, which is a branch of the fifth; hence the sapid impression. The different parts of the mouth appear to have each a peculiar susceptibility to the action of sapid bodies ; for some more parti- cularly affect the tongue, some the teeth, and others the gums. There is another class of these bodies, the action of which seems to be almost exclusively confined to the palate and pharynx. We are indebted to Messrs. Guyot and Admyrault for the fol- lowing new and curious experiments: Experiment 1st. The anterior part of the tongue being placed in a sack of very flexible parchment, a small quantity of conserve or very sapid jelly was placed between the lips. This was moved about pressed by the lips, but no other impression was experienced than what arose from consistence and temperature. The same result was observed when the sapid substance was placed on the anterior part of the inner surface of the cheek, and of the arch of the palate, provided that neither the substance itself, nor the sa- liva impregnated with it, came in contact with the tongue. This result was verified with diluted hydrochloric acid and water sweetened with sugar. It was impossible to distinguish one of these substances from the other, no taste being perceptible from either. Experiment 2d. If we separate the cheek from the alveolar arch, and coyer it interiorly with a little acid ice, or sweetened ice, no taste is perceptible, provided we take the precautions re- specting the tongue and saliva above indicated. This experiment may be varied by placing between the cheek and the alveolar arches a soluble body like sugar or common salt, or a little ex- * This gentleman was not only distinguished by his learning, but his patriotism and courage. He fell in the glorious struggle of July, 1830. SENSE OF TASTE. 103 tract of aloes. The taste is not manifest until it deliquesces, but if we permit the saliva to spread itself to the edges of the tongue, the taste becomes very vivid. Experiment 3d. The tongue was covered as in the first experi- ment, but to a greater extent, by means of a prolongation of the parchment, which extended almost to the epiglottis. A number of pulpy substances with strongly-marked taste were swallowed, care being taken during the deglutition to place them successively in contact with all parts of the palatine arch and of the veil of the palate; it was observed that the sense of taste was only man- ifest when these substances came in contact with this last part. Experiment 4th. If the whole extent of the palatine arch be covered with a sheet of parchment, and a sapid body placed upon the tongue and swallowed, the impression thus produced is not less vivid. Experiment 5th. A fragment of the extract of aloes attached to the extremity of a stylet, and rubbed over all the parts of the pal- atine arch and the veil of the palate, gives the following results. Through the whole extent of the palatine arch, from the edges to the centre, there is no other impression than that of feeling. It is the same precisely with the uvula, the pillars of the veil of the palate, and the greater part of that organ. But at the anterior, middle, and superior part of that organ, a line below its point of insertion into the palatine arch, there is a small surface, without precise limits, not descending to the base of the uvula, but about three quarters of a line distant from it, prolonging itself, and losing itself insensibly at the sides ; this surface perceives tastes in a re- markable manner. The same instrument carried into the back part of the mouth, and applied to the posterior surface of the veil of the palate and the mucous membrane of the pharynx, demon- strates that these parts do not participate in the sense of taste. If, then, we except the part we have indicated of the veil of the pal- ate, the tongue is the exclusive seat of taste; but all parts of the mouth concur in this sense. Experiment 6th. If the tongue be covered with a piece of parchment, pierced at its centre in such a way as to correspond to the middle of its dorsal face, if we apply to this part an acidu- lated or sweetened conserve, there is no sensation of taste, even though pressed against the palative arch. The taste is only mani- fest when the saliva impregnated with it reaches the edges of the tongue. If we repeat this experiment over the greater part of the dorsal surface of the tongue, the result will be found the same. Experiment 7th. A sapid body placed before the frenum of the tongue, and compressed by the inferior surface of the organ, does not produce the sensation of taste. Experiment 8th. A piece of aloes, or a sponge soaked with vin- egar, and carried to the different parts of the tongue, gives the fol- lowing results. The whole dorsal face of the tongue does not possess the property of taste, but it is manifested as we approach 104 FUNCTIONS OF RELATION". the circumference, in an extent from one to two lines on its edges, and from three to four from the apex. Taste is perceived vividly and nearly uniformly on the edges of the tongue, to within about four lines of their anterior extremi- ty. From this point it becomes stronger to the apex, where it exists at its maximum intensity. There are some bodies which leave for a long time their taste in the mouth; this is especially the case with aromatic substances. This remaining taste is sometimes perceived over all the mouth, and sometimes occupies only one spot Acrid bodies, for exam- ple, leave their impression in the pharynx, acids on the lips and teeth; peppermint leaves an impression which exists at the same time in the mouth and pharynx. It is necessary that bodies should remain for some time in the mouth, in order that their taste may be appreciated. When they pass rapidly through this cavity, the impression which they make is almost nothing; this is the reason why we swallow quickly those substances the taste of which is disagreeable, and why, on the contrary, we allow those things to remain long in the mouth the taste of which is pleasant. When we take a substance, the flavour of which is strong and permanent, vinegar for example, we become insensible to the ac- tion of less pungent bodies. We often make use of this observa- tion to enable our patients to avoid the disagreeable taste of cer- tain medicines. We are capable of perceiving many tastes at the same time, and of distinguishing their different degrees of intensity. Thus, we are sometimes enabled to distinguish, very exactly, the chemical nature of different substances, as we see in chemists, epicures, and persons who make a business of tasting wines and other liquors. J3y these means we can sometimes form a very exact judgmenr of the chemical nature of bodies. The taste, however, never arrives at this degree of perfection but by long experience, or, rather, by a complete education. It may be inquired if the lingual nerve be the essential nerve of taste ? This question, formerly so obscure, no longer presents any difficulty: physiological experiments and pathology have completely resolved it. If the lingual nerve in an animal be divided, the tongue con- tinues to move, but it loses the faculty of taste. In this case the palate, the gums, and the internal surface of the cheeks pre- serve their sensibility; but if the trunk of the fifth pair be divided in the cranium, the perception of taste is completely lost, even as respects the most acrid and caustic substances. This total abo- lition of taste has been noticed in persons in whom the trunk of the fifth pair is compressed or altered. Everything I eat, says a patient in this state, seems to me like earth. In the sense of taste the general sensibility is confounded with the special. It is also worthy of being remembered, that the two phenomena pertain evi- dently to the same nerve. SENSE OF TASTE. 105 [There must be certain inherent qualities in the substances pre- sented to the tongue, called sapid, in order to produce the sense of taste. These qualities differ very much, both in degree and kind, in different substances. This sense is placed as a sentinel over the digestive apparatus, and indicates, with considerable certainty, those substances which are unsuitable for the action of these organs. But the tongue does not only possess the power of ascertaining the sapidity of bodies ; it has also, in a very high degree, the sense of touch and the power of voluntary motion, and, as we have already seen, is intimately associated with the organ of smell. The approach to the important series of or- gans appropriated to digestion is thus directly guarded by three of the senses, taste, touch, and smell, assisted by vision and the power of voluntary motion. We judge of the fitness of any sub- stance for food not only from its appearance, odour, and taste, but from its degree of consistency and size, by the sensation and voluntary motion of the tongue, before we introduce it into the stomach by deglutition. The tongue is not to be regarded as exclusively an organ of sense, but also as a part of the digestive apparatus. On the re- ception of food into the mouth possessing agreeable sapid quali- ties, if the individual be in health, the digestive apparatus is roused into action. The excitement of these organs is dependant not only upon the agreeableness, but the pungency of the food. If it be piquant, the appetite becomes urgent; if insipid, the reverse. The agreeableness of the taste diminishes with the repletion of the stomach; it gradually becomes insipid, and at last disgusting. The sense of smell also conspires, with that of taste, in quickening the action of the digestive apparatus. It is almost impossible to separate the action of these two senses. Those articles which are insipid are also inodorous, and vice versa. If we close the nostrils, the sense of taste is exceedingly weakened. This is often done in taking nauseous draughts, it being generally supposed that we thus merely avoid the disagreeable odour; but careful obser- vation shows that the offensive taste is also diminished. The in- timate association of these organs with the digestive apparatus is shown by the influence produced upon their functions by its dis- ordered state. Under these circumstances, the organs of taste and smell become indifferent, or even offended, by those very ali- ments that were before the most agreeable. Even the appear- ance of the tongue varies with the state of the stomach, so that we can, with considerable certainty, determine the state of the latter by inspection of the former. The accuracy of this guide has, no' doubt, been exaggerated, especially by the Broussaisan school. Still, it is, unquestionably, a most useful index in the greater number of diseases. A consideration of these appearan- ces will be found more satisfactory in connexion with the patho- logical conditions of the digestive apparatus. With respect to the action of the senses, it may be remarked, that the certainty with which they indicate the qualities of bodies 0 106 FUNCTIONS OF RELATION. varies very much in different individuals, and in the same individ- ual at different times. In the normal state of these organs, the impressions they are destined to receive are slight and imperfect, unless the attention is directed to the subject. The individual is often scarcely conscious of the numerous slighter impulses to which they are subjected. It is only when these impressions are unaccustomed, or stronger than usual, or excite certain associations, or when the individual desires to ascertain certain phenom.ena, that the action of the organs is sufficiently roused to produce their full effect. When diseased, their susceptibility is either impaired or lost, or morbidly exalted, so that the slightest impression becomes disagreeable, or painful and inaccurate. In forming our judgment respecting the qualities of bodies, where we are doubtful, we sel- dom rely exclusively upon one of the senses, but compare the im- pressions made upon each. If, e. g., it be concerning the suitable- ness of an aliment, we subject it to the action of all the senses; except, perhaps, of hearing, before we venture to introduce it into the stomach. Like the other organs, the senses improve as we approach maturity, and become more acute and discriminating by suitable training and use. A landsman, on first going to sea, is astonished at the promptitude with which sailors discover a dis- tant sail, and the accuracy of their judgment as to the character of the stranger, and the course she is steering, while it appears to him, perhaps, an obscure speck in the horizon. Those varieties of the human species which possess dark complexions have been thought to exhibit greater acuteness of the senses than the Euro- pean. This opinion is, probably, founded on the habits of all wan- dering and barbarous tribes who live by the chase and war, which necessarily lead to the constant exercise of the senses, as on them their safety, and even existence depend. It is astonishing to what a degree of perfection they attain. The North American savage will pass through forests he had never seen, in a given direction, or follow the trail of his enemies for days, guided by marks im- ?erceptible and unappreciable to the senses of civilized man. 'alias, who was familiar with the habits of the wandering tribes of Asia, remarks of the Calmucks, " They have a fine nose, a good ear, and an extremely acute eye. On their journeys and military expeditions they often smell out a fire, and thus procure quarters or booty. They can distinguish, by smelling at the hole of a fox or other animal, whether it be there or not. By lying flat, and putting their ear to the ground, they can catch, at a great distance, the noise of horses, a flock, or a single animal that has strayed. But nothing is so surprising as the perfection of their eyes, and the extraordinary distance at which they often perceive, from inconsiderable heights, small objects, as the rising of dust, caused by cattle or horsemen, notwithstanding the undulation of their boundless steppes, and the vapours that constantly float over them. In the expedition of the Cham Ubraschi against the Ku- banians, the Calmuck force would certainly have missed the ene- my if a common Calmuck had not perceived, at the distance of SENSE OF TOUCH. 107 thirty versts, the smoke and dust of the hostile army, and pointed them out to other equally experienced eyes, though the command- er could discern nothing, even with a good glass." The loss of one sense is in some degree compensated by the improvement of those that remain. A remarkable example of this occurs in the case of Julia Brace, an inmate of the Hart- ford Deaf and Dumb Asylum, who is deaf, dumb, and blind. Such is the acuteness of her sense of smell, that she is enabled to select her own clothes from among those of upward of a hundred per- sons, after they have been washed, and is in the habit of doing so without the slightest mistake. It is evident that she is guided al- most exclusively by the smell.] Modification of Taste by Age. It is difficult to say if taste exists in the foetus; it is certain, however, that the principal organ, and the nerves which are sent to it, are fully developed. That this sense exists at the time of birth there can be no doubt, as any person may satisfy himself by rubbing upon the tongue, or even upon the lips, any bitter or sweet substance. The impressions of taste appear to be very vivid in children, as is shown by their repugnance to everything the flavour of which is strong. Taste remains in the most advanced age, though it is true that it becomes weaker, and that old persons, generally, prefer ali- ments and drinks the flavour of which is strong. But this is one of the peculiarities of their organization, which requires very ac- tive excitants for the maintenance of its powers when they have become very weak. Taste assists us in the choice of aliments ; together with smell, it enables us to distinguish those substances which are injurious from those that are useful; it is likewise the sense which enables us to form the most correct judgment of the chemical composition of bodies. CHAPTER VII. OF TOUCH. Touch is the sense which makes us acquainted with the great- est number of the properties of bodies. In consequence of its be- ing less subject to error than the other senses, and because, in certain cases, it enables us to detect it, it has been considered as the most perfect of the senses. But it will be seen that its ad- vantages have been very much overrated, both by physiologists and metaphysicians. 108 FUNCTIONS OF RELATION. Though essentially the same, we may distinguish between sen- sation and touch. Sensation is, with few exceptions, common to every part of the body, especially the cutaneous and mucous sur- faces ; it exists in all animals, while touch is evidently confined to parts particularly destined to this purpose. Touch does not exist in all animals, but it is nothing more than sensation united with muscular contraction, and directed by the will. In a word, in the act of sensation, we may be considered as being passive, but in ex- ercising the sense of touch, we are active. Apparatus of Touch and Sensation. This sense enables us to become acquainted with nearly all the physical properties of bodies. Their form, dimensions, different degrees of consistence, weight, motion, and vibration are all cir- cumstances of which we are enabled to judge with accuracy by the sense of touch and sensation. [Though sensation exists in almost all the structures, yet the ex- tremities of the fingers may be considered as more particularly the seat and organ of touch. The hand being broken up into numerous joints, and being very flexible, is well suited to explore objects by this sense. The tip of the tongue also possesses this property in a very eminent degree. Though we have no means of multiplying the power of this sense, as in hearing and vision, yet it is capable of great development; in some instances it is alleged that individ- uals have been able to distinguish certain colours by its aid.— (Begin.) Of the grosser properties of bodies, as their density, roughness, sharpness, temperature, &c, it is more direct and less liable to deception than the other senses; it depends on the integrity and continuity of the fibrous structure. This appears to be an indispensable condition. It thus constitutes a most important sentinel in protecting the organization from the various noxious influences to which it is exposed. Not only the integument, but the muscles, in many instances, receive nerves of sensation, as. well as those of voluntary motion. Hence it happens, especially in the superior extremity, which may be considered the organ of touch in man, that those two properties, sensation and voluntary motion, are intimately associated. We estimate the properties of bodies not only by the sensation which they produce upon the skin, but also by the resistance they present to the muscular ac- tion. Again, the muscular action is often guided by sensation. The effort we make in raising, grasping, holding, or crushing bod- ies is, at least, partly determined by the impression which their resistance produces upon the sensation. Thus we occasionally meet with cases of paralysis of the nerves of sensation of different parts, while the power of voluntary motion remains unimpaired. A case is related by Dr. Yelloley of a person in whom this exist- ed in the fore-arm. The contractile power of the muscles was perfectly natural, and so long as the patient looked at them she SENSE OF TOUCH. 109 had no difficulty in holding glasses, or any other common objects, but as soon as her vision was directed to any other object, the muscles, not admonished by sensation, relaxed, and allowed what- ever she held in her hand to fall to the ground. This general distribution of sensation over the whole surface is indispen- sable to the preservation of the integument. We are thus not only admonished of injurious variations of temperature, but are also prevented from subjecting any part of this organ to a long- continued pressure, by remaining for too great a length of time in the same position. After lying for a time in the same posture, the pressure made by the prominences of the bone upon the skin be- comes disagreeable, and we alter our position. We see the im- portance of this admonition in those cases where there is a loss of sensation in the skin from paralysis, such individuals being ex- ceedingly subject to ulceration, and even gangrene of the integu- ment, from this cause.] The parts destined to this sense do not alone perform this func- tion. In this respect it differs very essentially from the other senses. As in the great number of instances, however, it is the skin which receives the impressions of touch from those bodies which surround us, it is necessary to say something concerning its structure. The skin forms the envelope of the body ; it is lost in the mu- cous membranes, at the entrance of all the cavities, but it is in- correct to say that these membranes are a continuation of it. The skin is principally formed by the dermis, the texture of which is fibrous, and is of different degrees of thickness, accord- ing to the parts which it covers. It adheres to these parts some- times by cellular membrane, and sometimes by a fibrous attach- ment. The dermis is nearly always separated from the subja- cent parts by a lamina, which assists in the exercise of the sense of touch. The external surface of the dermis is covered by a solid sub- stance secreted by the skin, called the epidermis. The epidermis ought not to be considered as a membrane ; it is a lamina of ho- mogeneous substance, adhering by its internal surface to the der- mis. It is pierced by an infinite number of small holes, some of which allow the hairs to pass through, and others the cutaneous transpiration to escape, and, at the same time, they assist in the absorption which is carried on by the skin. These are called the pores of the skin. It is proper to remark, with respect to the epidermis, that it is insensible, that it does not possess any of the properties of life, and that it is not subject to putrefaction. It is constantly taken away and again replaced, and its thickness is in- creased or diminished according as the situation of the parts may require. It cannot be acted upon through the medium of the di- gestive organs. The connexion between the dermis and epidermis is intimate ; nevertheless, we cannot doubt that there is between these two 110 FUNCTIONS OF RELATION. parts a particular lamina, in which important phenomena take place. The organization of this lamina is still but little known. Malpighi supposed that it was formed by a particular mucus, the existence of which has been long admitted, and which has been called the rete mucosum, or mucous substance of Malpighi. Oth- ers have considered it, with more reason, as a network of blood- vessels.* M. Gall compares it to the cinerltious substance found in many parts of the brain. M. Guatier, in examining with attention the external surface of the dermis, observed small reddish projections, arranged in pairs. They are easily recognised when the dermis is denuded by the action of a vesicatory. These small bodies are regularly arran- ged in the palm of the hand and the sole of the foot. They are sensible, and are reproduced when they have been torn away. They appear chiefly made up of bloodvessels. These bodies have been for a long time called cutaneous papillae, but they have never been studied with care. The epidermis is pierced over their top by a small opening, by which we can observe drops of sweat to escape when the skin is exposed to a temperature a lit- tle elevated. The skin contains a great number of sebaceous follicles; it receives many bloodvessels, and a great number of nerves, particularly at those points which are destined to exercise the function of touch. We are entirely ignorant of the manner in which the nerves terminate in the skin; all that has been said of the nervous cutaneous papillae is completely hypothetical. The functions of feeling and touch are assisted by the thinness of the dermis, a temperature of the atmosphere somewhat elevated; abundant cutaneous transpiration, as well as a certain thinness and flexibility of the epidermis. When the reverse of these cir- cumstances exist, the sensibility and the touch are always more or less imperfect. Formerly physiologists supposed that all the nerves concur in feeling, and even touch. But this is not the case. Experiment shows, on the contrary, that many of the nerves do not possess this property, and in the same nerve that all the filaments do not present it. For example, the nerves which arise from the me- dulla spinalis have an anterior and posterior root. The latter alone appears to impart feeling to the organs of the trunk and ex- tremities. Mechanism of Sensation. The mechanism of sensation is extremely simple ; it is sufficient for the bodies to be in contact with the skin to enable us to form an idea, more or less exact, of their sensible properties. We are enabled to judge particularly of temperature by feeling. When bodies abstract caloric from us, we say they, are cold, and when * In those cases where vesicatories have been applied to the part some time before death, numerous vessels, very small, and filled with blood, may be distinguished on the external surface of the dermis. SENSE OF TOUCH. Ill they impart heat, we say they are warm; thus, according to the quantity of caloric of which they deprive us, or whk^h they im- part to us, we determine their different degrees of Temperature. The judgment which we form of temperature is, nevertheless, far from being accurate in relation to the quantity of caloric which our bodies»give off or receive ; we unconsciously institute a com- parison between the temperature of the surrounding atmosphere and those substances which are in contact with our bodies. If an object be ^plder than our body, but warmer than the atmosphere, it will appear warm to us, although it abstracts caloric when we touch it. This is the reason why such places as caves and wells, the temperature of which is uniform, appear to us cold in sum- mer, and warm in winter. The capacity of bodies for caloric influences also our judgment of temperature; for example, how different are the sensations caused by iron and wood, at the same temperature. A body sufficiently warm to decompose chemically our organs produces the sensation of burning. A body, the temperature of which is sufficiently low to absorb very rapidly a great proportion of the caloric of a part, produces a similar sensation; this any one may satisfy himself of by touching congealed mercury. Those bodies which have a chemical action upon the epider- mis, which dissolve it, such as the caustic alkali and concentra- ted acids, produce impressions peculiar to these bodies, which may serve to distinguish them. All parts of the skin are not endued with the same degree of sensation, so that a body applied successively on different parts of the skin will cause a series of very different impressions. The mucous membranes possess a very delicate sensibility. It seems hardly necessary to point out the great sensibility of the lips, tongue, conjunctiva, pituitary membrane, and the mucous mem- brane of the trachea, ureters, vagina, &c, &c. The first contact of those bodies, which are not naturally destined to come in con- tact with these membranes, is painful, though this effect ceases by habit. The sensation of these parts is sometimes acted upon by vapours or gases; thus, ammoniacal vapours or acids affect painfully the conjunctiva, the larynx, &c. This phenomenon is evidently analogous with smell. Mechanism of Touch. In man, the hand is the principal organ of touch; all the cir- cumstances which are the most favourable to it are there found united. The epidermis is thin, polished, and very flexible, the cutaneous transpiration is abundant, and there is likewise an oily secretion. The vascular network, called the rete mucosum, is there in an unusual quantity, and the dermis is of very inconsid- erable thickness; it receives many bloodvessels and nerves; it adheres to the subjacent aponeurosis by a fibrous attachment, 112 FUNCTIONS OF RELATION. and is sustained by adipose substance and cellular membrane, which arc very elastic. It is at the extremity, or ball of the finger, that all these arrangements exist in the highest degree of perfec- tion. The motions of the hand are easy and various, so, in a word, that this part may be applied to every body, whatever may be the irregularity of its figure. While the hand remains immo- vable upon the surface of a body, it only performs the function of sensation; it is necessary, in exercising the sense of touch, that it should move over the surfaces of bodies, in order to make us ac- quainted with their form, dimensions, &c, or to compress them, so that we may form just ideas of their elasticity, density, &c. When the dimensions of a body are very great, we employ the whole hand to examine it; if, on the contrary, the body is very small, we only touch it with the extremity of our finger. This organ is much more perfect in man than in brutes; his touch is so delicate, that it has been considered as the principal source of his intelligence. Caloric sometimes plays the same part in the sense of touch as light in vision. It makes us acquainted with the presence and certain properties of bodies, though they may be at a distance from us ; and, as happens with vision, we instinctively refer to distance the impression thus arising. From the highest antiquity, this sense has been considered more perfect than the rest, and has been described as the cause of hu- man reason. This idea is maintained at the present day, and has even been very much extended in the writings of Condillac, Buffon, and modern physiologists. Buffon, in particular, has at- tached such a degree of importance to touch, that he seems to have thought that the different degrees in which this sense was cultivated was the principal cause of the difference observed in the minds of men; he enjoins, therefore, the importance of allow- ing infants the free use of their hands.* The touch, however, has really no superiority over the other senses; and if, in some cases, it assists us in seeing or hearing, in others these senses afford it equal assistance; nor is there any reason to believe that the ideas which it excites in the brain are more vivid than those which arise from the action of the other senses. Modifications of Sensation and Touch by Age. It is probable that the foetus does not exercise this sense, at least in its more rigorous acceptation. It may be said that the first contact of the air with the skin of the new-born infant causes severe pain, which is the reason of its cries. I believe, however, that this idea is unfounded. * There is now in Paris a young artist who has no trace of fore-arms or hands. He has but lour toes to his feet, the second being wanting; yet he Is remarkable for his intelligence; he is even possessed of decided talent. He designs and paints with his feet; we may add, that these parts possess a sensibility and flexibility much more developed than is usual It is certainly surprising that one so little favoured by nature should possess taste and talent as an historical pamter. SENSE OF TOUCH. 113 Sensation and touch grow more obtuse with the progress of age. In old age they are sensibly diminished; at this period the skin undergoes changes which are unfavourable to this sense. The epidermis is no longer soft and flexible, the cutaneous transpira- tion is not abundant, the fat which before sustained the skin is absorbed, and it becomes flaccid and rugous. We can easily imagine that all these causes will impair the functions of sensation and touch, especially when we recollect that the power of re- ceiving impressions generally becomes perceptibly diminished in old age. By the exercise of this sense, it may be brought to a very great degree of perfection, as is observed in many professions. A deli- cate touch is indispensable both in a physician and surgeon. Of Internal Sensations. All the organs, like the skin, possess the faculty of transmitting to the brain impressions, when they are brought in contact with foreign bodies, or when they are compressed or bruised. They may be said, generally, to possess sensation. We must except, however, from this remark, the bones, tendons, aponeuroses, and ligaments, which in a state of health are totally insensible, and may be even cut, burned, or torn, without the brain being affect- ed by it.* It seems incredible, according to the prevailing ideas on such subjects, that many of the nerves, as well as the tendons, aponeuroses, &c, are also insensible to all mechanical excitants. This holds true with respect to the first, second, third, fourth, sixth, and the portio mollis of the seventh pair of nerves, and the branches of the great sympathetic.f—(See Expts., Journ. de Phys., t. iv.) This important fact was not known by the an- cients ; they considered all the white parts of the body as nervous, and attributed to them properties which we now know only per- tain to the nerves. It is to the experiments of Haller and his disciples that we are indebted for this useful information, which has exerted a powerful influence upon the progress of modern surgery. Indeed, before this unsuspected fact was ascertained by direct experiment, the great fear of surgical operators was wounding these white parts. At present no such apprehensions exist; this is a striking illustration of the great value of physiolo- gical experiments on living animals. How many individuals owe * I have remarked, however, frequently in my experiments, that the part of the dura- mater that forms the walls of the superior longitudinal sinus possesses undoubted sensi- bility. t The portio-dura of the seventh pair, or facial nerve, has some peculiarities in this re- spect. It does not appear to possess sensibility in itself; but if it is laid bare in a living ani- mal, it exhibits unequivocal indications of sensibility. But M. Eschriht, professor of phy- siology at Copenhagen, has proved, by many nice experiments, that if this nerve pos- sess sensibility, it depends, like all the nerves of the face, on the integrity of the/ fifth pair. This may also be inferred from an experiment made by myself, in which I cut both trunks of the fifth pair within the cranium. The whole face immediately lost its sensi- bility ; of course that of the seventh was included; but the idea of drawing this inference did not occur to me. Fortunately for science, my learned friend did so, and made the sub- ject the special object of his researches. 114 FUNCTIONS OF RELATION. their life to the confidence which this knowledge has given to the surgeon ! The fact that I had the happiness to discover, viz., that certain nerves, as well as the tendons, aponeuroses, cartilages, &c, are destitute of sensibility, will, I trust, have no less influence on the future progress of surgery. Without the intervention of any external cause, all the organs may spontaneously transmit a great number of different impres* sions to the brain. They are of three kinds. The first arises when there is a necessity that the organs should act; these may be called instinctive desires. Such are hunger, thirst, a desire to pass urine, respiration, and the venereal ap- petite. The second takes place during the action of the organs; they are often obscure, but sometimes very vivid. Of this number are the impressions which accompany the different excretions, the im- pressions which we perceive during the period of digestion; thought itself may be included among this sort of impressions. The third kind of internal sensations takes place when the or- gans have acted. To this kind belong the sensation of fatigue, varying, of course, according to the pari, affected. It is necessary to add to these three kinds of impressions, those which arise from disease ; these are very numerous, and a pro- found acquaintance with them is indispensable to the physician. All the sensations which arise from within, independently of the action of external bodies, have been designated as internal sen- sations. Their consideration was neglected by the metaphysi- cians of the last century, but their study has of late engaged the attention of many distinguished authors, particularly of Cabanis and M. Destutt Tracy; their history constitutes one of the most curious parts of ideology. Of a supposed sixth Sense. Buffon, in speaking of the intensity of those agreeable sensations which are produced by the approach of the sexes, has observed, in figurative language, that they depended on a sixth sense. The professors of animal magnetism, especially those of Germany, talk much of a sense which remains awake when the rest are asleep; that it is particularly developed in those persons who are called somnambulists, and that it gives to them the power of predicting future events. This sense, it is pretended, forms that instinct of animals by which they become acquainted with dangers which are near, and that it resides in the bones, viscera, ganglions, and the nervous plexus. To attempt to answer such reveries would be only to throw away one's time. M. Jacobson having discovered in the os incisivum of animals a particular organ, suspected that it might be the source of a dis- tinct order of sensations ; but he has given no proof of this. The faculty which bats have of directing their flight in the darkest places, has induced Spalanzani, and M. Jurine, of Geneva, SENSATIONS. 115 to think that these animals are possessed of a sixth sense; but M. Cuvier has shown that this power of conducting themselves in the dark is attributable to the sense of touch. There is, therefore, no evidence of a sixth sense. CHAPTER VIII. OF SENSATIONS IN GENERAL.* Sensations form the first part of the life of relation; they es- tablish our passive relations with surrounding bodies. This ex- pression passive, as any one will easily perceive, is true only in a limited sense; for sensations, as well as the other functions of the economy, are the result of the action of the organs, and, of consequence, are essentially active. Every substance which ex- ists is capable of acting upon our senses; we cannot know posi- tively of their existence but in this way. Sometimes they act directly upon our organs; at others, through the medium of other bodies, as light, odours, &c. The greater number of bodies act upon several of our senses; others, again, only affect one. The organs of sensation are formed of an exterior part, which exhibits physical properties in common with other bodies, and of nerves, which receive impressions and transmit them to the brain. The exterior parts of. the apparatus of vision and hearing are very complicated; those of the others are very simple. But in all, the relation between their physical condition and other bodies is such, that the least alteration in that condition causes a marked derangement of function. Nerves. The nerves, which form the second part of the instruments of sensation, are the essential organs of sense. All the nerves have two extremities ; the one is confounded with the substance of the brain, the other variously arranged in the organs. Each of these extremities has in turn been called the origin and termination of the nerves. Some say that all the nerves arise in the brain, and terminate in the organs; others, that they arise in the organs, and, by uniting, form the brain. These modes of expression are both improper, and convey very false ideas. They can be only useful in the description of the organs; but, as other expressions may easily be substituted, without at all obscuring the subject, it is desirable that they should be abandoned. It is evident enough that the brain is not formed by the union of the nerves, and it is * These general sensations being founded on our knowledge of particular facts, we shall introduce them after having explained these facts. This course is conformable to the manner in which our ideas are formed. 116 FUNCTIONS of relation. equally certain that the nerves do not arise from the brain. By these expressions we merely mean to describe, metaphorically, the disposition of the two extremities of each nerve. [It was formerly supposed that the same nervous filament exe- cuted several different offices, as receiving impressions from with- out, transmitting them to the sensorium, communicating the man- dates of the will, and producing muscular motion. The unsound- ness of this doctrine has been established, especially by the in- vestigations of Sir Charles Bell. " No organ," says he, " which possesses only one endowment has more than one nerve, however exquisite the sense or action may be. But if two nerves are di- rected to one part, it is a sign of a double action performed by it. If a part or organ have many distinct nerves, we may be certain that, instead of having a mere accumulation of nervous power, it possesses several distinct powers, or enters into different combinations in proportion to the number of its nerves." The property imparted appears to depend upon the organiza- tion of the nerve, the part of the encephalon from which it is de- rived, and the structure of the part to which it is distributed. Thus the filaments which bestow voluntary motion are supposed by Sir C. Bell to be derived from the cerebrum; those which be- stow sensation, from the cerebellum. The greatest exactitude ap- pears to be indispensable in the distribution of the nerves. It is a matter of comparatively little importance what particular ar- terial branch conveys blood to a part, or what vein takes it away, as the circulating fluid is the same. Hence, great irregularity in the distribution of the bloodvessels, without its causing disturbance* of the functions, is often noticed. But assuming the facts stated above to be true, it is evident that the slightest deviation in the distribution of the nerves would be attended with serious incon- venience to the functions. A filament of motion, for example, can only bestow this property on a part so constituted as to pos- sess an aptitude for contraction, as muscular fibre, and would be unavailable if distributed to any other structure, &c. Hence, as was observed by Sir Charles Bell, if we make a minute dissection of the nerves of the face, for example, the innumerable branches exposed appear to run in all directions, like the arteries and veins, without regularity or order. But when carefully compared in a great number of subjects, taken from all the different varieties of the human species, we find that every ganglion, trunk, and twig presents with great exactitude the same arrangement.] The cerebral extremity of the nerves is composed of very fine and loose filaments, which are continued into the substance of the brain, for a short distance from the point where they are first per- ceived ; these filaments, when united, form the nerve. There is a marked difference between the nerves. Some are rounded, others flattened, others hollowed out at their sides, a great number are very long, and others very short. It may be asserted that, m form, colour, &c, there are no two nerves which exactly resemble each other. In general, they are so placed as SENSATIONS. 117 nbt to be exposed to injuries from external causes. In going to the different parts, the nerves divide into large, and afterward into smaller branches; and they terminate by filaments, so small, in the substance of the organs, that they cannot be distinguished, even by the assistance of the most powerful optical instruments. The nerves communicate among themselves, they anastomose, and thus form what is called a. plexus. With the exception of the optic nerve, the organic extremity of which can be easily distinguished, and of the auditory nerve, of which we have tolerably correct notions, we are absolutely ig- norant of the disposition of the extremities of the nervous filaments in the tissue of the organs. We hear much of the nervous ex- tremities, papilla, &.c Physiologists are still in the habit of using these expressions; but all that is said on this subject is purely imaginary. It is easy to demonstrate that those bodies which have been, and are still, called nervous papilla?, do not exist. The nerves are, in general, formed of filaments, excessively delicate, which are probably reducible into still finer filaments, if our means of division were more perfect. These filaments, which have been called nervous fibres, communicate frequently with each other, and effect, in the body of the nerve, an arrangement similar to what is found in a plexus. It is generally supposed that a fibre is formed by an envelope and a central pulp, similar in its nature to cerebral substance, but I believe that this is merely hy- pothetical. I have done all in my power to repeat the prepara- tions advised by anatomists to display this structure, but, with all my efforts, I have never been able to distinguish it. The tenuity of the nervous fibres alone appears to me to be a most powerful objection to it. Since with the aid of a microscope we can scarce- ly perceive the fibre itself, and may reasonably suppose that this is formed by fibres still more delicate, how, I would inquire, is it possible to distinguish a cavity filled with pulp ? Some years since, M. Bogross, a very expert anatomist, thought he had injected the nerves with mercury, by means of strong compression, but he had merely forced the injection under the neurilema, which included a great number of nervous fibrillae.* Whatever may be the disposition of the substance which forms the parenchyma of the nervous fibres, it is certain that it possess- es the same chemical properties as the cerebral substance, and that each nerve receives very numerous small branches of ar- teries, in proportion to its volume, and a proportionate number of small veins. The posterior branches of all those nerves which arise from the spinal marrow present, not far from the point where they unite with the anterior branch, an enlargement, which is called a gan- glion. These bodies are of a colour, consistence, and structure * I once saw, in the centre of the internal nerve of the penis of a horse, an appearance of a canal. Supposing that this appearance would be discoverable in other horses, I made every arrangement to attempt to inject it, but I never discovered it again. It was, no doubt, an accidental appearance. I 118 FUNCTIONS OF RELATION. essentially different from those of the nerves; their use is un- known. [They are of a rounded form, pinkish colour, of considerable density, in their general structure are very vascular, and some- what resemble the nerves. When cut, they have been thought to present an appearance like the gray substance of the brain. The only portion of the cerebro-spinal nerves in which they are found are what are called the regular nerves, viz., the spinal, including the fifth pair, or trigeminus, and the sub-occipital, which are more particularly destined to general sensibility. Numerous ganglia are also found attached to the great sympathetic nerve. The functions of these bodies are but little understood, and merit the particular attention of physiologists. Their study in living animals may lead to important discoveries connected with the of- fices of the nervous system. The following diagram exhibits a portion of nerve connected with a ganglion. G is the ganglion, N the nerve, which is seen to divide into nu- merous filaments at B and F. The next figure, A, is a representation, from Wagner, of the primitive fibres and ganglionic globules which form a ganglion of the great sympathetic, magnified 350 diameters. (Fig. 18.) From the investigations of Sir Charles Bell, it would appear, as has been already stated, that every nervous fibre, or elementary filament, runs directly from the central nervous mass, where it originates, to the muscle, organ of sense, or other part in which it terminates. What are called the trunks of the nerves, accord- ing to him, consist of fasciculi, or bundles, of these nervous fibres or elementary filaments, some of which are sensory and others motor. These fasciculi occasionally intermix and exchange fibres with each other, forming a plexus ; but the elementary fibres never SENSATIONS. 119 inosculate, each remaining distinct, and performing its appropri- ate office. The fasciculi are rolled up into trunks, and included in a common covering called the neurilema, merely for conveni- ence of distribution. The following figure will give an idea of those interlacings call- ed a plexus. Rmr nerves, T T, are divided into branches, which are variously separated and reunited. (Fig. 19.) Of the offices performed by the ganglia of the great sympa- thetic nerve little is known at the present day. The striking views taken of this subject by Bichat, that they were centres from which the great sympathetic nerve derived its nervous energy, and that its offices were executed to a great degree by the ganglia, independently of the encephalon, produced an influence upon the profession which is, even now, strongly felt. This is shown by the name given by him, ganglionic system of nerves, which, though ob- viously objectionable, from its seeming to indicate the great sym- pathetic as the only class of nerves which have ganglia, is still re- tained in common use. But when we examine the highest modern authorities, we find directly contradictory statements as to their utility and functions. Bichat states that he irritated the coeliac ganglion, both mechanically and by chemical stimuli, without ex- citing pain. Dupuy cut out the inferior ganglion of the neck and the first ganglion of the thorax without causing suffering to the animals; he also states that the wound closed up without being followed by an appreciable alteration of function in the parts to which filaments were distributed coming from these ganglia. The observations of Lobstein agree with the foregoing. On the con- trary, Flourens always observed, more or less, signs of pain. In Bracket's experiments there were sometimes manifestations of pain, and sometimes none. Mayer states that, both when the su- perior cervical ganglion was divided, and when the solar plexus was irritated, the animals gave distinct evidences of pain, which is also confirmed by Muller.* From these statements it appears that, in the present state of knowledge, it is very doubtful if the ganglia are concerned in the production of sensation, motion, and other properties which exist in those organs, the nerves of which are chiefly derived from the great sympathetic. But inasmuch as each of the compound nerves, on passing from the medulla spi- * See page 712, vol. i. 120 FUNCTIONS OF RELATION. nalis, directly communicates with the ganglia of the great sympa- thetic arranged along the sides of the vertebral column, it would seem probable that sensitive and motor filaments are sent off from these sources, and distributed with the filaments of the great sym- pathetic. According to this view, instead of supposing that the great sympathetic bestows several different properties, as sensa- tion, motion, nutrition, &c, we have the more probable supposi- tion that motion and sensation in these parts are derived from the cerebro-spinal system.*] Of the Mechanism, or Physiological Explanation of Sensations. The physiological explanation of sensations consists in the more or less exact application of the laws of physics and chemistry to the physical properties of that part of the organ which is placed before the nerves, as has been remarked in the particular history of each sensation. The moment we arrive at the use of the nerves in these functions, no farther explanation can be given. It is ne- cessary to adhere rigorously to facts. This consequence, so easy to deduce, does not seem to have been perceived but by a very small number of authors, and even in their works it is expressed very vaguely. All have endeav- oured to explain the action of the nerves. The ancients consider- ed these organs as the conductors of the animal spirits. At the period when physiology was governed by mechanical ideas, the nerves were supposed to be vibratory chords, although their phys- ical condition is such as to prevent their vibration. Some very intelligent men have supposed that the nerves were conductors, and even the secretory organs of a subtle fluid, which they have called nervous. According to them, sensations are transmitted to the brain by means of this fluid. At this moment, when the attention is directed towards the imponderable agents, this opinion has attracted numerous disciples. I am acquainted with men, who confer honour on the age by their genius and learning, who are inclined to admit that electricity exerts a con- siderable influence on the sensations and other functions. To * Why should we consider the great sympathetic as a nerve ? The ganglions and fila- ments which pass from it or lead to it have no analogy with the nerves, properly so called. Their colour, form, consistence, disposition, structure, and chemical properties are all dif- ferent ; nor have they any greater analogy in their vital properties. We may scratch or cut a ganglion, or even tear it, without the animal appearing to be conscious of it. I have often made these experiments on the ganglions in the necks of horses and dogs. Similar operations performed on a cerebral nerve will produce the most terrific pain. We may take away all the ganglions of the neck, and even the first ganglions of the thorax, with- out any sensible derangement in the functions even of those parts to which we can trace them. What reason is there, then, for considering the system of ganglions as constituting a part of the nervous system ? Would it not be more philosophical, and especially more useful to the future progress of physiology, to acknowledge that, at this moment, the uses of the great sympathetic are entirely unknown ? We shall be confirmed in this idea by reading on the subject. Every author has some peculiar opinions on this point. We hear, e. g., the ganglions considered as nervous centres, small brains, collections of cineritious substance for the nourishment of the nerves, &c. If we inquire after the proof by which these authors establish their doctrines, we are surprised not to find any, but that their as- sertions are mere freaks of the imagination. It appears to me that the functions of these singular organs, so intimately connected with the nerves, have not yet been discovered, but which may become unveiled to him who will take the trouble to mterrogate nature by delicate and ingenious experiments. SENSATIONS. 121 pretend to explain the sensations by referring them to certain vi- tal properties, which are called animal, perceptive, relative, &c, is to have recourse to a most vicious mode of explanation: it is only a new way of expressing the difficulty; it by no means solves it. We shall, therefore, class the action of the nerves among the vital actions, which, as has been seen at the commence- ment of this work, are not susceptible of explanation in the pres- ent state of science ; but that the nerves are the agents for the transmission of those impressions which are received from the senses, is conclusively demonstrated by observation and experi- ence. Thus, if a man receive a wound which affects a nervous trunk, the part to which the nerve is distributed becomes insensible. If the optic nerve be the one which has suffered, the individual will become blind; and if the auditory, deaf. We may produce these effects at any time upon brutes by dividing, or, even simply, by compressing the nerves. When the compression is removed, the nerve is restored to its sensibility as before. In man, as in brutes, the wounding of a nerve produces severe pain. In a word, all those diseases which alter, even slightly, the tissue of the nerves, have a manifest influence upon their action, as agents of sensa- tion. Science has recently made great progress, as respects the func- tions of the nerves: the views formerly entertained on this sub- ject have undergone an entire reform. The nerves are now dis- tinguished into sensible and insensible. The nerves of sensation are anatomically distinguishable by a ganglion situated near their origin. These nerves consist, 1st. Of the superior branch of the fifth pair, which imparts sensibility to the integument and mucous membranes of all the anterior part of the head. 2d. Of the nerves which result from the union of the posterior roots of the spinal nerves. They impart sensibility to the skin of the neck, trunk, ex- tremities, and almost all the organs of the breast and abdomen. 3d. Of the nerves of the eighth pair, which preside over the sen- sibility of the pharynx, oesophagus, larynx, and stomach. 4th. Of the sub-occipital, or tenth pair, which presides over the sensibility of the posterior part of the head, and a part of the external carti- lage of the ear. I have proved, by direct experiment, that if these different nerves are cut near their origin, the parts to which they are distributed lose their sensibility. The nerves that may be regarded as insensible (though this ex- pression does not absolutely hold true, inasmuch as among them are found the principal nerves of special sensation, those of seeing and hearing) are the optic, olfactory, and acoustic. But we have already seen that these three nerves have a special sensibility, which is, in great part, under the influence of the fifth pair. The knowledge of this influence of one nerve over the action of others is new in science, and is worthy the particular attention of physi- ologists. 122 FUNCTIONS OF RELATION. Many other nerves appear also to be destitute of sensibility; such are the third, fourth, and six pairs, the portio dura of the sev- enth, with the particular modifications above indicated; the hy- poglossal nerve, and the anterior branch of all the compound nerves which arise from the medulla spinalis. If these nerves be divided, the parts to which they are distributed still preserve their sensibility. In man, in a state of disease, when these nerves are alone interested, many functions are disturbed, but the faculty of sensation is not diminished. We are quite ignorant of the utility of the numerous anastomo- ses of the nerves; nor do we better understand the consequences which result from the communications between the nerves of sen- sation with the ganglions of the great sympathetic. The suppo- sitions that have been made to explain their use show sufficiently that, on this point, physiology is still in its infancy. Thus far, we have only spoken of the agents of sensation; let us next inquire respecting the phenomenon itself, describe its principal characters, and point out the most remarkable. Every sensation, at the moment when we experience it, is re- ferred to an external cause. We know that the impression per- ceived arises from something that is not a part of ourselves, or, as some would say, from the external world; so that to perceive an impression is at the same time to know, 1st. That it arises from some cause. 2d. That this cause is exterior to ourselves.* This surprising result is not the isolated work of the special organs of sensation; it is the first, as the most important, of the acts of the understanding, which I call instinctive, and, consequently, the prod- uct of the combined action of the brain and organs of the senses. To conjecture what takes place in the nervous system when we experience a sensation, transcends .the human understanding. Nevertheless, such is our irresistible disposition to form images wherever there is obscurity, that we imagine each sensation as resulting from the successive, but very rapid, development of a certain number of phenomena. Thus, in every sensation there is supposed to be the following acts: 1st. The action of the cause upon the sense. 2d. The action of the nerve to transmit it. 3d. The impression received by the cerebral centre. 4th. The in- stinctive reaction, which informs us that the cause of the sensation is exterior to us; often at a considerable distance, having as an intermediate agent air, light, or heat. Such is the image or idea that metaphysicians have formed of every complete sensation, to which some of our most learned ideologists have recently conse- crated the word perception. But is this very nice analysis, by which a sensation is divided into so many elements, real ? Is it possible to prove, physiologi- cally, these successive acts in an instantaneous phenomenon, and that the simplest known ? Does not the mind, impatient of doubt in proportion to our ignorance, impose upon itself this analytical * We here refer to sensations, properly so called, and not to internal sensations, which hereafter will be examined in this point of view. SENSATIONS. 123 romance, as in many other instances we mask our ignorance with the mere appearance of truth ? According to the experi- mental method that we hope always to pursue in these investiga- tions, the sensation, and, consequently, its relations with the exte- rior cause, are to us a singular phenomenon, the same and indi- visible as respects time or separate acts. It is not less possible that the nervous system perceives at its surface than its centre. The same instinct which induces us to place the cause of our sensations exterior to ourselves, leads us also to inquire, what is this cause, and what are its characters ? To arrive immediately at this knowledge constitutes one of our most urgent desires and most vivid pleasures. When, by a concurrence of circumstances, or from the nature of the cause of our sensation, it is impossible to recognise it, we feel anxiety, and make great efforts for this pur- pose ; and when we accomplish it, we experience great satisfac- tion. Sensations are either vivid or weak. The first time a body acts upon our senses, the impression produced is generally vivid. The vivacity of the impression diminishes, if the action of the body be frequently repeated, and, at last, it is scarcely perceived. This fact is expressed when we say that habit blunts our feelings. The existence of man being, as it were, measured out by the vivacity of his sensations, he is induced to seek continually for new im- pressions, which are always the most vivid ; hence his inconstan- cy, inquietude, and ennui, if he remain long exposed to the same causes of sensation. We possess the power of rendering our sensations more vivid and distinct. In order to do this, we dispose the organ of sense in the most favourable manner, we receive but a small number of sensations at a time, and we direct all our attention to them ; thus arises the important difference between seeing and examining, hearing and listening, the common exercise of the sense of smell, and snuffing, &c. Nature has also given us the power of dimin- ishing our sensations. Thus we draw down the eyebrows, and close the eyelids, when the impression produced by the light is too vivid ; we breathe through the mouth when we wish to dimin- ish the effect of a strong odour, &c. The different sensations also direct, assist, modify, and may even mislead each other. Smell seems to be the sentinel.and guide to taste, and taste, in its turn, exerts a powerful influence over smell. Smell may exercise its functions separately from those of taste, but the reverse cannot be always done, as the ali- ments and drinks cannot pass into the mouth without acting, more or less, upon the nose; whenever their taste is very disagreeable, their odour soon becomes so; again, those aliments, the odour of which is most unpleasant, soon loose this quality when the taste very vehemently desires them.* We know, from numerous observations, that the vivacity of the impressions received by the senses is increased by the loss of one * Cabanis. 124 FUNCTIONS OF RELATION. of these organs. For example, the smell is more delicate in blind or deaf persons than in those who enjoy all their senses. I think, however, that the absence of smell, which we often meet with, does not give any increased activity to the other senses. We have a curious history of a young man, born deaf and blind, who was observed by a number of scientific persons. James Mitchel was born the 11th of November, 1795, deaf and blind, but he experienced pleasure in rubbing hard bodies upon his teeth. He amused himself in this way, sometimes, for hours. He could distinguish day from night, and a few colours, red, white, and yellow. In his youth he amused himself by looking through the windows at the stin, and the light of the fire. His relations with surrounding bodies were principally established by smell and touch. At the age of fourteen years, M. Wardrop per- formed the operation of cataract on the right eye, which some- what improved his imperfect vision. After this, he had less fre- quently recourse to the sense of smell. He handled bodies in all directions with his head bent, as we observe in blind people. His desire to become acquainted with surrounding objects, as their quantities, uses, &c, was very vivid. He examined everything that came in his way, men, animals, and things ; his actions indi- cated reflection. One day, the shoemaker brought home a pair of shoes for him that were too small; his mother locked them up in a cabinet, and took the key. In a short time afterward, James asked his mother for the key by turning his hand. His mother gave it him, when, unlocking the cabinet and taking the shoes, he put them upon the feet of a little boy, who accompanied him in his excursions, and whom they fitted very well. During his infancy, he smelled all those who approached him, putting their hands to his nose, and snuffing the air. Their odour determined his liking or repugnance to them. He recognised his clothes by the smell, and was averse to use those of another; bodily exerci- ses amused him. His countenance was very expressive; his natural language that of an intelligent being. When he was hungry, he carried his hand to his mouth, and pointed to the closet where the food was kept. When he wished to lie down, he laid his head upon his hand. He imitated different employments, when he wished to in- dicate them, as the different motions of a shoemaker, a tailor, &c. He delighted in being placed on horseback, which he designated by joining his hands, and then placing them on the soles of his feet, to imitate a stirrup. He did not like to be embraced, and when his sister sometimes did so to amuse herself, he seemed annoyed by it. It was remarkable that all the signs he in- vented were intended for the sight of others. He appeared to know his inferiority in respect to this sense. He was usually ac- companied by a little boy in his excursions, and was allowed to fo wherever he chose ; if he met with any object that was un- nown to him, he waited until the arrival of his companion. He recognised readily the signs that were made to him. To make SENSATIONS. 125 him understand the number of days, they inclined his head upon his hand, as a sign that he would sleep so many nights before the event would happen. They testified their approbation by caress- ing him, their dissatisfaction by tapping him a little sharply. He was much gratified by the caresses of his parents; he loved young infants, and was fond of holding them in his arms. He was naturally kind and inoffensive, but his temper was not equal. Sometimes he was pleased to have persons play with him, and laughed heartily. One of his favourite amusements was to shut some one in a chamber, or in the stable. If he was opposed much, he uttered very disagreeable cries. He appeared general- ly contented. He possessed courage, naturally, but acted prudently. One day, he found in his way a narrow wooden bridge, which passed over a stream near his father's house. He got on his hands and knees to pass it. His father, in order to intimidate him, sent a man to push him into the water, at a place where there was no danger, and to take him out immediately. This lesson produced the desired effect; he never went to the bridge again. Some years afterward, he recollected this punishment. One day, his lit- tle companion having displeased, him while they were playing to- gether in a boat secured to the bank of the stream, he plunged him in, and then drew him out. [The following case, reported by Dr. Howe, of Boston, furnishes a number of still more striking physiological and psychological results. Laura Bridgman was born in New-Hampshire, December 21st, 1829. Her health was very infirm, being subject to fits until she was a year and a half old. After a temporary improvement, she was attacked by a severe disease, the consequence of which was destruction of the organs of hearing and vision, and confine- ment to her room, and chiefly to her bed, for nearly two years. As soon as her health was restored and she was enabled to walk about, she gave strong indications of intelligence and warm af- fections, though the means of communication with her were very limited. She could only be told to go to a place by being pushed, or to come to one by drawing her; patting her gently on the head indicated approbation; on the back, disapprobation. In October, 1837, then aged about eight years, she was brought to Boston and placed in the Perkins Institution for the Blind, under the care of its philanthropic director, Dr. Howe, to whom we are indebted for the interesting developments which mark this extraordinary case. For a time, she seemed bewildered, and it was thought prudent to wait for about two weeks, until she could become fa- miliarized with her kind teacher and friend, and her new locality, before making any systematic attempt to develop her faculties by education. " There were," says Dr. Howe," two ways to be adopted: either to build up a language of signs, on the basis of the natural lan- guage, which she had already commenced; or to teach her the 126 FUNCTIONS OF RELATION. purely arbitrary language in common use, i. e., to give her a knowledge of letters, by combination of which she might express her idea of the nature and mode of existence of anything. The former would have been easy, but very ineffectual; the latter seemed very difficult, but, if accomplished, very effectual. I de- termined, therefore, to try the latter." The results of this attempt have been furnished by Dr. Howe in the annual reports of the trustees of the Perkins Institution and Massachusetts Asylum for the Blind, from that time to the last annual report, 1842, from which the present account is extracted. The first experiments were taking articles in common use, as spoons, knives, keys, &c, and pasting upon them labels of their names in raised letters, as used for the blind. She soon learned to distinguish that the crooked lines upon the spoon differed from those upon the key. Then the labels were detached, and she showed her perception of their relation by placing the label key upon the key, and spoon upon the spoon. It was evident, however, that the only intellectual exercise was that of imitation and memory. At last, instead of labels, the individual letters, on detached pieces of paper, were given to her. They were arranged side by side so as to spell spoon, key, &c. They were mixed up, and she was desired, by a sign, to arrange them herself, which she did. Heretofore, says Dr. Howe, the process had been mechanical, and the success about as great as teaching a very docile dog a variety of tricks. The poor child had sat in mute amazement, and patiently imitated everything her teacher did; but now the truth began to flash upon her; her intellect began to work; she per- ceived that there was a way by which she could herself make up a sign of anything that was in her own mind, and communicate it to another mind. It was no longer the act of a dog or parrot, but that of a reasoning spirit, eagerly seizing upon a new link of union with other spirits of its kind. I could, says he, almost fix upon the moment when this truth dawned upon her and spread its light over her countenance. This, though briefly told, required many weeks of patient and persevering effort on the part of her kind teacher. From this moment, says he, I perceived that the great obstacle was overcome, and that henceforward nothing but plain and persevering exertion would be necessary. He next procured a set of metal types with the letters of the alphabet, and a board into which they might be conveniently set, and thus she could arrange the letters of the few words she knew and read them, which she appeared to do with great pleasure. After weeks of persevering instruction with this apparatus, until she had acquired an extensive vocabulary, this cumbrous arrange- ment was laid aside, and the manual alphabet of deaf mutes taught her in its place. This she accomplished speedily' and easily, for her intellect had begun to work in aid of her teacher, and her progress was very rapid. The manner of proceeding was thus. The teacher gave her a new object, e. g., a pencil; first, he let her examine it, and get an idea of its use. Then he SENSATIONS. 127 taught her how to spell it, by making the signs for the letters with her own fingers. " The child," says he," grasps her hand, and feels of her fingers, as the different letters are formed—she turns her head a little on one side, like a person listening closely—her lips are apart—she seems scarcely to breathe—and her countenance, at first anxious, gradually changes to a smile as she comprehends the lesson. She then holds up her tiny fingers and spells the word in the manual alphabet; next she takes her types and arranges the letters; and last, to make sure that she is right, she takes the whole of the types composing the word, and places them upon or in contact with the pencil or other object. " The whole of the succeeding year was passed in gratifying her eager inquiries for the names of every object which she could possibly handle ; in exercising her in the use of the manual alpha- bet; in extending, in.every possible way, her knowledge of the physical relations of things ; and in proper care of her health." At the end of the year, a report of her case was made, from which the following is an extract: " It has been ascertained, beyond the possibility of doubt, that she cannot see a ray of light, cannot hear the least sound, and never exercises her sense of smell, if she has any. Thus her mind dwells in darkness and stillness, as profound as that of a closed tomb at midnight. Of beautiful sights, and sweet sounds, and pleasant odours, she has no conception; nevertheless, she seems as happy and playful as a bird or a lamb ; and the employ- ment of her intellectual faculties, or acquirement of a new idea, gives her a vivid pleasure, which is plainly marked in her expres- sive features. She never seems to repine, but has all the buoy- ancy and gayety of childhood. She is fond of fun and frolic, and, when playing with the rest of the children, her shrill laugh sounds loudest of the group. " When left alone, she seems very happy if she has her knitting or sewing, and will busy herself for hours ; if she has no occupa- tion, she evidently amuses herself by imaginary dialogues, or by recalling past impressions; she counts with her fingers, or spells out names of things which she has recently learned in the manual alphabet of the deaf mutes. In this lonely self-communion, she seems to reason, reflect, and argue : if she spells a word wrong with the fingers of her right hand, she instantly strikes it with her left, as her teacher does, in sign of disapprobation; if right, then she pats herself upon the head, and looks pleased. She sometimes purposely spells a word wrong with the left hand, looks roguish for a moment and laughs, and then with the right hand strikes the left, as if to correct it. " During the year, she has attained great dexterity in the use of the manual alphabet of the deaf mutes, and she spells out the words and sentences which she knows so fast and so deftly, that only those accustomed to this language can follow with the eye the rapid motions of her fingers. " But wonderful as is the rapidity with which she writes her 128 FUNCTIONS OF RELATION. thoughts upon the air, still more so is the ease and accuracy with which she reads the words thus written by another, grasping their hands in hers, and following every movement of their fingers, as letter after letter conveys their meaning to her mind. It is in this way that she converses with her blind playmates ; and nothing can more forcibly show the power of mind in forcing matter to its purpose than a meeting between them; for, if great talent and skill are necessary for two pantomimes to paint their thoughts and feelings by the movements of the body and the expression of the countenance, how much greater the difficulty when darkness shrouds them both, and the one can hear no sound! "When Laura is walking through a passage-way, with her hands spread before her, she knows instantly every one she meets, and passes them with a sign of recognition ; but if it be a girl of her own age, and especially if one of her favourites, there is in- stantly a bright smile of recognition and a twining of arms, a grasping of hands and a swift telegraphing upon the tiny fingers, whose rapid evolutions convey the thoughts and feelings from the outposts of one mind to those of the other. There are questions and answers, exchanges of joy or sorrow; there are kissings and partings, just as between little children with all their senses. " During this year, and six months after she had left home, her mother came to visit her, and the scene of their meeting was an interesting one. " The mother stood some time gazing with overflowing eyes upon her unfortunate child, who, all unconscious of her presence, was playing about the room. Presently Laura ran against her, and at once began feeling of her hands, examining her dress, and trying to find out if she knew her; but, not succeeding in this, she turned away as from a stranger, and the poor woman could not conceal the pang she felt at finding that, her beloved child did not know her. " She then gave Laura a string of beads which she used to wear at home, which were recognised by the child at once, who, with much joy, put them around her neck, and sought me eagerly, to say she understood the string was from her home. " The mother now tried to caress her, but poor Laura repelled her, preferring to be with her acquaintances. " Another article from home was now given her, and she began to look much interested; she examined the stranger much closer, and gave me to understand that she knew she came from Han- over ; she even endured her caresses, but would leave her with indifference at the slightest signal. The distress of the mother was now painful to behold; for, although she had feared that she should not be recognised, the painful reality of being treated with cold indifference by a darling child was too much for woman's nature to bear. " After a while, on the mother taking hold of her again, a vague idea seemed to flit across Laura's mind that this could not be a stranger; she therefore felt of her hands very eagerly, while her SENSATIONS. 129 countenance assumed an expression of intense interest: she be- came very pale, and then suddenly red ; hope seemed struggling with doubt and anxiety, and never were contending emotions more strongly painted upon the human face. At this moment of painful uncertainty, the mother drew her close to her side and kissed her fondly, when at once the truth flashed upon the child, and all mistrust and anxiety disappeared from her face, as, with an expression of exceeding joy, she eagerly nestled to the bosom of her parent, and yielded herself to her fond embraces. " After this the beads were all unheeded ; the playthings which were offered to her were utterly disregarded; her playmates, for whom, but a moment before, she gladly left the stranger, now vainly strove to pull her from her mother; and though she yield- ed her usual instantaneous obedience to my signal to follow me, it was evidently with painful reluctance. She clung close to me, as if bewildered and fearful; and when, after a moment, I took her to her mother, she sprang to her arms and clung to her with eager joy. "Having acquired the use of substantives, adjectives, verbs, prepositions, and conjunctions, it was thought time to make the experiment of trying to teach her to write, and to show her that she might communicate her ideas to persons not in contact with her. " It was amusing to witness the mute amazement with which she submitted to the process, the docility with which she imitated every motion, and the perseverance with which she moved her pencil over and over again in the same track, until she could form the letter. But when at last the idea dawned upon her that, by this mysterious process, she,could make other people understand what she thought, her joy was boundless. " Never did a child apply more eagerly and joyfully to any task than she did to this; and in a few months she could make every letter distinctly, and separate words from each other; and she actually wrote, unaided, a legible letter to her mother, in which she expressed the idea of her being well, and of her expect- ation of going home in a few weeks. It was, indeed, a very rude and imperfect letter, couched in the language which a prattling infant would use ; still it shadowed forth, and expressed to her mother, the ideas that were passing in her own mind. " She is familiar with the processes of addition and subtraction in small numbers. Subtraction of one number from another puz- zled her for a time, but by the help of objects she accomplished it. She can count and conceive objects to about one hundred in number; to express an indefinitely great number, or more than she can count, she says hundred. If she thought a friend was to be absent many years, she would say will come hundred Sundays, meaning weeks. She is pretty accurate in measuring time, and seems to have an intuitive tendency to do it. Unaided by the changes of night and day, by the light, or the sound of any time- piece, she nevertheless divides time pretty accurately. 130 FUNCTIONS OF RELATION. " With the days of the week, and the week itself as a whole, she is perfectly familiar: for instance, if asked what day will it be in fifteen days more, she readily names the day of the week. The day she divides by the commencement and end of school, by the recesses, and by the arrival of meal times. " Those persons who hold that the capacity of perceiving and measuring the lapse of time is an innate and distinct faculty of the mind, may deem it an important fact that Laura evidently can measure time so accurately as to distinguish between a half and whole note of music. " Her judgment of distances and of relations of place is very accurate. She will rise from her seat, go straight towards a door, put out her hand just at the right time, and grasp the handle with precision." These extracts from former reports bring down the history of her instruction to the commencement of the year 1840, when she had been two years and two months under instruction. In the next Annual Report, for 1841, she is stated to be eleven years of age, in good health. There was still no indication of her perceiving light or sound, with, perhaps, some slight but not es- sential improvement in the sense of smell. The touch had evi- dently improved in acuteness. " Her mental perceptions, resulting from sensation, are much more rapid than they were, for she now perceives, by the slight- est touch, qualities and conditions of things similar to those she had formerly to feel long and carefully for. So with persons: she recognises her acquaintances in an instant, by touching their hands or their dress ; and there are probably fifty individuals who, if they should stand in a row, and hold out each a hand to her, would be recognised by that alone. " The memory of these sensations is very vivid, and she will readily recognise a person whom she has once thus touched. Many cases of this kind have been noticed ; such as a person sha- king hands with her, and making a peculiar pressure with one finger, and repeating this on his second visit, after a lapse of many months, being instantly known by her. She has been known to recognise persons whom she had thus simply shaken hands with but once, after a lapse of six months. " The moral qualities of her nature have also developed them- selves more clearly. She is remarkably correct in her deport- ment, and few children of her age evince so much sense of pro- priety in regard to appearance. Never, by any possibility, is she seen out of her room with her dress disordered; and if. by chance, any spot of dirt is pointed out to her on her person, or any little rent in her dress, she discovers a sense of shame, and hastens to remove it. " She is never discovered in an attitude or an action at which the most fastidious would revolt, but is remarkable for neatness, order, and propriety. " There is one fact which is hard to explain in any way; it is SENSATIONS. 131 the difference of her deportment to persons of different sex. This was observable when she was only seven years old. She is very affectionate, and when with her friends of her own sex she is con- stantly clinging to them, and often kissing and caressing them; and when she meets with strange ladies she very soon becomes familiar, examines very freely their dress, and readily allows them to caress her ; but with those of the other sex, it is entirely differ- ent, and she repels every approach to familiarity. She is attach- ed, indeed, to some, and is fond of being with them; but she will not sit upon their knee, for instance, or allow them to take her around the waist, or submit to those innocent familiarities, which it is common to take with children of her. age. " She seems to have also a remarkable degree of conscientious- ness, for one of her age ; she respects the rights of others, and will insist upon her own. " She is fond of acquiring property, and seems to have an idea of ownership of things which she has long since laid aside and no longer uses. She has never been known to take anything belong- ing to another, and never, but in one or two instances, to tell a falsehood, and then only under strong temptation. " It has been remarked, in former reports, that she can distin- guish different degrees of intellect in others, and that she soon re- garded, almost with contempt, a new-comer, when, after a few days, she discovered her weakness of mind. This unamiable part of her character has been more strongly developed during the past year. " She chooses for her friends and companions those children who are intelligent, and can talk best with her; and she evident- ly dislikes to be with those who are deficient in intellect, unless, indeed, she can make them serve her purposes, which she is evi- dently inclined to do. She takes advantage of them, and makes them wait upon her, in a manner that she knows she could not exact of others, and, in various ways, she shows her Saxon blood. " She is fond of having other children noticed and caressed by the teachers and those whom she respects; but this must not be carried too far, or she becomes jealous. She wants to have her share, which, if not the lion's, is the greater part; and if she does not get it, she says,' My mother will love me.' " Her tendency to imitation is so strong, that it leads her to ac- tions which must be entirely incomprehensible to her, and which can give her no other pleasure than the gratification of an internal faculty. She has been known to sit for half an hour, holding a book before her sightless eyes, and moving her lips, as she has ob- served seeing people do, when reading. " She one day pretended that her doll was sick, and went through all the motions of tending it and giving it medicine; sfre then put it carefully to bed, and placed a bottle of hot water to its feet, laughing all the time most heartily. When I came home, she insisted upon my going to see it and feel its pulse ; and when I 132 FUNCTIONS OF RELATION. told her to put a blister to its back, she seemed to enjoy it ama- zinglv, and almost screamed with delight. " Her social feelings and her affections are very strong; and when she is sitting at work, or at her studies, by the side of one of her little friends, she will break off from her task every few moments to hug and kiss them, with an earnestness and warmth that is touching to behold. " When left alone, she occupies, and apparently amuses herself, and seems quite contented ; and so strong seems to be the natural tendency of thought to put on the garb of language, that she often soliloquizes in the finger language, slow and tedious as it is. But it is only when alone that she is quiet, for if she becomes sensible of the presence of any one near her, she is restless until she can sit close beside them, hold their hand, and converse with them by signs. " She does not cry from vexation and disappointment, like other children, but only from grief. If she receives a blow by accident, or hurts herself, she laughs and jumps about, as if trying to drown the pain by muscular action. If the pain is severe, she does not go to her teachers or companions for sympathy, but, on the con- trary, tries to get away by herself, and then seems to give vent to a feeling of spite, by throwing herself about violently and roughly handling whatever she gets hold of. " Twice only have tears been drawn from her by the severity of pain, and then she ran away, as if ashamed of crying for an accidental injury; but the fountain pf her tears is by no means dried up, as is seen when her companions are in pain or her teacher is grieved. " In her intellectual character, it is pleasing to observe an in- satiable thirst for knowledge, and a quick perception of the rela- tions of things. In her moral character, it is beautiful to behold her continual gladness, her keen enjoyment of existence, her ex- pansive love, her unhesitating confidence, her sympathy with suf- fering, her conscientiousness, truthfulness, and hopefulness." Her ideas of death are interesting. It appears that, before be- ing brought to the institution, she had been taken to a funeral, and touched a dead body. " She was acquainted with two little girls, sisters, in Cambridge, Adeline and Elizabeth. Adeline died during the year before last. Not long since, in giving her a lesson in geography, her teacher began to describe Cambridge; the mention of Cambridge called up a new subject, and she asked, ' Did you see Adeline in box V I answered, Yes. ' She was very cold, and not smooth; ground made her rough.' I tried to change the subject here, but it was in vain; she wished to know how long the box was, &c.; she said, ' Drew told me about Adeline; did she feel ? did Elizabeth cry and feel sick ? I did not cry, because I did not think much about it! She then drew in her hands shudderingly, as if cold. I asked her what was the matter. She said, ' J thought about (how) / was afraid to feel of dead man before I came here, when I § SENSATIONS. 133 was very little girl with my mother; I felt of dead heads eyes and nose; I thought it was man's; I did not know.' Now, it is im- possible that any one could have said anything to her on the sub- ject ; she could not know whether the state the man was in was temporary or lasting ; she knew only that there was a human be- ing, once moving and breathing like herself, but now confined in a coffin, cold, and still, and stiff, in a state which she could not comprehend, but which nature made her recoil from. " During the past year, she all at once refused to eat meat, and being asked why, she said,' Because it is dead.' I pushed the in- quiry, and found she had been in the kitchen and felt of a dead turkey, from which she suddenly recoiled. She continued disin- clined to eat flesh for some weeks, but gradually she came to her appetite again; and now, although she understands that fowls, sheep, calves, &c, are killed to furnish meat, she eats it with relish." We may conclude from these cases, though vision and hearing furnish many facts to the understanding, still that it may attain considerable development without their aid. There is another singular and unexpected result lately observ- ed. In ordinary circumstances, at the period of birth, the senses act with little skill; they are gradually developed by exercise, and at the age of a year, the infant has nearly the complete en- joyment of all his senses. But it sometimes happens that certain physical causes prevent the development of one of the senses, and this most frequently occurs to hearing. If these causes are of a nature to remain long, the individual loses all idea of sound, as in deaf mutes from birth. It has been long supposed that, if the obstacle to hearing in such cases could be removed, the individu- al would be situated like a new-born child, and that the hearing would become gradually developed by use as in other persons, and that if he had attained an age that rendered him capable of reflection, that the acquisition of a new sense would be mpst high- ly appreciated by him. But this does not appear to be the ease. Several instances have been recently observed where deaf mutes have been restored to hearing at from ten to fifteen years of age. But they seemed to attach but little value to the new sense, and were not inclined to make much use of it. They were still dis- posed to continue to communicate by gestures, and to pay but lit- tle attention to sounds. In order that one deaf from birth may derive much advantage from hearing, a long and laborious course of education is indispensable, and still such individuals never use their hearing like one with all their senses perfect from birth.] Sensations are agreeable or disagreeable; the first, when they are vivid, constitute pleasure, and the second pain. By pleasure and pain nature induces us to concur in the order which she has established among organized beings. Though it may appear like sophistry to say that pain is but the shadow of pleasure, still it is certain that persons who have ex- 134 FUNCTIONS OF RELATION. hausted all the sources of pleasure, and have thus become insen- sible to all ordinary sensations, have recourse to the causes of pain, and gratify themselves by their effects. Do we not see, in all large cities, that men who are debauched and degraded, find agreeable sensations where others experience nothing but the most intolerable pain ? It is necessary to remark, that those sensations which come from the senses are distinct. All our ideas, and the knowledge we have of nature, are thus received. Internal sensations, or sen- timents, do not possess these characters. In general, they are confused, and often vague; we are not conscious of them; they are not engraved upon the memory, but are always more or less fugitive, especially when in health. Whenever our organs act freely, and according to the ordinary laws of organization, our thoughts are agreeable, the pleasure is sometimes very vivid. But when the functions are deranged, the organs wounded, or diseases have impaired their action, our in- ternal sensations are painful, according to the nature of the injury. There is sometimes a degree of vivacity in these internal sen- sations which absorbs all our attention, so that we scarcely notice our external sensations. Those internal sensations arising from disorder of the functions are extremely varied, and generally dif- ferent from those of health. We experience, as in external sen- sations, an instinctive disposition to refer them to some cause, and that cause has a place. But we often deceive ourselves, in be- lieving the seat of the sensation to be in one part when it is really in another. In this respect, there are some illusions so uniform, that they are signs of a certain disease. Thus, in diseases of the hip joint, the pain is frequently altogether in the knee ; a stone in the bladder causes pain about the glans penis. Thus pain and other sensations which accompany diseases become objects of great interest, in the studies of the physician.* It is probable that the nerves which pass directly from the brain or spinal marrow are the organs for the transmission of in- ternal sensations. The physiologists of the present day, however, appear to attribute this function to the nerve which is called the great sympathetic. We cannot say positively that it is not so, but it is impossible to admit this doctrine, as it is not founded on any fact or direct experiment. The causes which modify internal and external sensations are innumerable. Age, sex, temperament, seasons, climate, habit, and individual character, each separately modify sensation ; but when they are united, the result is much more manifest. The differ- ence of sensations among different individuals is expressed by the common maxim, " Every one has his own way of feeling and thinking." * After certain surgical operations, some strange illusions become developed. An am- putated limb will seem to suffer. When the skin has been removed from the forehead to form an artificial nose, various sensations are observed, which are referred to the part from which the integument was taken. THE ENCEPHALON. 135 It is probable that only internal sensations exist in the foetus. We are led to suppose this by the motions which it executes, which appear to be the result of impressions arising spontaneously in the organs. It is well known, from experiment, that when any derangement arises in the circulation or respiration of the mother* it is followed by the motions of the foetus. All the senses are not found to exist at birth, or for some time afterward. Taste, touch, and smell are alone exercised; sight and hearing are developed later, as we have observed in the history of each particular func- tion. Each sense must pass through different degrees before it can arrive at perfection; it is^ indispensable, therefore, that each sense should receive what may properly be called an education. If any person will follow an infant in the development of its sen- ses, he may easily satisfy himself of the modifications they under- go before arriving at perfection. In those sensations which are produced by distant objects, the education is slow and difficult; in those which arise from con- tact, it is much more prompt, and appears to be easily effected. During this education of the senses, that is, in our infancy, the sensations are confused and weak; but afterward, especially those of young people, they are remarkable for their number and vivacity. At this age, they are deeply engraved in the memory, and, of consequence, are destined to constitute a part of our intel- lectual existence during the remainder of our lives. With the progress of age, our sensations lose their vivacity, but become more perfect, as respects exactness, after arriving at the adult age. In old age, they grow weak, and are produced with slow- ness and difficulty. This effect is more remarkable in those sen- ses which make us acquainted with the physical properties of bodies, but much less so in those by which we become informed of their chemical properties. These last senses, those of taste and smell,- alone preserve any activity in decrepitude; the others are nearly extinguished by the diminished sensibility and the succes- sive physical alterations which they undergo. CHAPTER IX. OF THE FUNCTIONS OF THE ENCEPHALON. The most sublime features in the human character are in- telligence, thought, the passions, and that admirable faculty by which we are enabled to direct our movements, and commu- nicate by speech. These phenomena are dependant upon the brain, and are designated by many physiologists as the cerebral functions. Other physiologists, sustained and inspired by re- ligious creeds, regard them as belonging to the soul, a being de- 136 FUNCTIONS OF RELATION. rived from the Divine essence, of which immortality is one of the attributes. It would not be becoming in us to undertake to de- cide here between these two modes of contemplating this impor- tant subject; our object is science, not theology. Besides, we do not pretend to explain the acts of the understanding or the in- stincts ; our object is to study them, and to demonstrate the physi- ological connexion they may have with the brain generally, or with certain of its parts. We shall observe this method of study- ing the phenomena of the understanding, and thus endeavour to avoid some of the errors into which those have fallen who have pursued a different course. Under the denomination of encephalon I include three parts, distinct from each other, though they are all united at certain points ; they are the cerebrum, cerebellum, and medulla spinalis. In each of these principal divisions we find distinct parts which have a sort of separate existence, so that there is nothing more complicated and difficult in anatomy than the study of the organization of the encephalon. In proportion, however, to the importance of the function of this organ, anatomists and philoso- phers have at all times devoted themselves to its dissection. The result of this is, that the anatomical history of the brain is one of the most perfect parts of anatomy. Very lately, this subject has been much elucidated by the publication of many new works, which have introduced some important improvements in this interesting part of the science. The encephalon being of an extremely delicate texture, and its function being easily destroyed by the least derangement, nature has taken uncommon care to protect it from injuries arising from the contact of surrounding bodies. Among the protecting parts of the brain, which have received the denomination tutamina cerebri, we remark the hair, the scalp, the muscles, the pericranium, the bones of the scull, and the dura mater, which are particularly destined to guard the cerebrum and cerebellum. By its quantity and arrangement, the hair is very suitable to weaken the effects of blows upon the head. As it is a bad con- ductor of caloric, it forms a covering, the texture of which being loose, intercepts a large number of small masses of air; it is well disposed, therefore, to preserve the head of a uniform tempera- ture, in some sort, independently of the air or surrounding bodies. As it is impregnated with an oily substance, it imbibes but a small quantity of water, and dries rapidly. The hair being also a bad conductor of the electric fluid, it in some degree insulates the head; hence the head is less likely to be affected by this agent. It is easy to conceive how the scalp, the muscles which cover the cranium, and the pericranium, concur in protecting the brain; it will not be necessary, therefore, to insist on this point. But of all the means of protecting the encephalon, the most effi- cient is the collection of bones, called the cranium, which com- pletely envelop this organ. In consequence of the hardness and ENCEPHALON. 137 strength of this envelope, and its spherical form, all pressure or percussion exerted upon any given part of the head is distributed from this point to all the rest, and is, therefore, less felt by the brain. If, for example, a man receives a blow from a cane on the top of his head, the motion will be propagated in every direc- tion, and will extend even to the middle part of the base of the cranium, that is, even to the body of the sphenoid bone; if the blow be given upon the forehead, the motion will be propagated towards the middle of the occipital bone. In this transmission of motion through the bones of the cranium, it has been supposed that these bones experienced a slight, but reciprocal displacement, which were with difficulty distinguished, in consequence of the disposition of the different articulations. There are, however, good reasons to believe that the cranium resists as if it were a single bone. Authors have not dwelt sufficiently upon the fact, that it must necessarily happen, that the cranium will change its form when- ever it is pressed, or struck smartly. The softness of the cerebral mass will enable it to endure slight changes in the form of its en- velope without any serious injury. The softer the brain is, the more able it will be to suffer strong pressure, or percussion, with- out inconvenience. This is the reason why newborn infants, in whom the bones of the cranium are very movable upon each other, often have the head strongly compressed, and even sensibly deformed, without any injurious consequences. The same things exist, in a degree, in children at a more advanced age, who receive, without danger, violent blows upon the head. In the early periods of life, the brain is much softer than in the adult.* The dura mater is so arranged as to protect the brain, as it were, against itself. Indeed, without the folds which are formed by this membrane, viz., the falciform process and the tentorium, one hemisphere of the cerebrum would press upon the other when the head was inclined to one side, and the brain would compress the cerebellum when the head was erect; so that the different parts of the organ would destroy each other. [The figure on the following page represents a longitudinal sec- tion of the head by Magendie; in which we see the encephalon, palate, tongue, falx, and pituitary membrane that lines the nasal passages. 1,1,1,1. Longitudinal section of the cranium. 2,3. Section of the superior and inferior maxillary bones. 4. Epiglottis. 5, 5. Section of the vertebral column. 6. Sphenoidal sinus. 7. Front- al sinus. 8. The septum narium lined with the pituitary mem- brane. 9. The internal orifice of the Eustachian tube. 10. A section of the veil of the palate and uvula. 11. The amygdalae or tonsils. 12. Portion of the pharynx. 13. The palatine arch. 14. Section of the tongue. 15. Genio-glossus muscle. 16. Genio-hy- * If the brain were perfectly fluid and homogeneous, whatever might be the changes in the form of its envelope, there would not result any injurious effects. But, as the brain is of a soft consistence, and not homogeneous, it follows that violent blows are often followed by serious consequences, such as concussion, extravasation of blood, abscess, &c. 138 FUNCTIONS OF RELATION. (Fig. 20.) oideal muscle. 17. Falx cerebri. 18,18,18. Superior longitudi- nal sinus. 19. Inferior longitudinal sinus. 20. Right sinus. 21. The vein of Galen divided. 22. Confluence of the sinuses, opened. 23. Falx cerebelli. 24, 24. Internal face of the right hemisphere of the cerebrum. 25, 25. Section of the corpus callosum. 26. Right lateral ventricle. 27. Right thalamus nervi optici. 28. Tuberculae quadrigeminae. 29. Pineal gland. 30. Section of the peduncles of the brain. 31. Section of the cerebellum, arbor- vitae. 32. Section of the peduncles of the cerebellum. 33. Sec- tion of the cerebral protuberance, or pons varolii. 34. Section of the medulla spinalis. 35. Right anterior cerebral artery. 36. The vertebral artery of the same side. 37. Naso-palatine nerve. 38. Internal branches of the left olfactory nerve. 39,39. Branches of the spheno-palatine artery distributed to the septum and pitui- tary membrane. The following figure represents the base of the encephalon de- prived of its membranes and the encephalic nerves. 1,1. Anterior lobes. 2. Middle lobes. 3. Posterior lobes; they constitute the base of the cerebral hemispheres, 9, 9, 9. 4. Fissure of Silvius. 5. Tuber cinnereum. 6. Infundibulum. 7,7. Mammillary tubercles. 8.8. Anterior peduncles of the cerebrum. 10,10,10. Circumference of the inferior surface of the hemispheres of the cerebellum. 12, 12. Anterior lobes of the cerebellum. 13, 13. Lobules of the medulla oblongata. 14. Lobules of the nervus vagus. 15,15. Lobules of the medulla oblongata. 16,16. THE ENCEPHALON. 139 (Fig. 21.) Peduncles of the cerebellum. 17. Pons varolii. 18. Medulla spinalis. 19,19. Pyramidal eminences. 20,20. Corpora olivaria. 21,21. Olfactory nerves. 22,22. Bulbs of these nerves. 23,23. Roots of these nerves. 24, 24. Optic nerves. 25. Junction of the optic nerves. 26,26. Common occular motor nerves. 27, 27. Pathetic nerves. 28, 28. Trigemini nerves. 29, 29. External occulor motor nerves. 30, 30. Facial nerves. 31, 31. Acoustic nerves. 32, 32. Glosso-pharyngeal nerves. 33, 33. Pneumo-gas- tric nerves. 34, 34. Hypo-glossal nerves. 35, 36. Vertebral nerves. 37. Section of the medulla spinalis.] If we compare the precautions taken by nature to preserve the cerebrum and cerebellum from external injury, with those which we find she has guarded the spinal marrow, we shall be led to in- fer that this last is even of greater importance than the first; or that its texture, being more delicate, requires extreme care. This is, in fact, the case. The spinal marrow holds a rank in the animal economy at least as important as the cephalic portion of the ner- vous system. The least shock wounds it, the least compression destroys its functions in a moment. It was therefore necessary that the vertebral canal, which contains it, should afford a power- ful protection. This end is attained in a manner so perfect, that 140 FUNCTIONS OF RELATION. nothing is more rare than an injury of the spinal marrow. The vertebral column necessarily unites great solidity with great mo- bility. It is the centre of motion in all the efforts of the body; it is also the centre of motion in the action of the extremities, and executes very extensive movements itself. We cannot here enter into the details of this admirable mecha- nism. We refer the reader to the " Anatomie Descriptive de Bichat," for a* farther account of this subject. But I have recently discovered an arrangement unknown to Bichat, which contributes powerfully to preserve the integrity of the spine. The canal formed by the dura mater around the medulla spi- nalis, and which is lined by the arachnoid, is much larger than is necessary to contain this organ. Thus, in the dead body there is an empty space between the medulla and its membranous enve- lopes. I have named this space the sub-arachnoidean cavity. But during life, this space is filled by a serous fluid which distends the membrane, and which is projected several inches when a small puncture is made in the dura mater. There exists an anal- ogous arrangement about the cerebrum and cerebellum, which do not fill exactly the cranium. I have given to this fluid the name cephalo-rachidian, or cephalo-spinal. It is not difficult to perceive that this fluid, which surrounds, and, as it were, suspends the medulla spinalis, somewhat like the foetus in utero, must afford this organ efficient protection. Besides the different envelopes of the brain, of which we have spoken, and the dura mater, which encloses it in its whole extent, this organ is surrounded by a very delicate serous membrane, which is called the arachnoides, the principal use of which is to form a very thin fluid, which lubricates the brain. The arach- noides penetrates into all the cavities of the brain, and forms there a perspiratory fluid. The manner that the bloodvessels enter and pass out from the brain is extremely curious. We shall enter more particularly into a consideration of this subject when we come to treat of the circulation. We shall only remark here, that the arteries, before penetrating into the substance of this organ, are reduced to capil- lary vessels, and that the veins affect the same disposition in pass- ing out from this substance. As these very fine blood-vessels communicate with each other by numerous anastomoses, the re- sult is, that there is formed on the surface of the brain a vascular network, *which has, very improperly, been called the pia mater. This network is introduced into the cavities of the brain, and it is this which forms the plexus choroides. We shall not pretend to give here a description of the anatomy of the brain, but shall limit ourselves to some general reflections on the subject. Almost all authors, who have given an anatomi- cal description of the brain in their works, have neglected to observe a proper strictness in the expressions employed, and have suffered their minds to be influenced by preconceived and THE ENCEPHALON. 141 hypothetical opinions. It is indispensable for the future prog- ress of anatomy and physiology, that we should employ terms which are precise, to avoid, as much as possible, hypothetical ex- pressions, and, above all, to reject the supposition that the nerves terminate or unite at any given point of the brain; that the soul has its seat in any particular part of this organ; or that the ner- vous fluid is secreted by a certain portion of the cerebral mass, while the rest serves as a conductor of this fluid, &c. From neg- lecting this method, those authors who have described the brain have presented false ideas, expressed in an obscure manner. When we speak of the encephalon, we mean the organ that fills the cavity of the cranium, and the vertebral canal. To facilitate the study of it, anatomists have divided it into three parts, viz., the cerebrum, the cerebellum, and medulla spinalis. This, how- ever, is purely a scholastic distinction; in fact, these three parts form but one organ. The spinal marrow is no more a prolonga- tion of the cerebrum and cerebellum than these are an expansion of the spinal marrow. The brain in man presents great complications of structure and numerous distinct parts, which are not found in any other animal, as the corpora mammillaria and olivaria. Others are seen in many animals, but we are ignorant of their uses; as, the corpus callo- sum, septum lucidum, cornu ammonis, the anterior and posterior commissure, the pineal gland, the pituitary gland, and the infun- dibulum. All these parts no doubt execute important functions, but so defective has been the method of studying the cerebral functions that we are quite ignorant of them. There are some other parts of the brain the uses of which are beginning to be un- veiled by experiment; the corpora striata, the thalami nervorum optioorum, the tubercula quadrigemina, the pons varolii, the py- ramidalia and their prolongation beyond the corpora striata, the peduncles of the cerebellum, the hemispheres of these organs, and the different fasciculi which form the medulla oblongata and medulla spinalis. In man, the encephalon is more voluminous than in other ani- mals. The dimensions of this organ are proportioned to those of the head. Individuals differ very much in this respect. Gener- ally speaking, the volume of the brain is in a direct proportion to the capacity of the mind. It would be incorrect, however, to suppose that every man who has a large head must necessarily be possessed of a superior intellect, because many causes, besides the volume of the brain, may increase the size of the head. But it is, nevertheless, very rare that a man distinguished for his men- tal faculties is not found to have a large head. The only means of ascertaining the volume of the brain in man, during life, is to measure the dimensions of the cranium. No other method, not even that proposed by Camper, can be relied upon. The cerebrum of man presents more numerous circumvolu- tions, and deeper inequalities, than other animals. The number, volume, and arrangement of the circumvolutions are various. In 142 FUNCTIONS OF RELATION. some brains, they are very large, and in others they are numerous and small. Their disposition differs in each individual. Those of the right side are not arranged like those of the left. It would be an interesting point to determine whether there exists any re- lation between the number of the circumvolutions and the per- fection or imperfection of the intellectual faculties; between the modifications of the mind, and the disposition of the individual, and the arrangement of the cerebral circumvolutions. The hemispheres of the human brain are distinguished by a posterior lobe, which covers the cerebellum. The general form of the lobes of the brain vary in individuals, and perhaps also according to the intellectual capacity. In the brain of one of the most learned and illustrious individuals who have honoured France, they were nearly hemispherical. The volume and weight of the cerebellum differ in different in- dividuals, and at different periods of life. In the adult, the cere- bellum is equal to the eighth or ninth part of the cerebrum; but it forms only the sixteenth or eighteenth part in newborn infants. We do not find circumvolutions on the surface of the cerebellum, but it is divided into lamellae, each being separated by a furrow. The number and arrangement of these lamellae differ in different individuals. We may here repeat the observation which was made above, in speaking of the cerebral circumvolutions. An Italian anatomist, Malacarne, is said to have found but three hun- dred and twenty-four of these lamellae in the cerebellum of an idiot, while, in other individuals, he found more than eight hun- dred. I have opened the heads of a great number of persons la- bouring under mental afienation of various kinds, but without the same result. In the depth of the cerebral substance, there are cavities which, from a remote period have been known by the name of ventri- cles. Of these cavities, one belongs to the cerebellum and me- dulla spinalis, and is the fourth ventricle; another is situated between the cerebral lobes, and is the third ventricle; lastly, in each of the hemispheres there is a much more spacious cavity than the preceding; these are the lateral ventricles. These differ- ent cavities communicate freely together; the third ventricle with the lateral ventricles by means of the two rounded openings called the holes of Monroe. A canal, known as the aqueduct of Silvius, unites the third and fourth ventricles. Lastly, the fourth ventricle communicates by an opening discovered by me some years since, which, variable in its extent and configuration, is al- ways placed over the median line opposite to the calamus scrip- torius, and opens into the sub-arachnoidean cavity, and is, conse- quently, immediately connected with the cephalo-rachidian fluid. By this opening, this fluid penetrates into the cavities of the brain, and, in certain cases, accumulates in considerable quantities. The mechanism by which the fluid enters into the ventricles and passes out by this opening will be described in its place. The substance of the cerebrum is soft and pulpy; its form is THE ENCEPHALON. 143 easily altered; in the foetus, it is almost fluid; it has more con- sistence in childhood, and still more in the adult. We find, also, that the degree of consistence varies at different points of the or- gan, and in different individuals; the odour is insipid, and resem- bles that of the semen, and remains for many years in dried brains. We find two substances in the brain. The one is gray and the other white. The first is called the cineritious, and the other the medullary substance. The medullary portion constitutes the greater part of the organ; it occupies more particularly the inte- rior of it, and that part which corresponds to the base of the cra- nium. It has a fibrous appearance, and possesses more firmness than the cineritious part; and it forms a great part of the spinal marrow, particularly near its surface. The cineritious substance, which is sometimes called cortical, forms a lamina varying in thickness on the external part of the cerebrum and cerebellum; and is likewise found in some of the internal parts. In some parts, it is covered by medullary matter, in others it seems intimately combined with it, and sometimes these two substances are disposed in laminae or alternate striae. We find other parts in the brain distinguished by their colour, viz., yellow, black, &c* To say that the cineritious substance of the brain produces the white part is entirely gratuitous. Indeed, the cineritious no more produces the white part of the brain than a muscle produces the tendon in which it terminates, or the heart the aorta. In this re- spect, the anatomical system of Messrs. Gall and Spurzheim is un- founded. Besides, generally, the white matter is formed before the gray, and many white parts have no connexion with the gray. When we examine the cerebral substance by means of a mi- croscope, it appears to be formed of an immense number of glob- ules, of unequal magnitude ; they are said to be about eight times smaller than those of the blood. In the medullary substance, they are disposed in right lines, and have the appearance of fibres; in the cineritious substance, they seem to be thrpwn confusedly together. According to M. Vauquelin, there is no difference in the chem- ical composition of the different parts of the nervous system. The analysis of the cerebrum, cerebellum, spinal marrow, and nerves, exhibit the same results. He found them composed of Water . . . . . . 80.00 White fatty matter Red fatty matter Osmazome Albumen. Phosphorus Sulphur and salts, such as 4.53 0.70 1.12 7.00 1.50 * Soemmering distinguishes four substances in the brain, viz., white, gray, yellow, and Dlack. 144 FUNCTIONS OF RELATION. Acid phosphate of potash } lime > . • 5.15 " " magnesia ) The arteries of the brain are large, and are four in number, viz., the two internal carotids, and the two vertebrals; they have a peculiar arrangement, on which we shall more particularly in- sist under the article arterial circulation. We shall only observe here, that they are principally placed at the inferior part of the organ; that, by their anastomoses, they form a circle, and that they are reduced down to capillary vessels before they penetrate into the substance of the brain. It has been computed that the brain receives about one eighth of all the blood which passes from the heart. But this estimate is only an approximation, the quan- tity varying, no doubt, according to a great variety of circum- stances. We know, from recent dissections, that the cerebral ar- teries are accompanied by filaments of the great sympathetic nerve; we can trace these filaments with ease along the princi- pal branches of the arteries. It is to be presumed, therefore, that they accompany them even in their most minute ramifications. But it is not to be concluded, necessarily, from this disposition, which is common to all the arteries, that the brain receives nerves. The filaments of the great sympathetic, have here, as they have everywhere else, an evident connexion with the parietes of the arteries. The cerebral veins have also a peculiar arrangement. They occupy the superior parts of the organ, they have no valvular structure, and they terminate in canals, situated between the lam- inae of the dura mater. We shall particularly investigate this subject under the head venous circulation. No lymphatic vessels have yet been detected in the brain. Observations made on the Brain of Man and living Animals. It has been ascertained from the heads of newborn infants, the cranium of which is still membranous, and from those of adults, where the brain has been denuded by wounds and disease, that it has two distinct movements. -The first is evidently synchronous with the pulsation of the heart and arteries; the second, with res- piration ; that is, the organ seems to sink down upon itself at the moment inspiration takes place ; the opposite phenomenon occurs during expiration. According as the respiration is more or less strong, are these motions of the brain manifest. These two mo- tions are very readily remarked in animals; it is not easy to ex- plain why the existence of this phenomenon should lately have been called in question. It is thought that these motions are very slight when the integrity of the cranium is preserved, and that they are necessary to the perfection of the cerebral functions; but this is a point which has not been demonstrated. The cerebrum, cerebellum, and medulla spinalis, surrounded by the cephalo-spinal fluid, fill exactly the membranes which sur- round them; they exercise even a certain pressure upon their THE ENCEPHALON. 145 surface. This pressure arises from the force with which the blood penetrates the parenchyma, from which it must result that the cerebral substance, incapable of effort itself, is incessantly pressed between the blood and the resistance offered by the mem- branous and osseous envelopes. As the force of the blood varies, according to a number of circumstances, the pressure that the brain must undergo must vary in the same proportion. It appears that this pressure is indispensable to the functions of the organ. If it be suddenly diminished or augmented, the functions are suspended. If the diminution or increase is made gradually, the cerebral functions remain. One of the most simple means of diminishing this pressure is to make a puncture behind the occipital bone, between it and the first vertebra. The ceph- alo-spinal fluid will generally escape in the form of a jet, and im- mediately the cerebral functions will be evidently disturbed. I have, however, seen animals from which I have removed this fluid continue to live without any very apparent derangement of the nervous functions. Examined in a living animal, the brain presents some remark- able properties very different from what might be imagined. Who would suppose, for example, that the greater part of the hemispheres, if not all, is insensible to pricking, tearing, cutting, and even cauterization ? And yet, of this fact, experiment leaves no doubt. Who would think that an animal could live for several days, and even weeks, after the hemispheres had been entirely re- moved ? But many physiologists, ourselves among the number, have witnessed this in different classes of animals. But what is less known and more surprising is, that removing the hemispheres in certain animals, as the reptiles, produces so little change in their usual gait, that it is difficult to distinguish them from sound ani- mals. 11V- Lesions upon the surface of the cerebellum show, also, that this organ is not sensible ; but deeper wounds, especially those which affect the peduncles, are attended with effects of which we shall speak hereafter. But this does not hold true with respect to the spinal marrow; the sensibility of this part of the encephalon is exquisite, with this remarkable circumstance, that it is greatest at the posterior part. much less on the anterior part, and almost destitute of sensibility about the centre of the organ. It is from the posterior part that the nerves arise which are destined to bestow general sensibility. The sensibility is also very vivid on the sides and interior of the fourth ventricle ; but this property diminishes as we approach the anterior portion of the medulla spinalis. It is very weak in the tubercula quadrigemina of the mammiferi. We shall speak here- after of the brain as connected with motion. The uses of the brain in the economy are extremely important and numerous. It is the organ of intelligence ; it is the source of all those means by which we act upon external bodies; it exer- cises an influence," more or less marked, upon all the phenomena T 146 FUNCTIONS OF RELATION. of life, and it establishes a relation, always active, between the different organs; or, in other words, it is the principal agent of the sympathies. We shall now consider it under the first char- acter. Of the Understanding. Whatever may be the number and diversity of the phenomena which pertain to the human understanding, however different they may appear from the other phenomena of life, and though they may be evidently dependant upon the soul, it is indispensable to consider them as the result of the action of the brain, and not to distinguish them, in any way, from other phenomena, which are dependant on organic action. Indeed, the functions of the brain are absolutely governed by the same general laws as the other functions ; they are developed, and they decay, with the progress of age; they are modified by habit, sex, temperament, and indi- vidual character; they are deranged, depressed, and exalted by disease, and the physical lesions of the brain prevent or destroy them. In a word, like every other organic action, they are not susceptible of explanation by us, and in investigating them, laying aside hypothesis, we must be governed by observation and expe- rience alone. It is also necessary to guard ourselves against the impression that the study of the functions of the brain is more difficult than that of the other organs, and that it belongs exclu- sively to metaphysics. By adhering rigorously to observation, and scrupulously avoiding all explanations or conjectures,- this study becomes purely physiological. Perhaps it is even easier than many of the other faculties, from the facility with which we are enabled to produce and examine its phenomena, inasmuch as we have only to turn our attention upon ourselves, to listen or think, so that the phenomena may be subjected to our observation. But this constitutes one of the great difficulties of the subject. That spirit which turns its activity upon itself, which forces itself to know itself, is doubtless a wonderful attribute of man. We owe to this gift many of the advantages we possess. But we find here one obstacle to our insatiable love of knowledge: we cannot overcome certain unsatisfactory notions respecting the phenom- ena which pass in our own understandings. That which occurs in the brains of others is equally beyond our reach, and becomes strongly an object of our conjecture ; we cannot comprehend fac- ulties which we do not possess, or, at least, have but very imper- fect notions of them. This incapacity of knowing that which is not in us, is as true as regards metaphysicians and philosophers as of common men. Whatever desire they may have to describe and class the intel- lectual faculties, they have not succeeded ; for it is not sufficient to announce what has passed in the mind of an individual, but it is necessary to give a general view of what takes place in all. But who would flatter himself that he comprehended precisely the understanding even of the individual who is dearest to him, THE ENCEPHALON. 147 and with whom he is the most intimately allied? who is quite certain that he knows himself? Are we not often surprised at the sudden development of faculties that we did not suspect? Who, then, can undertake, with reasonable hopes of success, to trace the history of the human understanding ? But however this may be, the study of the understanding has not heretofore been considered as constituting an essential part of physiology. One science is specially devoted to this, and is called ideology. Persons desirous of examining this interesting subject in extenso, may consult the works of Bacon, Locke, Con- dillac, Cabanis, and, especially, the excellent work of M. Destutt Tracy, entitled " Elements of Ideology." We shall confine our- selves to some of the fundamental principles of this science. The innumerable phenomena which constitute the human un- derstanding* are but modifications of the faculty of perception. When we examine them with attention, we shall find no difficulty in confirming this observation, the truth of which is generally ad- mitted by modern metaphysicians. We may divide the faculty of perception into four principal modifications: 1st. Sensibility, by which we receive impressions from within or from without. 2d. Memory, or the faculty of reproducing impressions or sensations previously received. 3d. The faculty of perceiving the relation between sensations or judgment 4th. Desire or will Of Sensibility. All that we have said of sensations, generally, will apply to sen- sibility : for this reason, we shall here limit ourselves to observing, that this faculty is exerted in two very different modes. In the first, the sensation passes unobserved by us ; we do not perceive it. In the second we take notice of it, and are conscious of its existence. It is not sufficient, then, that a body acts upon our senses, or that the nerve transmits the impression which it has received to the brain; it is not even sufficient that this organ re- ceives this impression. In order for a perfect sensation to exist, it is necessary that the brain should perceive the impression re- ceived by it. An impression thus perceived is called, in ideolo- gy, a perception, or idea. We may easily prove upon ourselves the existence of these two modes of sensibility. It is easy to see, for example, that a crowd of objects are continually acting upon our senses, without our noticing them. This effect depends in a great measure upon habit. Sensibility varies, infinitely, in different individuals. In some, it is very obtuse; in others, it exists in an extraordinary degree; generally, in those who are well constituted, there is a medium between these two extremes. * The human understanding has been called the spirit, the faculties of the soul, intel- lectual faculties, cerebral functions, &c 148 FUNCTIONS OF RELATION. In infancy and youth, the sensibility is vivid, and remains near- ly in the same state until the adult age; but as old age advances, it becomes materially diminished, so that the decrepit are nearly insensible to all the causes of ordinary sensations. It may be asked, with what part of the nervous system the sen- sibility is most particularly connected. We can now reply, with some precision, to this important question. Already, we have pointed out the class of nerves which, especially, concur in this phenomenon. They are the posterior roots of the compound nerves, and the superior branch of the fifth pair. I have shown, by experiment, that if these nerves are divided, the sensibility of the parts to which they are distributed is extinguished. Experi- ment has equally informed me, that if we divide the posterior fas- ciculi of the spinal cord, the general sensibility of the trunk is abolished. With respect to that of the head, and more particu- larly of the face, and its cavities, I have shown that it depends on the fifth pair. If this nerve be divided before it passes out of the cranium, all the sensibility of the face is lost. The same thing takes place if the trunk of the nerve is cut at the side of the fourth ventricle. Lastly, it is necessary to descend below the level of the first cervical vertebra, that a lateral section of the spinal cord should not be followed by the loss of general sensibility of the face, to- gether with that of the senses. As the origin of the fifth pair ap- proaches near the posterior fasciculi of the spinal cord, which ap- pear to be the principal organs of the sensibility of the trunk, it is probable that there is a continuity between these cords and the fifth pair. But this fact is not demonstrated, either by anatomy or physiological experiments. The principal seat of general sensibility and of the senses is not situated either in the cerebrum or cerebellum. I have given what I regard a satisfactory demonstration of this. Remove the lobes of the cerebrum and cerebellum in one of the mammiferous animals, and then endeavour to satisfy yourself if it is capable of sensations, and you will readily find that it is sensible to strong odours, tastes, and sounds. Thus, it is evident that the sensations are not seated in the lobes of either the cerebrum or cerebellum. I have not cited vision in the above enumeration of the senses. It appears, from the experiments of Rolando and Flourens, that vision is abolished by the abstraction of the cerebral lobes. If the right lobe be removed, the vision is lost in the left eye, and vice versa. The reader may depend upon the truth of this fact, as I doubt- ed for some time its exactitude myself, and was, therefore, indu- ced to verify it by repeating it several times. A wound of the thalamus nervi optici is followed by a loss of vision in the oppo- site eye. I have not found that a wound of the optic tubercle, or anterior quadrigemina, altered vision in the mammiferi; but it is very apparent in birds. In the latter, the abstraction of the hem- ispheres renders the eye insensible to the most vivid light. Thus, THE ENCEPHALON. 149 there are a number of the different parts of the nervous system necessary to vision ; for the exercise of this sense, the integrity of the hemispheres, the optic thalami, perhaps, of the anterior tu- bercula quadrigemina, and of the fifth pair are indispensable. We may remark that the influence of the hemispheres and of the optic thalami is crossed, while that of the fifth pair is direct. If we inquire why the sense of vision differs so much from the other senses, as respects the number and importance of the ner- vous parts which concur in it, we shall find that vision rarely con- sists in a simple impression of light; that this impression may even take place without the existence of vision; that, on the contrary, the action of the optic apparatus is generally connected with an intellectual or instinctive effort, by which we determine the distance, size, form, and motion of bodies; an effort which probably requires the intervention of some of the most important parts of the nervous system, and particularly of the cerebral hem- ispheres. Of the Memory. The brain is capable, not only of receiving impressions, but also of reproducing those which had before existed. This cerebral action, when it produces recently-acquired ideas, is called memo- ry. It is called recollection when the ideas have been long ac- quired. An old man who recalls the events of his youth, recol- lects them; a man who retraces the sensations which he has ex- perienced during the past year, remembers them. Reminiscence is an idea reproduced, which we do not recollect to have previously received. Like sensibility, the memory is very much developed in infan- cy and youth. At this period of life, the mind acquires knowl- edge with the most facility, especially of that kind which does not require much reflection ; such as languages, history, and the descriptive sciences. In the progress of age, the memory be- comes weakened; it diminishes in the adult, and is almost lost in old age. We sometimes see individuals, however, whose memo- ry remains even at the most advanced periods of life. This ad- vantage is, generally, derived from constant exercise, as has been sometimes observed in actors. But it is, undoubtedly, true, that it often exists to the injury of the other intellectual faculties. The more vivid the sensations are, the more easily are they re- membered. The memory of internal sensations are almost al- ways confused. Certain diseases of the brain completely destroy the memory. The memory exercises itself in an exclusive manner, if I may be allowed the expression, on different subjects. There is a mem- ory of words, of places, of forms, of music, &c. It is rare that an individual unites these different memories ; they are generally iso- lated, and almost always form a striking trait of the understand- ing, of which they constitute a part. Diseases sometimes present psychological analyses of the memory ; one patient may lose the 150 FUNCTIONS OF RELATION. memory of proper names, another of substances, a third of num- bers, and cannot count above three or four ; or he may lose the memory of language, and the faculty of expressing himself on any subject. Generally, in these cases, after death, lesions are found to a greater or less extent in the brain or medulla oblongata. But morbid anatomy has not established a direct and constant re- lation between the diseased part and the kind of memory abolish- ed, so that we are still ignorant if there exists any part of the brain which is more particularly destined to the exercise of memory.* Of Judgment. There can be no doubt that judgment is the most important of the intellectual faculties. It is by this faculty that we acquire all our knowledge. Without it, our life would be purely vegetative, and we should have no idea of the existence of other bodies, or even of our own, as all our knowledge is the direct result of the faculty of judgment. To form a judgment is to establish a rela- tion between any two ideas, or collections of ideas. When I judge that a work is good, I perceive that the idea of goodness agrees with the book which I have read; I establish a relation, I form an idea different from what sensibility or memory would have en- abled me to form. A series of judgments connected together constitute reasoning. We may readily conceive how important it is for us to form correct judgments, that is, that we do not es- tablish any relations but those which really exist. If I judge a substance which is poisonous to be salutary, I incur the danger of losing my life ; the false judgment which I have formed will be very injurious to me. The same remark will apply to all false judgments. Nearly all the misfortunes to which man is exposed, morally speaking, have their origin in errors of judgment; crime, vices, and bad conduct, are all, the results of false judgments. It is the object of one science, viz., logic, to teach us to reason justly. But sound judgment and good sense, or erroneous judg- ment and mental weakness, are the results of organization. It is impossible to change in this respect; we must remain as nature has formed us. Some men are endowed with the valuable gift * Phieaology, a pseudo-seience of the present day -r like astrology, necromancy, and al- chemy of former times, it pretends to localize in the brain the different kinds of memory. But its efforts are rtiere assertions, which will not bear examination for an instant. Cra- niologists, with Dr. Gall at their head, go even farther ; they aspire to nothing less than determining the intellectual capacities by the conformation of the crania, and particularly by the local projections which they remark. A great mathematician presents a particular elevation about the orbit; this is said to be-the organ of calculation. A celebrated artist has a large bump on the forehead; that is the seat of his talent. But, replies some One, Have you examined many heads of men who have not these capacities ? Are you sure that you do not meet with the same projections, the same bumps ? That is of no consequence, replies the craniologist; if the bump is found, the talent exists, only it is not developed. But here is a great geometrician, or a great musician, who has not your bump. No matter, replies the sectary, you must believe. But, replies the skeptic, the aptitude should always exist, united with the conformation, otherwise it will be difficult to prove that it is not a mere coincidence and that the talent of the man depends really on the particular form of hisi cranium. Still, replies the phrenologist, believe ! And those who delight in the vague and the marvellous, do believe. There is some show of reason in this, for they thus amuse themselves, while the truth would only cause them ennui. THE ENCEPHALON. 151 of discovering relations which have never before been perceived by others. If these relations should happen to be important, so as to confer great benefit on mankind, their possessors are said to be men of genius; but if they relate to objects of less importance, they are said to possess wit, or imagination. It is principally by their manner of perceiving relations, or judging, that men differ from each other. Vivacity of sensation appears to be injurious to cor- rect judgment; this is the reason why this faculty becomes more perfect with age. We are ignorant of the part of the brain which is the particu- lar seat of judgment. It has been long believed to be in the hemi- spheres, but nothing directly proves this. Of the Desire, or Will. We give the name of will to that modification of the faculty of perception by which we experience desires. In general, it is the consequence of our judgment, and it is worthy of remark, that upon this faculty our happiness or unhappiness necessarily de- pends. When our desires are satisfied, we are happy; we are unhappy, on the contrary, when we cannot gratify them. It be- comes us, therefore, so to direct our desires that we shall be enabled to gratify them. We must avoid desiring, for example, those things which it is impossible for us to obtain; and it is still more important for us not to desire those which are injurious, for in this case we cannot escape unhappiness, whether we indulge them or not. Morality is a science, the object of which is to give the best possible direction to our desires. Desires have been gen- erally confounded with that cerebral action which presides over the contraction of the voluntary muscles. I think it advantageous to the student that this distinction should be established. Such are the four principal distinctions into which the faculty of perception has been divided; they have been called the simple faculties of the mind. It is the combination and reaction of these faculties upon each other which constitutes the understanding of man and the higher order of animals. There is, however, this remarkable difference between man and other animals : they re- main always in nearly the same state, their faculties receiving but little improvement in the course of their lives; but man derives improvement from every object by which he is surrounded, and is thus enabled to attain that intellectual superiority by which he is distinguished. The faculty of generalizing, which consists in creating signs to represent ideas, to assist thought by means of these signs, and to form abstract ideas, is characteristic of the human understanding. It is this which enables it to acquire that prodigious extension which we see in civilized nations. The faculty of generalizing can, of course, only exist in a state of society. An individual who should have lived alone, and who should not have had any inter- course with his fellow-creatures, even in his early years, of which there have been several examples, would not differ much from 152 FUNCTIONS OF RELATION. brute animals ; he would only possess the four simple faculties of the mind. It is the same with those individuals to whom nature, by a defective organization, has denied the faculty of employing signs, or of forming these abstract or general ideas ; they remain all their lives in a perfect state of brutality, as we observe in idiots. In genera], the physical circumstances in which a man finds himself placed will have a powerful influence upon the develop- ment of his understanding. If he is enabled to procure subsist- ence with ease, and to satisfy all his physical wants, he will be in a situation favourable to the cultivation of his mind and a free de- velopment of his mental faculties; but if he can only, with diffi- culty, satisfy the demands of nature, his mind, being chiefly direct- ed to that single point, will necessarily remain in a rude and im- perfect state, as is always found to be the case among savages and slaves. The intelligence of man is limited by the number of his facul- ties, and the degree of development of each. No one can pass be- yond the point allotted to him by his organization. It is in vain that he endeavours to acquire those aptitudes which nature has not granted to him. But each one, by exercising the faculties that he does possess, may extend them, and carry them to a de- gree of perfection far beyond that at which they would have re- mained if they had not been frequently exercised. This is the important end to which education should be directed. Certain philosophers, or, rather, dreamers, have supposed that all men are born with equal intellectual capacity, and that educa- tion, and the circumstances in which they may have accidentally been placed, determine the differences that we observe ; but no- thing can be more erroneous than this supposition. From the idiot, who is incapable of eating without assistance, like an infant at the breast, to the man of genius, whose discoveries ameliorate the social condition, there are an infinite variety of shades, which constitute the individual lot of humanity. One man possesses all his faculties, but in a minimum degree; another has many emi- nent faculties, while he is inferior or incapable as it respects the others; a third has but one faculty, if I may be allowed thus to express myself, while the others are so defective that he appears to be destitute of them ; lastly, there are privileged men, in whom nature has combined, in a high degree, all the capacities of the human mind. These men, so happily constituted, enjoy immense advantages unknown to the rest of mankind. They may, for ex- ample, comprehend everything, and make themselves understood by all, which is not permitted by common intelligences. These complete men are rare. What is true of men, taken individually, without distinction of race, holds true also as respects the varieties of the human species. The descriptions of travellers and historians have enabled us to form a sort of scale of intellectual capacity, from the Caucasian variety, to which we belong, to the ferocious and brutal savage THE ENCEPHALON. 153 of the Southern islands, who has never raised himself above the use of his canoe. The different states of civilization, observed among the numerous races of men scattered over the surface of the earth, may thus be considered, not merely accidental shades, the consequences of manners, customs, and climates, but the im- mediate and necessary results of organization. It might appear necessary next to enumerate and describe, suc- cessively, the different faculties of the human understanding; but I have already explained, above, the reasons why this attempt has been heretofore confined to the most distinguished metaphysicians. It would, therefore, be most rash for us to undertake an object so difficult, and, perhaps, impossible to accomplish. Man acquires his ideas and knowledge of the objects which surround him by means of his senses and intelligence ; this consti- tutes his learning or acquirements, the extent of which varies ac- cording to his aptitudes and the exercise they have received, that is, his experience. It depends upon ourselves, with the faculties with which we are endowed, to acquire more or less knowledge, and to augment thus the intensity of our existence and the chances of our happiness; for, generally speaking, men's happiness in- creases with their intelligence. Unhappiness, on the contrary, for the most part, originates in ignorance. There are many things over which our minds have no control, but which, nevertheless, deeply interest us. Urged on by that admirable faculty by which we are prompted to seek for causes, we often imagine we have succeeded, when everything shows the importance of our efforts; or we admit that which has been ima- gined by others possessed of bolder and more fertile spirits. Thus are formed hypotheses, systems, doctrines, creeds, which divide, with learning, the attention of men, and which often en- gross the best minds. Thus the sum of ideas that our intelligence procures us is com- posed of that which is real, or which we know, and that which we believe, or imagine, or have admitted without proof; in other words, that of which we are ignorant. Thus, to believe, or to create a system or doctrine, is, rigorously speaking, but to be ig- norant. I am far from pretending that all that we believe is ne- cessarily false or merely imaginary. Undoubtedly that which we believe may be true and real, but it only acquires this char- acter to us when it is capable of being verified by experimental proofs. In this respect, mankind may be divided into two classes, which are destined always to remain distinct from each other. The ob- ject of one is positive, experimental truth; the other is satisfied with that which is vague, fanciful, wonderful, perhaps even ab- surd. They attach more importance, and feel deeper interest, as their belief is their own peculiar work, adapting itself perfectly to their minds—making, in some sort, a part of themselves; they maintain it with warmth, energy, extreme tenacity; it is impos- sible to demonstrate to them that they are in error. U 154 FUNCTIONS OF RELATION. These two classes of minds have shown themselves, though with different results, in all those pursuits connected with the in- telligence of man. The first have founded and perfected the sciences, and all positive human knowledge ; the second have shone, with a brilliant light, in the arts of imagination: that ca- reer is their peculiar domain. But, unfortunately, it has often happened that those who possess the latter class of minds have also cultivated natural philosophy ; but so far from promoting its progress here, as in other instances, ideas are made to supply the place of facts ; the offspring of their imaginations become the great phenomena of nature. Dangerous energy ! barren zeal! which tend to annihilate these very sciences, and to erect in their place fantastic images, which vanish before the first examination of a positive mind, the friend of reality. Of Instinct. Nature has not abandoned animals to themselves. It is neces- sary that each should exercise a series of actions, from which re- sults that astonishing harmony which we witness among organized beings. To induce animals to concur in this, and to execute those actions for which each is designed, nature has given them in- stinct ; that is, desires, inclinations, wants, by means of which they are continually and forcibly compelled to fulfil the designs of nature. Instinct may exist in two different ways, viz., with or without a knowledge of the end. The first may be called intelligent i%r stinct; the second, blind, or brutal instinct. The first is more par- ticularly the prerogative of man; the second pertains to animals. In examining, with care, the numerous phenomena which depend upon instinct, we find that it has two principal objects; the first is the preservation of the individual, and the second that of the species. There are as many instincts as species of animals, vary- ing according to their organization. As organization varies among individuals, these instincts are much more remarkable in some than others. In man, we find two kinds of instincts: the first relates to his condition as an animal, and is always exhibited by him in what- ever situation he is found. This kind of instinct resembles that of animals. The other arises from the social state. Without doubt it depends, like every other vital phenomenon, upon orga- nization. But this is never developed but in a state of civil socie- ty ; for this purpose, it is necessary that he should enjoy those ad- vantages which accompany this state. The first, which may be called animal instinct, includes hun- ger, thirst, a want of clothing, and habitation; a desire of happi- ness, or of agreeable sensations, and the fear of pain and death; a disposition to destroy other animals, or even those of his own species, when dangers are to be feared from them, or advantages to be derived from their destruction; the venereal appetite; at- tachment to children ; tendency to imitation; and a love of soci- THE ENCEPHALON. 155 ety, which leads to civilization, &c. These instinctive sentiments are constantly acting upon man, and induce him to concur in the order established among organized beings. The natural wants of man are more numerous and various than those of other ani- mals, in a direct proportion to his intelligence. In every other respect he enjoys a decided superiority over all other animals. When man lives in a state of society, he is enabled easily to satisfy all the wants of which we have been speaking; he has then leisure ; in other words, to satisfy these first wants, requires but a small portion of his time and faculties. Then arise new wants, which may be called social. Such is our desire to have a very vivid consciousness of our existence ; a feeling which, the more it is indulged in, the more difficult it is to satisfy, because, as we have already observed, our sensations become weakened by habit. ; This fondness for vivid impressions, joined to a continual dimi- nution in the strength of our sensations, causes inquietude and vague desires, which are increased by the importunate recollec- tion of the vivid sensations that we formerly experienced. For the purpose of removing this state, we are compelled to have re- course to a continual change of objects, or to increase the inten- sity of the same sort of impressions. From this arises an incon- stancy, which does not permit us to fix any limits to our wishes, and a progression of desires which are annihilated by indulgence, but afford us no gratification; hence arises ennui, that unceasing source of misery to civilized man when he has no employment. This desire of vivid sensations is counterbalanced by a love of repose, or indolence, which acts so powerfully on the higher classes of society. These two opposite sentiments modify each other, and from their action and reaction result a love of power, of consideration, and of wealth, which enables us to indulge both. These two instinctive sentiments are not the only ones which arise from the social state; it develops a crowd of others, less important, indeed, but not less real. Our natural wants, also, be- come remarkably altered; instead of hunger, a most capricious taste is often substituted; for the venereal desire, feelings of a very different nature, &c. Natural, modify social wants, and vice versa; and when, in addition to this, we recollect that age, sex, temperament, &c., have a strong influence upon all our desires, we may form some idea of the difficulties which a study of the in- stinct of man presents. This part of physiology has been hereto- fore scarcely noticed. We may at the same time remark, that an increase of the so- cial wants is always accompanied by a corresponding develop- ment of the understanding. There is no comparison, as relates to the capacity of the mind, between man in the more opulent class of society, and as he is found in that condition where all the physical energies are barely sufficient to provide for his first wants. The innate dispositions or instincts particularly occupy the phrenologists at the present time. Their efforts are especially 156 FUNCTIONS OF RELATION. directed towards the triple end of recognising and classifying the instinctive dispositions, and assigning the distinct organs in the brain. But it must be admitted that thus far there is little appear- ance of success. Of the Passions. In general, we understand by the term passion an extreme and exclusive instinctive sentiment. A man in a passion neither sees, hears, nor is conscious of anything but the sentiment by which he is excited; and as the violence of this sentiment ren- ders it disagreeable, and even painful, it has received the name of passion or suffering. Passions have the same end as instincts; they induce animals to act according to the general laws of liv- ing bodies. We see in man passions, which he has in common with other animals, which consist in vehement animal desires; and others which display themselves in a state of society only; these are.the social wants very much increased. The animal passions relate to a double end, as we have before remarked, in speaking of natural instinct, viz., the preservation of the individual and that of the species. To the preservation of the individual, belong fear, anger, grief, hatred, and excessive hunger, &c.; to that of the species, the venereal appetite, jealousy, and furious anger, when the offspring is in danger. Nature has attached great importance to this class of passions, which exist in their full force in man in a state of so- ciety. The passions peculiar to a state of society are but the social wants carried to an extreme degree. Ambition is but the excess of a love of power; avarice, an excessive desire of fortune; hatred and vengeance are but natural and impetuous wishes to injure those who have injured us; a passion for play, and almost every other vice, are the results of a love of violent excitement; violent love is but an exaltation of venereal desires, which agitate, per- vert, and often animate us with ineffable pleasure, &c. Among the passions, some weaken or extinguish themselves when they are satisfied; others, again, increase by indulgence. Happiness is often produced by the first, as we sometimes see in love and philanthropy; but unhappiness is necessarily attached to the last, examples of which are constantly furnished by the am- bitious, avaricious, and envious. If wants develop the powers of the understanding, the passions are the principal cause of everything very great which has been accomplished by man. The great poets, heroes, criminals, and conquerors have always been men who were strongly under the influence of the passions. In speaking of the passions, shall we say, with Bichat, that they reside in the organic life, or, with the ancients and some moderns, that anger is in the head, courage in the heart, and fear in the semilunar ganglion, &c. ? Passions are but internal sensations ; CEREBRUM AND CEREBELLUM. 157 they cannot, therefore, be said to have a seat; they result from the action of the nervous system, particularly of the brain; they do not, therefore, admit of explanation. We are capable of ob- serving, directing, calming, or extinguishing, but not of explaining them. CHAPTER X. OFFICES OF THE CEREBRUM AND CEREBELLUM. [Intellection is the most remarkable office of the encephalon. Thought, perhaps, is not necessary to the existence of animals, though some degree of it seems implied in all endued with the power of voluntary motion. In the lowest orders of animals no distinct encephalon exists; but, as we rise in the scale, we find these organs bestowed. They are at first in a simple form, but gradually attain their highest development in the vertebrated ani- mals. The large nervous masses constituting the encephalon are, no doubt, the centres of the nervous system and the seat of intel- lection, the cerebrum appearing to be more particularly appro- priated to this latter office. It does not necessarily follow that the power of an organ should always increase with its size, as in some instances the organ more than makes up for its want of size by the energy of its vital actions. These, however, are but ex- ceptions, it being a general law of the animal economy that the size and development of an organ are indicative of its relative power. Agreeably to this rule, the most cursory observation shows that generally a striking relation does exist between the volume and form of the encephalon, and the manifestations of in- tellection, in different animals. The mass of the encephalon, in proportion to that of the rest of the body, is, generally speaking, greater in man than in other animals, though there are exceptions. It is also generally, though not, perhaps, invariably, true that the encephalon in him is larger, in proportion to the other parts of the nervous system, than in other animals. The nerves, the immediate instruments of the senses, by which ideas of surrounding objects are collected, are larger and more developed in other animals ; but the encephalon, the organ of intellection, in which ideas derived by means of the senses appear to be combined, and, as it were, wrought up into thought by reflection, is relatively much more ample in man. It is also generally, if not invariably, true, that the degree of intelli- gence in animals is indicated by the development of the cere- brum, especially the anterior lobes. It is on this postulate that craniology rests. The facial angle of Camper is liable to the obvious objection that it only pretends to make us acquainted with the capacity of 158 FUNCTIONS of relation. the cranium from its anterior to its posterior part, but takes no notice of its lateral expansion. Still, it is admitted to be a general index of the intellectual power, not only of different animals, but of the different varieties of the human race, and even individuals. Dr. Gall and his followers have gone a step farther, and alleged that the cerebrum consists of a collection of organs, and, accord- ing to their development, form corresponding cranial prominen- ces ; so that, by examining the cranium, an experienced observer can determine not only the degree of intellection, but the mental peculiarities and propensities of an individual. The first aspect of these doctrines is certainly extravagant and visionary, and, as has been complained even by some who have adopted them, have been carried to an extreme. Still, there has been a spirit of in- quiry awakened, and the subject has been pursued with an enthu- siasm by some gifted minds, among whom may be named Dr. Cald- well, of Kentucky, which has thrown light upon the physiology and pathology of the nervous system, and is deserving of some farther notice. One of the circumstances that has tended particularly to give currency to these doctrines is the isolated character of several of the intellectual faculties. Some of them are separable from each other by clearly-defined lines in the normal state, and are some- times modified or abolished by disease, while the other faculties are scarcely disturbed. We may mention the loss of the mem- ory of words as one of the most striking examples of this. The organ of speech is stated by Spurzheim to be situated in the ante- rior lobes of the cerebrum. Now it has been alleged, that, in fa- tal cases of apoplexy attended with this sympton, loss of memory of words, appreciable organic lesion of the anterior lobes is gen- erally found. Bouillaud states that four cases where this coinci- dence occurred came under his own observation. He farther re- marks, that, on a careful examination of the numerous cases of cerebral affections collected by Lallemand and Rostan, he found thirteen similar cases. Such, he states, was the uniformity of this coincidence, that, after reading the symptoms of a case, from the presence or absence of it, he could pronounce with accuracy whether lesion of the anterior lobes had or had not been found. After making this statement, Bouillaud exclaims, with his charac- teristic enthusiasm, " How can this truth be hereafter contested, inasmuch as it is thus established by direct observation; first, that speech was disordered or completely destroyed when the anterior lobes were affected; second, that speech continued when the le- sion was situated in other parts of the cerebrum ?"* But farther inquiry has shown the necessity of greater caution in such gen- eralizations. Remarkable as these facts appear, farther inquiry has proved that they were mere accidental coincidences. Thus, a case has since been related by Cruveilhier where the anterior lobes were entirely wanting, in a case of congenital malforma- tion, in which the patient had been idiotical from birth, and in * Bouillaud, d'Encephalite, p. 168. CEREBRUM AND CEREBELLUM. 159 whom almost the only indication of intellect was the power of ar- ticulation.* Numerous cases have also since been observed in which the anterior lobes were disorganized without loss of speech, and the reverse. In thirty-seven cases of cerebral hemorrhage of one of the anterior lobes, observed by Andral, twenty-one were accompanied by loss of speech, while in sixteen it was preserved; in seven, where the hemorrhage was confined to the posterior lobes, speech was abolished in all; and in seven others, where it was confined to the middle lobes, there was also loss of speech in all.f It has been observed, also, that comparative anatomy is opposed to the doctrines of the phrenologists. It is a curious circumstance that the difference in the antero-posterior diameter between the brain of man and that of the lower mammalia principally arises from the shortness of the posterior lobes in the latter, these being seldom long enough to cover the cerebellum; yet it is in these posterior lobes that the animal propensities are regarded by phre- nologists as having their seat. On the other hand, the anterior lobes, in which the intellectual faculties are considered as residing, in many animals bear a much larger proportion to the whole bulk of the brain than they do in man.J Another of the fundamental assumptions of craniology is, that the ossific textures have no independent power of development, but are moulded to the forms of the soft parts. Hence, as is al- leged, the irregularities on the inner surface of the cranium, and those external prominences which mark the localities of the or- gans. But there are reasons for believing that the cranium pos- sesses an inherent power of development, and that the irregulari- ties of its surfaces referred to are attributable to this power, and not to their being moulded to the form of the brain. The case of Cruveilhier, above referred to, may be cited in proof of this. The subject, a female, died at the age of fifteen, having been idi- otical from birth. The external appearance of the cranium was natural; but, on removing it, the anterior lobes of the cerebrum were altogether wanting, their place being occupied by a gelati- nous fluid ; yet the inner surface of the cranium presented irregu- larities similar to other skulls. But though phrenology is by no means without objections, yet it is admitted to be an ingenious and plausible hypothesis, and to have found able defenders and ardent admirers among some gifted members of the profession. But other inquiries have been instituted for the purpose of de termining the portion of the brain in which intellection is per- formed, without pretending to ascertain the exact seat of each faculty or desire with the particularity affected by Dr. Gall and his followers. Among those who have investigated this subject with the most ability and zeal, and whose facilities for observation were the best, may be mentioned Foville, Pinel, Grand Champs, and Bouillaud. All these distinguished pathologists have agreed * Cruveilhier, Anat. Path., liv. viii. t Andral, Pathol. Interne, t. iii, p. 98. X Carpenter. 160 FUNCTIONS OF RELATION. in the opinion, derived from observing the effects of disease, that the whole of the cortical substance of the hemispheres, and es- pecially the anterior lobes of the cerebrum, are the parts in which intellection is more particularly executed. This was not so broad- ly advocated by Sir Charles Bell, though it would appear that he leaned to this view. An opinion has long' been entertained by physiologists, that the number and size of the convolutions of the brain, and especially the depths of the furrows between them, are indicative of the in- tellectual power of the individual. Malacarne had noticed that the convolutions in the brains of idiots are smaller in size, fewer in number, and the anfractuosities less strongly marked than in other persons. The comparative intelligence of the inferior ani- mals is remarked to be much more accurately indicated by the convolutions of the brain than the capacity of the cranial cavity. Their intelligence is also alleged to diminish in proportion to the decrease in the gray or cortical substance of the brain. In the foetus the gray substance is scarcely found, but increases as the intellectual powers are developed; while in old age it is said to diminish with the fading powers of the mind. The suggestion, therefore, that this portion of the cerebrum is more particularly the seat of intellection, seems a natural corollary from these premises. The experiments of Flourens, some of which are very remark- able, have had great influence in giving confidence to the opinion that the periphery of the cerebrum is more particularly the seat of intellection. Of a great number of experiments, represented as being attended with similar results, we shall refer here but to one. " He removed the two cerebral lobes of a hen, at the same time carefully avoiding those inferior portions of the lobes connected with the roots of the olfactory nerves. The bird was immediate- ly deprived of vision and hearing, and fell into a stupor. It re- mained in this state, merely taking a little water, which was pour- ed down its throat, until the third day, when it began to revive, and was ultimately restored to good health. But it appeared to be perfectly unconscious of everything that took place about it. It appeared entirely destitute of taste, smell, vision, or hearing. It never made any effort to eat or drink. It could walk, but if it met any object it did not appear to know how either to avoid or go away from it. It digested the food that was forced down, and even grew fat. Though apparently destitute of intelligence, the locomotive powers of this animal were completely preserved. It could walk, run, and fly. It survived this loss of its cerebral lobes six months, and then was killed. Though deprived of its senses, its organs of sense appeared perfect. The eye was as clear and natural in appearance, and the iris preserved its motion as before." But if the surface of the cerebrum, and particularly its anterior lobes, be the seat of intellection, we should naturally expect that an inflammation, or other morbid state of these parts, would ne- cessarily be followed in every case by disorder of this function. CEREBRUM AND CEREBELLUM. 161 Still, it is universally admitted that this does not by any means uniformly occur. Where the lesion is confined to one hemisphere, this has been plausibly, if not satisfactorily, explained by the symmetrical character of the encephalon. It has been said, like the eyes, or the ears, or other symmetrical organs, that when one side of the encephalon was affected, the office of intellection might be executed by the other. The wisdom and benevolence of this arrangement have been eloquently dwelt upon by Bouillaud. We shall not deny that each half of the encephalon is capable, like the other symmetrical organs, of acting, to a certain extent, inde- pendently. We may remark, however, that the analogy is not complete. But admitting this explanation to be sufficient where the path- ological condition is confined to one hemisphere, if we consider the cerebrum as the seat of intellection, how shall we account for the uninterrupted execution of this function where considerable organic lesion of the greater part of the periphery of the cere- brum and of its anterior lobes exists ? This is no doubt a rare event, yet it undoubtedly sometimes occurs. The following interesting case is related by Dr. Boerstler, of Lancaster, Penn- sylvania, in an excellent letter addressed by him to Professor Dunglison, published in the first number of the " Medical Library and Intelligencer," edited by the latter gentleman. The whole case, including the treatment, is published at length. We have only extracted those parts which have a direct bearing on our present inquiry. It is strikingly opposed to the views of Bouillaud and others, that " when the two hemispheres are profoundly alter- ed, the intellectual and moral faculties are abolished, and sensation and voluntary motion paralyzed, the patients resembling those animals in which the lobes had been removed."* " The patient was a lad about eleven years of age, who, in con- sequence of a kick from a newly-shod horse, had the superior portion of the os frontis and the anterior portion of the right pari- etal bone fractured. One portion, an inch and a half long, was driven into the anterior lobe of the cerebrum to the depth of an inch, in removing which a tablespoonful of brain was dischar- ged. There was great laceration of the meninges, from the rag- ged edges of the bony fragment. The integument was lacerated and bruised, and sloughed in a few days, leaving a considerable portion of the scull and cerebrum exposed." There was some intellectual confusion at first, but " at the end of two hours he recovered every faculty of the mind, and they con- tinued vigorous for six weeks, and to within one hour of his death, which took place on the forty-third day. During all this period there was little apparent derangement in any of the organs, ex- cept a slight irritative fever, which supervened sixteen days after the injury, and continued to the termination of the case. So slight, however, was the indisposition, that the patient sat up every day, and frequently walked to the window to see the boys play in * Bouillaud, d'Encephalite, p. 266-7. X 162 FUNCTIONS OF RELATION. the street, in which he took a deep interest, frequently laughing at their gambols." " Four hours after death the body was examined by Dr. Boerst- ler, in the presence of Drs. Ohr, Edwards, and Newcomer. Upon removing the cranium, the dura mater presented strong marks of inflammation over the entire arch of the head, being deeply injected in some parts, and having depositions of coagula- ble lymph in others. The dura mater was ulcerated at three points. The space previously occupied by the right, anterior, and middle lobes of the cerebrum presented a perfect cavity, the hollow of which was filled with sero-purulent matter, the lobes having been destroyed by suppuration, and the third lobe much disorganized. The left hemisphere was in a state of ramollisse- ment down to the corpus callosum. It was so much softened that the slightest touch would remove portions, and with the aid of a sponge I wiped away its substance near to the corpus callo- sum, when it became firmer, but presented the appearance more of a homogeneous mass than of regular organization. The chiasm of the optic nerves, as well as their entire tract, was so soft as to yield to a slight touch with the handle of the scalpel, and the ol- factory nerves were in the same condition. The corpus callo- sum, thalami nervorum opticorum, and tubercula quadrigemina were in a physiological state. The cerebellum presented no path- ological condition; the spinal column was not examined." " This boy was remarkably intelligent. In my daily visits I held frequent conversations with him, and in all my observations I could not discover the slightest derangement of his intellectual faculties ; no dulness of sensibility, no obtuseness of perception, no impairment of judgment, no want of memory, and, so far as mind was concerned, he gave no evidence of disease. His vision, au- dition, and voice were unimpaired." This well-authenticated case is of itself sufficient to unsettle our confidence in all those speculations respecting the functions of the superficial and superior portions of the cerebrum, especially the anterior lobes, which have been so generally received. It seems to show that these parts are far from being exclusively the seat of intellection and indispensable to the offices of the organs of the senses, as was alleged by Flourens. The anterior and middle lobes of the right side were completely destroyed, and the third much disorganized, yet, contrary to the almost universal experi- ence and opinions of modern physiologists, there was no appre- ciable alteration in the senses or power of voluntary motion in the opposite side. The lobes of the left hemisphere were not so absolutely destroyed, yet the disorganization was such as would lead us to expect abolition of their functions. It is evident, how- ever, that we have much to learn respecting the effects of soften- ing of the textures, especially the cerebral, in weakening or abol- ishing the functions of a part. This kind of disorganization has only within a few years excited the attention of pathologists. The mode in which ramollissement of the encephalon arises, and CEREBRUM AND CEREBELLUM. 163 the precise nature of this pathological condition, are by no means satisfactorily ascertained. Sometimes it appears to arise from inflammation, but at others it does not. It has been compared to gangrene, but the history of this case seems opposed to such an opinion. The autopsic examination was made so early after death as to remove every reasonable doubt as to its having ex- isted during life, and probably for a considerable time. Other cases, though perhaps no one so conclusively, have shown that ramollissement of the encephalon may exist without abolition of function. The state of the chiasm of the optic nerves and of the olfactory nerves proves this beyond doubt. A vast number of experiments were made by Rolando, SerreS, Le Gallois, Flourens, Desmoulins, and Magendie, on living ani- mals, for the purpose of determining precisely the functions of the different portions of the encephalon. Their experiments were generally ingeniously designed, skilfully executed, and in some instances the results were curious and interesting. One of the most remarkable circumstances is the great restorative power of the animal economy in overcoming extensive mutilations of these most important organs. But when they are carefully analyzed, they do not throw as much light on the objects of their investiga- tion as might have been anticipated, and very little on the seat of intellection in the human subject. There are some grave objec- tions to this mode of investigation; the pain that must be necessa- rily inflicted, and the disorder induced in all the functions conse- quent upon these sufferings, must essentially influence the results ; while the great difference which manifestly exists between the functions of these organs in man and the inferior animals, allows little weight to any inferences that may be drawn with respect to the former. The results of these experimental inquiries are also different, and in some points opposed to each other; and while they prove how unsatisfactory this mode of investigation is, they also show the difficulty of the subject, and how little we at pres- ent understand it. Nor are the results of our inquiries on this subject derived from pathalogical anatomy much more satisfactory. The causes of obscurity are different, but perhaps as great Lesions resembling each other in locality and extent are attended with widely differ- ent symptoms; while in some cases apparently a change of struc- ture limited in extent and trifling in degree, is attended with the most alarming and fatal consequences; in others the most exten- sive disorganizations may continue for years, without scarcely disturbing the harmony of the functions. A case is mentioned by Dr. Abercrombie of a female who, from the history of the case, had been evidently labouring under a chronic affection of this kind for four years, yet the functions of intellection, sensation, and vol- untary motion were not essentially disordered. Similar observa- tions have been made as respects chronic hydrocephalus ; the ven- tricles have been found so distended that the cerebral matter has seemed like a thin lamina, spread over the interior of the crani- 164 FUNCTIONS OF RELATION. urn. It is very remarkable that sudden injuries of this organ, even though slight, are often followed by the most violent symp- toms ; while in chronic diseases extensive changes of structure may occur with but trifling external indications. But if any def- inite portion of the cerebrum be exclusively concerned in intellec- tion, we should naturally expect to find indications of it on ex- amining the bodies of those who have died after having suffered long from mental alienation. Until very recently, however, it has not been pretended that any uniformity in the cadaveric ap- pearances could be traced in this disease. Morgagni, the mosl accurate of the older pathological anatomists, acknowledges that he could find nothing uniform or characteristic of mental aliena- tion, while Pinel and Esquirol expressly declare that pathologi- cal anatomy of the brain threw but little light upon the disease. In 259 dissections of maniacs, made under the supervision of Messrs. Esquirol, Villemain, Beauvais, and Schwilgae, only 68 were found to exhibit any appreciable indications of lesion of the brain.* M. Esquirol seems to have attached more importance to the form, thickness, density, &c, of the cranium than to any other pathological appearance about the heads of maniacs. More recently, however, Foville, Calmeil, and Falret, have en- deavoured to show that certain appreciable changes of structure do occur with great uniformity in the encephalon of maniacs. M. Foville has especially described certain changes in the structure of the cortical substance, which he thinks may be traced with great regularity in this class of patients. One of the most uni- form of these appearances is an induration of the surface of the brain, in consequence of which, this thickened and hardened por- tion of the cortical part may be detached like a thick, dense mem- brane. He says that an obvious difference in density is observ- able between the cortical substance thus detached and that un- derneath, which may be recognised by scraping them with a scalpel. He alleges, though he had frequently made examina- tions of persons dying of other diseases, that he had never observ- ed this appearance, but that he had noticed something similar in the brains of a hyena and a badger, both of which died in a state of captivity. He also alleges that he had found combined with this harden- ing of the superficial lamina of the cortical substance of the brain various modifications in its colour and appearance, while the form and size of the convolutions had undergone a marked change; their upper part in many cases appearing to have fallen into a state of atrophy, which gave to them an appearance as if they had been pinched up between the fingers in some instances; in others, the loss of substance was about their base; while again, in some cases, scarcely any vestiges of the convolutions remain- ed. In these cases of atrophy, the gray substance was gener- ally more firm than natural, while in many instances it had be- come so pale, that he found it difficult to distinguish the limits be- * See Med. Chir. Rev., v. x., and Borrowe on Insanity. CEREBRUM AND CEREBELLUM. 165 tween the cineritious and medullary portions. In some cases, however, the cortical substance was softened instead of being hardened. Some alterations are also mentioned by M. Foville as having been observed in the colour and density of the medulla- ry portions of the brain and the meninges. With respect to these observations, we may remark, that at present they may be considered as proper subjects of inquiry, not as points in pathological anatomy that are already established. That some of these and other morbid appearances are sometimes found in various parts of the brains of maniacs, there can be no doubt; the question is as to their uniformity. Though M. Fo- ville and others think they have discovered certain appearances which occur with great regularity, yet they are at issue on this point with some of the highest authorities in the profession. There is but one other condition of this organ to which we shall at present refer to elucidate this question—the precise seat of intellection. It is to those cases which we occasionally meet, where certain parts of the cerebrum have not become developed, or have fallen into a state of atrophy. We have already referred to one case of this kind by Cruveilhier, in which there was a con- genital deficiency of the anterior lobes, accompanied with idiocy and inability of progression. Breschet has recorded three cases where there was this defect in the organization: one was blind, but possessed sensation, and the power of voluntary motion; and one was idiotical, and destitute of vision and olfaction. In an- other case, the posterior lobes were deficient, and the person idiot- icaL Cases are also referred to by Andral (Pathol. Intern., t. iii., p. 114) of atrophy of the corpus callosum and pineal gland, the latter diminished to the size of a millet seed, the rest of the enceph- alon being in a normal state, also accompanied by idiocy. Thus it appears that defective development, or atrophy, not only of the anterior lobes, but various other parts of the brain, may be accom- panied by idiocy. Nothing positive can be inferred from these facts, therefore, as to the seat of intellection. From what has been said, we are led to infer that intellection is chiefly executed by the cerebrum, although, as will be hereaf- ter seen, there is reason for thinking that some acts, that may be properly referred to this head, are dependant upon the cerebellum. It is quite certain, at least, that these organs are intimately asso- ciated in function as well as structure. From the premises, it would also appear that, in the present state of our knowledge, there is no sufficient evidence that intellection is exclusively exe- cuted by any one part of the cerebrum, but probably that all are auxiliary to, and concur in, this great end. Besides intellection, there are two other elasses of vital phenom- ena to which we have referred as being connected with the en- cephalon, viz., voluntary motion and sensation. The former of these has been supposed to be ultimately referrible to the cere- brum, and the latter to the cerebellum. But this may be more satisfactorily shown in investigating the functions of the medulla 166 FUNCTIONS OF RELATION. spinalis and cerebro-spinal nerves. Another feature in the struc- ture and functions of the encephalon, which has been already al- luded to, and which it is indispensable to keep in mind in our physiological and pathological investigations, is the symmetrical character of these organs. Like the other double organs, as we have seen, each half appears to possess, to a certain degree, an independent power of action. They are, however, peculiar in this, that the influence of each hemisphere, instead of extending to the corresponding side of the body, is chiefly confined to the opposite side. The advantages of this arrangement are not obvi- ous, though incontrovertibly established. Hence, it happens that lesion of one side of the encephalon is accompanied by impaired sensation or voluntary motion, or both, on the opposite side. This is, however, generally, not invariably true, sometimes the par- alysis corresponding to the side of the encephalon where the le- sion exists. The offices of the cerebellum have not been ascertained with much precision. One of these functions which has of late excited considerable attention, but of which our knowledge is at present loose and indefinite, is the supposed influence exercised by it over the generative functions. There are sound analogical reasonings and pathological facts which appear to furnish support to this doctrine, to which it will now be proper to refer. In the first place, it has been remarked by phrenologists, by which we mean the followers of Gall, that the development of that part of the cra- nium in which the cerebellum is contained, and, of course, the or- gan itself, indicates, with great uniformity, the erotic disposition of the individual. It is undoubtedly true, that a great expansion of this part of the cranium, accompanied, as it usually is, with corre- sponding thickness of the neck, tends to give a gross and sensual expression to the individual. It is also frequently true, that persons of this conformation are generally distinguished for their robust constitution, and, perhaps, for their inclination to venereal indul- gence, though the latter may be a consequence of the former. The effects of emasculation upon the development of this part of the cra- nium and neck, in the inferior animals, particularly the horse and bull, have also been referred to as furnishing strong proofs of the intimate connexion existing between the cerebellum and the gener- ative organs. The cerebellum rapidly increases from childhood with advancing age, its magnitude, in proportion to the rest of the encephalon, being double at puberty that of the infant. It has also been frequently remarked, that pain in this part often follows excessive indulgence of this passion ; while in the female it is oft- en complained of during menstruation. There have been a number of remarkable cases related by Serres, Larrey, Andral, and others, of persons dying with symp- toms of excitement of the generative organs, satyriasis, nympho- mania, priapism, &c., &c, in whom there was found after death marks of inflammation, or hemorrhage, in the cerebellum, par- ticularly the middle lobe. Some remarkable cases are also rela- CEREBRUM AND CEREBELLUM. 167 ted of wounds of the occiput having been followed by loss of the venereal appetite, and atrophy of the generative organs. Serres has related a number of curious facts of this kind that fell under his observation. In one instance a man was seized with apoplexy during coition. Priapism continued until the ap- proach of death. On examination, there was found hemorrhagic effusion into the substance of the cerebellum at a great number of different points. In another person who had died apoplectic, in whom also priapism constituted a symptom which continued until the approach of death, indications of inflammation, and erosion of the middle lobe of the cerebellum, were found; and a large co- agulum of blood effused into the right lobe of the organ, which had forced its way into the fourth ventricle. This man had sever- al apoplectic paroxysms in the two days which preceded his death, during each of which there was a tense erection of the pe- nis, and in the last an abundant discharge of semen. In a third case, attended with symptoms of satyriasis, ejaculation of the se- men, and tumefaction of all the generative organs, there were found indications of inflammation in both the right and left lobes of the cerebellum, and gangrenous effusion at a number of points in the middle lobe. In a body brought to him from the hospital of the Bicetre, in which there was great tumefaction of the penis and scrotum, he found extensive inflammation of the cerebellum. A girl who had given herself up to the most licentious habits, and who died with violent symptoms of nymphomania, exhibited marks of chronic inflammation and induration of the middle lobe of the cerebellum.* Baron Larrey, in his Clinique Chirurgicale, has recorded also a number of cases having a similar bearing. In some, where shrinking of the occiput occurred, apparently as a consequence of emasculation; and others, where injuries of the cerebellum were alleged to have been followed by atrophy and loss of function of the genital organs. One of the most remarka- ble of these cases is that of a soldier, who was wounded in the back of the head, but got well. When the baron saw him, three months afterward, he states that he was so changed that he did not know him. He had become beardless, and his voice was fem- inine. On examination, he found the genital organs in a state of atrophy, reduced to the size of those of an infant. Some have undertaken to doubt the accuracy of these last statements, though we are not aware of its having been done on sufficient authority. But cases similar to those which we have thus related have been described by some of the highest and most recent authori- ties in the profession. Andral, in his late excellent work, the Pa- thologie Interne, has related several interesting cases corroborative of this reciprocal influence supposed to exist between the cerebel- lum and genital organs, though he is far from giving an unquali- fied assent to this doctrine. Pains of the occiput are common, not only during menstruation, but also frequently arises as a conse- * V. Begin, &c. 168 FUNCTIONS OF RELATION. quence of disordered menstruation. But this, as we shall see hereafter, does not necessarily arise from irritation of the cere- bellum, but sometimes from spinal irritation. M. Andral speaks of a young man who came under his care, who suffered excruci- ating pain in the occiput always after coition. Another had suf- fered for a considerable time from frequent painful priapism, du- ring which he had an acute pain in the occiput. One day M. Andral was sent for in great haste to this last patient, and found him labouring under all the symptoms of acute meningitis, accom- panied with furious delirium, of which he died. Unfortunately, no post mortem examination was made. f But when we deliberately examine the known facts on this sub- ject, they by no means conclusively establish the doctrine that the cerebellum is exclusively, or even chiefly, appropriated to the generative functions. Comparative anatomy is for the most part opposed to it. The male frog is so excited during the season that it will endure the most extensive mutilations without relaxing its em- brace of the female, yet its cerebellum is much smaller proportional- ly than some of the fishes, which have no direct sexual intercourse. One of the strongest arguments in favour of this doctrine is the apparent shrinking and assumed atrophy of the cerebellum in emasculated animals, particularly the stallion and bull. But the recent observations suggested by M. Levret, published in his Comparative Anatomy of the Nervous System, proves that these assumptions are entirely unsupported. The experiments were made by M. Lassaigne on ten stallions, of the ages of from 9 to 17 ; in twelve mares, of from 7 to 16 years ; and twenty one geld- ings, from 7 to 17 years. The weight of the cerebellum, both ab- solute and as compared with that of the cerebrum, was adopted as the standard of comparison. The results of these observations were directly opposed to the statement of the phrenologists. They proved that the proportional size of the cerebellum in geld- ings was decidedly greater, instead of less, than either in entire horses or mares. The following is a comparative statement of the weights: Average. Highest. Lowest. Stallions, 61 65 56 Mares, 61 66 58 Geldings, 70 76 64 These experiments go far to show that, instead of the cerebel- lum being reduced by castration, as asserted by Gall, the reverse is true, and that the cerebrum is more likely to have its compar- ative size diminished by this operation. But if organic lesions of the cerebellum have in some instances been attended by disordered function of the genital organs, as has been now described, yet it must be acknowledged that this is far from being uniformly the case, nor is it by any means certain that they were not mere accidental coincidences. On the contrary, the greatest variety in the symptoms consequent upon acute and chronic inflammation, sanguineous effusion, and injuries of the cer- MEDULLA SPINALIS. 169 ebellum, has been observed. In some cases, hemiplegia, in oth- ers, mere muscular weakness ; again, in some the sensation is dis- ordered or abolished, while the power of voluntary motion con- tinues. Amaurosis has also been frequently observed to occur in children, where dissection has shown tubercles of the cerebellum. There is another circumstance which may be mentioned as hav- ing a bearing upon this point, the reciprocal influence of the cere- bellum and genital organs. It is the change which takes place in the latter on the approach of old age. There is not only impaired function, but even atrophy of these organs, though no correspond- ing change occurs in the cerebellum. The cerebrum sometimes shrinks in old age, but it is remarked that this rarely, if ever, oc- curs in the cerebellum. The following curious case tends still more strongly to create doubts on this point. It is a case related by Dr. Combette, of a girl who lived until she was eleven years of age, in whom the cer- ebellum was found in a state of atrophy. She was melancholy, of limited intelligence, but the other functions were natural.* This girl had been known for several years to indulge in mastur- bation. Andral states that he had been able to collect but twenty cases of tubercle of the cerebellum. Of this number there was but one, a case recorded by M. Montault, in which there were any remarkable symptoms connected with the generative organs. In him the venereal desire is represented to have been excessive.! What adds very much to the difficulty and obscurity of this sub- ject is, that inflammation and congestions of the cerebellum are very often complicated with similar affections of the cerebrum. Thus it becomes extremely difficult to discriminate between the symptoms. In the present state of our knowledge, then, it is doubtful how far the cerebellum exerts a peculiar influence over the functions of the genital organs. It is one of those vexed questions in which the judgment should be kept in abeyance until elucidated by far- ther inquiry. Medulla Spinalis. The functions of the medulla spinalis are intimately connected with those of the cerebrum and cerebellum, yet, like them, its of- fices may in some degree be regarded as independent. Though great light has been thrown on the functions of the spinal chord, especially by the investigations of Sir Charles Bell, and M. Ma- gendie, yet the precise offices of the central nervous masses are far from being clearly defined. The subject is complicated, and is still involved in much obscurity. To render it more intelligible to the student of physiology, we present in the following diagram a delineation of the whole of the cerebro-spinal axis, seen on its an- terior surface, the nerves being divided at a short distance from their origin. * V. Gazette des Hopitaux, 1831. t Pathologie Interne. Y 170 FUNCTIONS OF RELATION. CerebrospinalA,is. a. The brain, b. The anterior obe of 6 the left hemisphere, c. The middle lobe. d. The posterior lobe, nearly concealed 'c by the cerebellum. /. Medulla oblongata. 7 l. Nerves of the first pair, or olfactory. ■de 2. Second pair, or optic. 3. Nerves of - c the third pair, which originate behind the :.u interlacing of the optic nerves in front of ;]l the pons varolii, and above the peduncles e of the brain. 4. Nerves of the fourth pair. 5. Trifacial, or nerves of the fifth pair. 6. Nerves of the sixth pair, lying 25 on the pons varolii. 7. Facial nerves, or nerves of the seventh pair; and acoustic, "f or nerves of the eighth pair. 9. Glosso- pharyngeal, or nerves of the ninth pair. 10. Pneumogastric, or nerves of the tenth pair. 11. Nerves of the eleventh and •33 twelfth pairs. 13. Suboccipital, or nerves of the thirteenth pair. 14, 15, 16. Three first pairs of cervical nerves, g. Cervical nerves, forming the brachial plexus. 25. "h A pair of the dorsal nerves. 33. A pair of ""* the lumbar nerves, h. Lumbar and sac- ral nerves, forming the plexus, from which -jt arises the nerves of the lower extremities. i and j. Termination of the spinal marrow, called the cauda equina, k k. Great sci- atic nerves going to the lower extremi- ties. The following diagram (Fig. 23) represents a vertical section of the cerebrum, cerebellum, and medulla oblongata, with the nerves which arise from the base of the brain and medulla oblongata, and their general distribution. A. Anterior lobe of the cerebrum. B. Median lobe. C. Pos- terior lobe. D. Cerebellum. E. Spinal marrow. /. Section of the corpus callosum. g. The optic lobes. 1. Olfactory nerves. 2. The eye, in which terminates the optic nerve, the root to which may be followed on the sides of the annular protuberance to the optic lobes ; behind, we see the nerve of the third pair. 4. Nerve of the fourth pair, which is distributed, like the preceding, to the muscles of the eye. 5. Superior maxillary branch of the fifth pair. 5. Opthalmic branch of the same pair. 5. Inferior maxil- lary branch of the same nerve. 6. Nerve of the sixth pair, going to the muscles of the eye. 7. Facial nerve. Below the origin of this nerve we see a section of the acoustic. 9. Glosso-pharyn- geal, or nerve of the ninth pair. 10. Pneumogastric. 11. Hy- poglossal, or nerve of the eleventh pair. 12. Spinal, or nerve of the twelfth pair. 14, 15. Cervical nerves. MEDULLA SPINALIS. 171 (Fig. 23.) A Vertical Section of the Encephalon, from Milne Edwards. 7 11 9 10 6 E The brain and medulla spinalis communicate through the me- dium of the medulla oblongata ; hence the importance of a knowl- edge of this part physiologically. The thirty-one pairs of com- pound nerves, that arise from that portion of the spinal marrow contained in the vertebral canal, arise by double roots, presenting, near their origin, a ganglion. (Fig. 24.) A Section of the Medulla Spinalis, to show the Origin of the Compound Nerves. a. Spinal marrow, b. Anterior root of one of the spinal nerves. c. A ganglion situated in the course of this root. d. The pos- terior root of the same nerve, united to the anterior root beyond the ganglion, e. The common trunk, formed by the union of these two roots. /. A small branch anastomosing with the great sympathetic nerve. The medulla spinalis, when removed from its bony case, pre- sents an outline which has been compared to a pillar, of which 172 FUNCTIONS OF RELATION. the medulla oblongata is the capital, and which extends the whole length of the trunk. It is the first part of the encephalon devel- oped in the foetus, and the only portion of the brain indispensable to foetal life and growth, as would appear from the fact that acepha- lous children, in whom all the parts of the cerebrum and cerebellum are wanting, except the medulla oblongata, are often well formed, and even robust at birth; yet they rarely survive for more than a few hours. We also sometimes meet with cases of chronic hydrocephalus, in which there is entire disorganization of the cerebrum and cerebellum, yet the child may support a sort of ve- getative life for years. The importance of the medulla oblongata, as a part of the medulla spinalis, may be inferred, not only from its being always found in acephalous children, but also from the fact that if, in the turtle and some other cold-blooded animals very tenacious of life, the head be cut off, if the decollation be practised below the medulla oblongata, the body dies, and the head continues to live; but if above this part, it is the reverse. M. le Gallois also found that he could cut down the brain until he came to this part without interrupting the respiration; but if it was mutilated, this function ceased. The medulla spinalis is a prolongation of the encephalon, ar- ranged into such a form as to facilitate free and equal communi- cation between the central nervous masses and the remote parts of the body, through the medium of the nerves. According to Sir Charles Bell, it consists of three distinct parts: the anterior fasciculi destined to voluntary motion, the posterior to sensation, and the middle to respiration. Its structure is fibrous, any inter- ruption of the continuity of which is followed by a loss, or other lesion of sensation or voluntary motion, at or below that portion of the body at which the injury occurs. Sensation and voluntary motion are the most widely-extended offices of the cerebro-spinal system. There are forty-three pairs of cerebro-spinal nerves; of these, thirty-one pairs are appropri- ated to common sensation and voluntary motion. The latter, with a single exception, viz., the trigeminus, arise with great reg- ularity in pairs on each side of the medulla spinalis. They are called compound nerves, because they arise by double roots from the anterior and posterior fasciculi of the cord ; they are then uni- ted in one sheath, and, as they retain the original properties of the portions of cord from which they are derived, they are each com- posed of a filament of sensation and voluntary motion. These compound nerves pass out at right angles from the medulla spina- lis, and are distributed to the corresponding portions of the body; the upper cervical to the head and neck, the lower cervical and upper dorsal to the superior extremities and corresponding por- tions of the trunk, and the lower dorsal and lumbar to the inferior portions of the trunk and lower extremities. Another circum- stance in the distribution of the compound nerves, exceedingly in- teresting in a pathological point of view, is their connexion with the great sympathetic nerve. These nerves, as they pass from MEDULLA SPINALIS. 173 the medulla spinalis, run directly to communicate with the sym- pathetic, sending probably filaments to be distributed with it to the corresponding vis«era and parts of the body. As the func- tions or properties of the compound nerves depend upon the medulla spinalis, any lesion of the medulla spinalis itself, or of the nervous filaments at any intermediate point between their origin and periphery, will impair or destroy their function. • Thus, if in- jury of a filament of sensation going to one of the extremities oc- curs, the result may be increased, diminished, modified, or lost sensibility in the part, the power of voluntary motion, remaining unimpaired, and vice versa. The seat, nature, and extent of the lesion, whether it affect a single nervous filament, a considerable trunk, or the medulla spinalis itself, will determine the character of the morbid phenomena that will ensue. Thus there may be numbness, loss of sensation, formication, or neuralgic pain. If there be lesion of the filaments of motion, there will be spasms, convulsive twitchings, muscular weakness, or entire loss of the power of voluntary motion. These lesions of sensibility and vol- untary motion may exist singly or together; they may affect a very limited space, as the tip of the finger, or extend to half the body, or all. Sensation, which may be considered as including the sense of touch, is very widely diffused. It constitutes a most important sentinel in protecting the organization from various noxious influ- ences to which it is exposed. Its distribution over the integu- ment is indispensable to its preservation. We are thus admon- ished not only of injurious variations of temperature, but are also prevented from subjecting any part of this organ to long-contin- ued pressure by remaining long in the same position. In lying, the pressure made by the prominences of the bones become disa- greeable, and we change our posture. We see the importance of this admonition in those cases where there is loss of sensibility, paralytics being exceedingly liable to ulceration, and even gan- grene of the skin, from this cause. Another striking example of this is alluded to by Sir Charles Bell. The cheek derives the power of sensation from the ganglionic, and of voluntary motion from the ganglion/ess portion of the trigeminus. In paralysis of the trigeminus, the tongue still retaining its power of voluntary motion, during mastication the food accumulates between the cheek and jaw of the paralyzed side, and has been known to re- main in this state, without the consciousness of the patient, until putrefaction had taken place. Indeed, the presence and charac- ters of disease are traced chiefly by means of disordered sensa- tions and voluntary motions. In explaining these phenomena, we are, therefore, to keep in mind the origin, structure, functions, and distribution of the nerves of sensation and motion. In most path- ological conditions, this is the only key to a just diagnosis and sound therapeutic treatment. Thus we can understand how lesions of particular portions of the medulla spinalis, by modifying the functions of the compound 174 FUNCTIONS OF RELATION. nerves which pass off at these points, are indicated by disordered sensibility, motion, or other function in the corresponding organs and parts of the body. We also thus see satisfactorily explained, how it'often happens, that when there is a considerable lesion of a portion of the medulla spinalis, not only the functions of the cor- responding parts of the body are affected, but also those parts which are situated below the point at which the lesion or disor- ganization exists. This is, however, a general, not universal law, there being some extraordinary exceptions recorded of the re- verse. M. Velpeau has described some remarkable instances of this. In one case, a young man died, at the age of eighteen years, after protracted sufferings arising from an injury of the occiput. To the last the sensation and voluntary motion remained, so that he could walk about. After death the medulla oblongata was found entirely separated from the medulla spinalis, being only connected by a disorganized gelatinous mass, through which the nervus accessorius and the hypoglossus traversed; but the par vagum and glosso-pharyngeus of the left side were completely severed. Under and concealed by this diseased portion of the medulla spinalis, the tooth-like process of the vertebra dentata was found, pressing upon the diseased portion of brain. In another case, the sensibility and voluntary motion of the lower extremities remained until death, though the bodies of the vertebrae from the tenth dorsal to the sacrum were carious, the spinal column at this part bent to a sharp angle, and the medulla spinalis at this part softened, rotten, and almost destroyed, and several of the com- pound nerves separated from their origin, nearly four inches of the dura mater being wanting at this part. In another case, of nearly three years' standing, the sensibility and voluntary motion remained to the last, though a post mortem examination showed more than four inches of the medulla spinalis wanting, that space being filled with a reddish fluid. Many other remarkable cases are recorded of this kind. One by Dessault, of a complete divis- ion of the cord by a musket-ball, without paralysis. Another, communicated by M. Ferrein, of a soldier, from whose spine the point of a sword was extracted, which had traversed the vertebral canal and spinal marrow without occasioning paralysis, the pa- tient having marched eighty leagues after the accident, but died almost immediately after the extraction of the fragment. These are, however, extraordinary exceptions to a general rule, consid- erable lesions of the medulla spinalis being generally attended with paralysis of the parts situated below the lesion. M. Begin doubts the accuracy of these statements, but it would seem without sufficient authority. Though contrary to our general experience, they are not without analogy. Our knowledge of the mode in which innervation takes place is very imperfect, and many of the facts, therefore, connected with it are very obscure and in- explicable. We have seen what extreme disorganization of the cerebrum may take place, and yet the intellection continue normal. * See Physiologie Pathologique, t. i., p. 243. MEDULLA SPINALIS. 175 In the experiments of Dr. Wilson Philip on the effects of the di- vision of the pneumogastric nerve, he found that the digestion of the rabbit did riot cease entirely if the divided ends of the nerve were allowed to remain in contact. Cerebro-spinal System of Nerves. If we consider the cerebro-spinal axis the centre of the nervous system, and the cerebro-spinal nerves the media between it and the remote parts of the body, through the agency of which sensa- tion and voluntary motion are executed, the inquiry naturally ari- ses as to the action of these agents, the nerves. Notwithstand- ing the intimate connexion between sensation and voluntary mo- tion, yet, viewed with respect to the encephalon, as the sensorium commune, their relations are widely different. The sensations obviously pass from the periphery of the nerves to the encepha- lon ; the influence which produces voluntary motion, on the con- trary, in an opposite direction. If we expose a sentient nerve, and irritate or cut it, the influence is propagated to the centre, and hence pain. But if it be a motor nerve, spasm or loss of motion will ensue in the part to which the nerve is distributed, but not pain. It would appear that the cerebro-spinal system acts in a circle. The nerves would seem to be so constituted that they can transmit their peculiar influence only in one direction. The sentient nerves receive impressions from without, which pass through them to the sensorium; the motor nerves transmit the mandates of the will, consequent upon these sensations. The fol- lowing experiments, by Mr. Mayo, beautifully illustrate this circu- lation of nervous power. The iris derives its motor power from the third pair of nerves. It is well known that the use of this movable veil is to admit to the interior of the globe of the eye the quantity of light most favourable to the action of the retina. Its action is, therefore, intimately associated with the optic nerve. Mr. Mayo found that, on dividing the optic nerve, the motions of the iris ceased ; but that, if he irritated that extremity of the di- vided nerve next to the brain, the iris again contracted. But no influence could be produced upon this muscle by irritating that extremity of the divided optic nerve attached to the globe of the eye. The plain interpretation of these phenomena is, that in the first experiment, an impression being communicated through a sen- tient nerve, the optic, to the brain, a corresponding influence was transmitted from the encephalon towards the circumference through the motor nerve, and hence the motion of the iris. This was confirmed by the effects of dividing the third pair, after which no motion of the iris could be produced by irritating either extrem- ity of the divided optic nerve. But though the division of the trunk of a nerve, by interrupting this circle, and cutting off the communication between the remote part and the sensorium, deprives it of sensation or motion for the time, yet this loss of power is not necessarily final. As proofs of this, we may refer to the experiments of Dr. Wilson Philip on the 176 ruNOTIONS OF RELATION. division of the pneumogastric nerve in the rabbit, where the di- vided ends of the nerve were allowed to remain in contact. Cic- atrization also sometimes takes place, and the function of the nerve is permanently restored. This has been so frequently ob- served by surgeons, after dividing the trigeminus in tic douloreux, and in other neuralgic affections, that they often remove a portion of the nerve to prevent a return of the disease. It has been ques- tioned whether this restoration of the functions of the nerve is at- tributable altogether to the cicatrization, or whether the nervous influence is derived, to the parts situated beyond the point of divis- ion, from other nervous trunks in the neighbourhood. There are some remarkable and well-attested facts which favour the latter opinion. Thus, it is observed, that if the trunk of a nerve going to a part which is exclusively supplied by that nerve be divided, the function is never restored, e. g., a division of the circumflex nerve, which alone supplies the deltoid, is observed to be follow- ed by an incurable paralysis of that muscle. A similar result oc- curs in the leg and foot, on the division of the great sciatic nerve. —(Begin, t. i., p. 190.) It is not improbably owing to these rela- tions that, after rheumatic affections of the deltoid, this muscle is so slow in recovering its power, and, indeed, often remains per- manently paralyzed. This affords an explanation of one of the uses of the numerous interlacings and communications in the course and distribution of the nerves. Inflammations and other affections of the tissues necessarily in- volve the periphery of the nerves, the minute filaments of which constitute one of their organic elements, and modify their func- tions. In every morbid condition of a part, there is, therefore, some change in its sensations, motions, and other functions. In the more common and active forms of disease, pain in the part is one of the most uniform symptoms of lesion in all the tissues. In our examination of those organs, which can only be approached by the taxis, in order to ascertain their pathological condition, our diagnosis, for the most part, is guided by the state of the sensa- tions and functions of the part. If pain, morbid sensibility, and deranged function exist, we generally infer there is local inflam- mation. We so frequently find the morbid sensation indicate the seat of the disease, that, at last, we are apt to regard it as a cer- tain guide. But, though in many cases the morbid sensation tru- ly indicates the sentient extremities of the nerves as being the seat of the disease, yet it by no means uniformly holds good. In some cases, the pain or morbid sensation exists at the sentient extrem- ity of the nerve, when the true seat of the disease is either in one of the central nervous masses from which the nerve is derived, or at some remote part of its trunk. A morbid condition of that portion of the encephalon from which a nerve is derived, or an injury inflicted upon the trunk at some intermediate point in its course, is not unfrequently indicated alone by pain or other mor- bid sensation in that texture to which the sentient extremity of the nerve is distributed. The inaccuracy of our sensations as MEDULLA SPINALIS. 177 guides in this respect is strikingly shown in what frequently oc- curs after the amputation of a limb. In these cases, it is not un- common for the patient to complain of pain in the severed ex- tremity long after the operation. He sometimes feels as If its po- sition were painful, and unconsciously makes an effort to change it. In affections of the medulla spinalis, or of the compound nerves at their origin, the patient often makes no reference to the seat of the disease, but complains of pains, spasmodic twitching, loss of sensation or motion, &c, in the parts to which the nerves are distributed. Hence has often arisen the greatest obscurity in the diagnosis, pathology, and treatment of these diseases. The success of our practice, for the most part, depends on the correctness of our diagnosis, and addressing our remedies to the seat of the disease. If the morbid condition be at the encephalic extremity of the nerve, and the remedies applied to its periphery, our therapeutic efforts will be exceedingly apt to fail. Thus, neuralgic affections of the eye, teeth, and face often exist together, which can only be relieved by ascertaining the original seat of the disease, and ad- dressing our remedies to it.—(See Marshall Hall on the Reflex Functions of the Medulla Oblongata, p. 40.) The morbid sensi- bility of the part is, in some instances, a sufficient guide, but m others it is entirely inadequate. In that extensive class of dis- eases called the neuroses, including angina pectoris, tetanus, hydrophobia, epilepsy, hysteria, chorea Sancti Viti, &c, until very recently, all the reasonings of pathology were set at defiance; mere empiricism being the only guide in their diagnosis and ther- apeutic treatment. It is not pretended that this obscure depart- ment of pathology has been stripped of all its difficulties, but great light has certainly been thrown upon it by modern investi- gations of the functions of the nervous system. 3 In the neuroses, there are a great .number of anomalous symp- toms quite inexplicable, according to the theoretical opinions for- merly entertained on this subject. The most common and promi- nent are characterized by morbid sensations in parts which are ob- viously not the true seats of the disease. In the globus hystericus, the morbid sensation points to the stomach; the aura epileptica, to one of the limbs; the pain under the left mamma in chronic hysteria, to the lungs, &c, as being the seats of disease. But it is now admits ted that, in a great majority of cases, these indications are false. Though the more remarkable sensations exist at the periphery of the nerves, where they are lost in the textures of the organs, yet it is apparent that the irritation is generated about the origin of the nerves, or perhaps the encephalon itself. When inflammation occurs in a texture, it not unfrequently happens that the irritation is propagated for a considerable dis- tance along the trunks of the nerves distributed to the part. Thus, in chronic inflammation, thickening and change of structure are some- times induced in the trunk of the nerve, attended with severe neuralgic pains and spasms about the parts to which the nerve is 178 FUNCTIONS OF RELATION. distributed. Similar consequences also often arise from punc- tured, contused, and lacerated wounds of the trunks of the nerves. In other instances, the morbid effects are propagated towards the origin of the nerve, sometimes even involving the encephalon, in- ducing abscesses of the brain, epilepsy, convulsions, tetanus, &c. Again: In health, it appears that impressions made on the sen- tient extremities of the nerves are propagated towards the centre, and are exactly represented to the sensorium. But lesion of the nerves of sensation, either at their encephalic or sentient extrem- ity, or at any intermediate point, will derange the accuracy of the impression. The circumstances will often enable.us to de- termine with considerable certainty the seat of the lesion. When we see, e. g., a black spot, looking like an insect flitting before the eye, in whatever direction the organ is moved, the health in other respects being little disturbed, we infer that it is caused by the imperfect innervation of some spot upon the retina. But when the encephalic extremity of the nerve, perhaps the enceph- alon itself, is the seat of disease, though the impression made upon the organ of sense be accurate, yet the image presented to the mind is false or distorted. It would appear probable that the phenomena observed in delirium are produced in this way. Though the eyes and the ears may appear to be perfect in their organization, and prompt in their action, yet things are no longer perceived as they are actually. The patient sees objects which do not exist, and hears sounds that are not made, and holds con- versation with imaginary beings. In excited states of the brain, as in the earlier stages of acute diseases, there is coherency of thought, and the perceptions, though exaggerated or false, at least possess some verisimilitude. But where the vital powers are prostrate, as towards the close of violent diseases, not only are the perceptions false, but the thoughts incoherent and wan- dering, constituting what is called low, muttering delirium. The mind possesses a certain influence over the perceptions; even in health, our thoughts impart a character to the objects we are contemplating. With a little effort, especially if objects be im- perfectly seen, we can thus distort them into innumerable fanci- ful forms, giving to them the shape and hue of our own thoughts. In certain morbid conditions, where the intellection could scarce- ly be said to be disturbed, and where the organs of sense exhib- ited no outward evidence of disease, individuals have witnessed the most extraordinary visions. In some instances, these spectral illusions have been seen for a length of time, and examined with a minuteness of detail, that it required no ordinary force of intel- lect to recognise the phenomena as imaginary, the result of a morbid condition of the organism. We thus perceive that delir- ium is generally an unfavourable symptom, as it indicates dis- ease and loss of power in the centre of the nervous system. Action of the Cerebro-Spinal System of Nerves. It is a general law of the nervous system, that one nerve con- OF MUSCULAR CONTRACTION AND THE VOICE. 179 fers but one property upon the part to which it is sent, according to the portion of the encephalon from which it is derived. In the trunk and extremities, sensation and voluntary motion are the principal offices; the nerves sent to these parts are, therefore, few in number, and simple in their distribution. The face pre- sents a striking contrast in this respect; in this space a great number of important organs are assembled, and distinct acts exe- cuted ; not only common sensation and voluntary motion to be per- formed, as in other parts, but various sensations pertaining to the organs of the senses, and both voluntary and involuntary motions. Inconceivably delicate and complicated muscular motions are ex- ecuted here with extreme rapidity, and in exact unison. It is suf- ficient to allude to a few of these functions, viz., vision, audition, smell, taste, respiration, deglutition, the voice, expression, &c, to illustrate this. Hence the great number and complexity in the arrangements of the cerebro-spinal nerves sent to this part, which renders their study extremely obscure and difficult. This obscu- rity is, however, diminished by the fact that whereas, in the trunk and extremities, sensitive and motor filaments are bound in the same sheath, and sent to remote parts like one nerve, in the face each nerve generally runs separate, from its origin to its distri- bution. It may be inquired, Why are the voluntary muscles also sup- plied with sentient nerves ? It may be replied, that the muscles are not exclusively destined to motion, but that their action is also governed by the resistance which they are intended to overcome, and that this resistance can only be known by the agency of the sentient nerves. Thus, in cases of anasthesia, in which the sen- tient filaments are paralyzed, while the motor nerves retain their power, the utility of the latter is greatly impaired. We could not retain a lifted weight, or balance the body in standing or walking, were not the action of the muscles regulated by the sentient nerves. The sensibility of the muscles differs from that of the skin probably rather in kind than in degree. The offices of the integument demand the power of perceiving promptly the action of external agents, it being the sentinel by which the organism is guarded from noxious influences from without. Hence it is high- ly susceptible to that modification of sensibility which is. manifest- ed by pain.—Ed.~\ CHAPTER XL OF MUSCULAR CONTRACTION AND THE VOICE. The functions which we have now examined depend entirely on the faculty of perception. It is by this faculty that we arrive at a knowledge of the objects which surround us, and of ourselves. 180 FUNCTIONS OF RELATION. To terminate the history of the functions of relation, it only re- mains for us to speak of those functions by means of which we act upon foreign bodies, impress upon them the changes which we judge necessary, and express our sentiments and ideas to those by whom we are surrounded. These functions are but different shades of the same phenomenon, muscular contraction. So that the faculty of perception on the one side, and muscular contrac- tion on the other, constitute really all our life of relation. We shall first define muscular contraction in general; after which we shall treat of its principal results, voice and motion. Muscular contractility, which has also been called animal and voluntary contractility, is not a simple vital property, at least in the sense which we attach to this word. It results from the success- ive or simultaneous action of several organs, and ought, therefore, to be viewed as one of the natural powers. Apparatus of Muscular Contraction. The organs which concur in muscular contraction are the brain, nerves, and muscles. Of the Parts of the Encephalon which appear more particularly destined to Motion. Certain parts of the cerebro-spinal' system appear more par- ticularly destined to motion. In proceeding from the anterior to the posterior part, there are the corpora striata, the inferior por- tion of the optic thalami, the crura cerebri, the pons varolii, the peduncles of the cerebellum, the lateral portions of the medulla oblongata, and the anterior fasciculi of the medulla spinalis. We shall soon cite facts on which we rely to show that these parts have a remarkable influence in the production of muscular con- traction. Nerves of Motion. Anatomists have long sought to distinguish the nerves which confer sensibility from those which are specially destined to mo- tion. They have been induced to pursue this investigation with the more zeal, as we daily see these two phenomena isolated by disease. We frequently see instances where a part will lose its sensibility and preserve its power of motion, and the reverse. I have had the happiness to establish this distinction by experiment, and it is generally known, since the publication of my work, that the anterior roots of the spinal nerves are the essential nerves of motion to all parts of the trunk and the extremities. With respect to the face, it is evident, from one of the most beautiful experiments of Sir Charles Bell, that the nerve of the seventh pair is particularly the organ which imparts the power of motion to the eyelids, cheeks, and lips. Experiment has also taught us that the hypoglossal nerve and the glosso-pharyngeus are more particularly destined to the motions of the tongue; that the muscular portion of the fifth pair directs those of the jaw; and OF MUSCULAR CONTRACTION AND THE VOICE. 181 that the third, fourth, and sixth pairs concur more especially in the motions of the iris and the globe of the eye. We shall return to the consideration of these new facts under the head of partial movements. I have given in another place the experimental proof that the eighth pair directs the motions of the glottis, as we shall see in the article Voice. Messrs. Prevost and Dumas have been recently occupied in ex- amining the structure of the nerves that are distributed to the muscles, and their manner of distribution in the midst of the mus- cular fibres. A great number of observations made with the mi- croscope on the nerves of the rabbit, the Guinea pig, and the frog have taught them, 1st. That, when magnified ten or fifteen times, the nerves present on their surface alternately white and dark bands, which strikingly resemble a spiral line under the cellular envelope. But this appearance is illusory; it depends simply on a small fold of the envelope, which loses its transparency in some points, and preserves it in others. The proof of this is, that if we draw slightly the nervous filament, while placed under the lens, it disappears. If we take a nerve, and after having divided it longitudinally, we place it under water, we shall find that it is composed of a great number of small filaments, parallel to each other, and of equal size. These filaments are flat, and composed of four ele- mentary fibres, arranged nearly in the same plane. These fibres are composed of a series of globules. (See plate, t. iii. of my Journal de Physiologie). Messrs. Prevost and Dumas have com- puted that 16,000 of these fibres may be contained in a cylindri- cal nerve of a millimetre in diameter, as, for example, the crural nerve of a frog. Of the Muscles. All the muscles, taken collectively, are called the muscular system. The form and disposition of the muscles vary infinitely. Muscles are formed by the union of a certain number of muscu- lar fasciculi, which are again composed of still smaller bundles; these, again, are formed of fasciculi of a smaller volume ; and thus, by excessive subdivision, we get a fibre extremely small, and which we can no farther divide, but which might probably be farther divided if our senses and means of division were more per- fect. This fibre, which is indivisible by us, is called the muscular fibre. It is formed by a series of globules, which are kept in a right line by amorphous matter. It is longer or shorter, accord- ing to the muscles of which it constitutes a part; almost always straight, it does not divide, nor is it confounded with other fibres of the same kind ; it is enveloped in a cellular tissue, extremely delicate; it is soft and easily torn in the dead body, but, on the contrary, in the living body it exhibits a resistance, in proportion to its volume, which is surprising; it is essentially composed of fibrine and osmazome; it receives much blood, and at least one nervous filament. Some anatomists have pretended to explain 182 FUNCTIONS OF RELATION. how the bloodvessels and nerves act when they arrive in the tis- sue of the muscular fibres, but nothing satisfactory has been ad- vanced upon this point. The researches on this subject on which we can place the most reliance are those of Messrs. Prevost and Dumas. These learned naturalists have followed with the microscope the distri- bution of the nervous fibres, and they assure us that they are not confounded or gradually blended with the muscles, but that they form a network (un anse), which extends from one nerve to an- other, so as to return back towards the encephalon, after having traversed the muscle. According to the same authors, each ner- vous filament has one extremity at the anterior fasciculus of the medulla spinalis, that it descends towards the muscle, constituting a part of a nervous trunk, and after traversing one or more mus- cular fibres, it then passes back, and is attached to the posterior fasciculus of the medulla spinalis. Each muscular fibre is attached, at its extremities, by fibrous prolongations (tendons or aponeuroses), which are the conductors of its force when it contracts itself. Muscular contraction, as it exists in the ordinary state of life, supposes a free and easy action of the brain, and the nerves which are sent to the muscles, and of the muscles themselves. Each of these organs must receive arterial blood, and the venous blood not be permitted to remain in its tissue for too great a length of time ; if either of these condi- tions be wanting, muscular contraction becomes either imprac- ticable, perverted, or very weak. Phenomena of Muscular Contraction. When examined with a weak magnifying glass, the muscular fibres which form a muscle are parallel and straight while in a state of repose, but much inclined to change their position. If by any cause the muscle contracts, there is immediately apparent in the muscular fibres a very remarkable phenomenon, which had been only vaguely noticed before the time of Messrs. Prevost and Dumas. The fibres become bent into a zigzag, and present a great number of angular undulations, regularly opposite to each other. If the cause that induced the contractions suddenly ceases, the parallelism of the fibres is restored. In repeating this experiment, we cannot fail to observe that the flexions of each fibre take place at certain determinate points, and never at any others. The strongest contractions do not cause an- gles of more than fifty degrees. It is an interesting fact observed by Messrs. Prevost and Dumas, that the nervous filaments which traverse the muscular fibres pass precisely at those points where the angles of flexion are produced, and in a direction perpendicu- lar to the fibres. The same authors think they have proved, by precise observa- tions, that the contracted, or, rather, angular muscular fibre, is not shortened. Thus, during contraction, the extremities of the fibre approach each other, but that the fibre itself loses nothing in OF MUSCULAR CONTRACTION. 183 its length. They have arrived at this result either by measuring directly the contracted muscular fibre, or by calculating the an- gles produced. It has long remained doubtful whether the muscles in-mass, in a state of contraction, are increased or diminished in volume. Borelli alleged that they increase ; Glisson the reverse, which he maintained by an experiment. He plunged his arm into a vessel filled with water, and thought he could perceive a diminution of the level of the liquid at the moment the muscles were contracted. This experiment was cautiously repeated by M. Carlisle, with an opposite result. But it is evident that this mode of experimenting does not admit of the necessary precision, inasmuch as no allow- ance is made for the changes which may take place in the skin and cellular tissue. M.'Barzoletti has made an experiment on this subject which is quite conclusive. He suspended in a bottle the posterior half of a frog. He then filled it with water and closed it up, a gradua- ted tube passing through the cork. He then caused the muscles to contract by means of galvanism, but he could not perceive that it had any influence in changing the level of the fluid in the tube. Thus it is evident that the volume of the muscles is not changed by contraction. [The following figure, from Miiller, represents the zigzag inflex- ions of the muscular fibre described by MM. Prevost and Dumas. (Fig. 25.) Zigzag Inflections of Muscular Fibre. They regard each muscular fibre as consisting of a number of short lines, A, B, C, D, and suppose that the shortening of the muscle during its contraction is due to the above-described angu- lar inflexions of the fibres. But Miiller and other accurate ob- servers have questioned whether this is the sole or even essential cause of the shortening of muscles. Professor Owen and Dr. A. Thompson allege that this zigzag arrangement of the fibres does not occur until the contraction has ceased. According to Miiller, there are two forms of primitive muscu- 184 FUNCTIONS OF RELATION. lar fibrils : 1st, simple uniform filaments ; 2d, those having a var- icose or beaded structure. 1st. Those with simple primitive fibres, and destitute of trans- verse striae, compose the muscular coat of the intestines. Schwann could not detect transverse striae either in the human uterus, or that of the rabbit, or the urinary bladder. The second class of muscles, the primitive fibres of which present a beaded structure, and which have cross markings, have been much more carefully examined than the first. When viewed with the microscope, the beading or cross marking is seen distinctly; they are remarkable for the rapidity and strength of their contractions. This second class includes generally all the muscles of both voluntary and involuntary motion, which are re- markable for their deep red colour (Miiller), though they are not all of this colour ; they are also distinguished for their strength and the rapidity of their contractions. (Fig. 26.) Muscles with Beaded Filaments. Figure 26, taken from Miiller, represents a portion of a broken muscular fibre of animal life, magnified about seven hundred di- ameters, showing the apparently beaded form of the filaments and the production of the transverse striae by the transverse parallel opposition of the beads of the filaments. The transverse striae of the primitive fasciculi, when examined by the microscope, are seen to follow each other very closely, and are quite parallel.—(Muller). The beaded enlargements of the dif- ferent fibrillae appear to have a close adhesion to each other; so that we may consider the fibre as not only made up of longitudi- nal filaments, but of disks (Carpenter), formed by the lateral ad- hesion of the beads, and connected together by their intervening narrow bands. The following figure (No. 27) represents organic muscular fibres, magnified three hundred diameters, showing their flattened form. Most frequently, as at A, the fibres present, at successive points, transparent bodies of various forms, of which the majority are con- tained within the substance of the fibres, and are probably the nu- clei of the primary cells that have coalesced to form them. In some fibres these bodies are not seen, having in all probability been absorbed (Muller), as at B. MUSCULAR CONTRACTION. (Fig. 27.) Organic Muscular Fibres. The following is a representation, after Bowman, of a portion of human muscular fibre, separating into disks by cleavage of the transverse striae. It would appear from the recent observations and experiments of Mr. Bowman, that in a state of contraction there is an approx- imation of the transverse striae, and a general shortening of the fibre, and that its diameter is at the same time increased; but that it is never thrown out of the straight line, except when it has ceased to contract, and its two extremities are still held in prox- .. nity by the contraction of the other fibres. He states that the whole process may be distinctly seen under the microscope in a single fibre isolated from the rest; for this he recommends fibres from the crab and the lobster. The contraction commences usu- ally at the extremities of the fibre, but it frequently occurs also at one or more intermediate points. The first appearance is a spot more opaque than the rest, caused by approximation of the transverse striae, and the shading caused by the approximation of a few segments of some of the fibrillae. This shading, caused by the approximation of the transverse striae, increases in intensity, until it extends through the whole diameter of the fibre. The striae are found to be two, three, and even four times more nu- Aa 186 FUNCTIONS OF RELATION. merous in the contracted than in the uncontracted portion, and proportionally narrower, and more delicate. The line of demar- cation between the contracted and uncontracted portion is well defined, fresh striae being, as it were, absorbed from the latter into the former as the process goes on. The contracted part augments in thickness as the process goes on, but not in a degree proportioned to the diminished length; so that the solid parts lie in a smaller compass than before, the fluid which previously in- tervened between them being pressed out into bullae under the sarcolemma. This appearance is illustrated, after Bowman, in the following figure of the muscular fibre of the Dysticus, contracted in the cen- tre ; the striae approximated, the breadth of the fibre increased, and the sarcolemma raised in bullae on its surface. (Fig. 29.) The force with which the elements of the fibre thus tend to ap- proximate is evidently considerable; for if the two extremities be held apart, the fibre is not unfrequently ruptured. This corre- sponds with an appearance often observed in the muscles of per- sons who die of tetanus. In the ruptured fibres of those muscles which had been the subject of the spasmodic action, the striss have been observed to approximate so closely as to be scarcely distinguishable. Many facts appear to indicate that, when a muscle is even in vigorous action, all its fibres do not contract at the same moment, but that there is a continual interchange, by which the tension is effected, some relaxing while others are shortening. When the ear is applied to a muscle in powerful action, an exceedingly rapid, faint, silvery vibration is heard, which seems to be attribu- table to this constant movement in its substance. On examining a muscle in this state, some fasciculi present a zigzag arrange- ment, while others will be seen to be quite straight, and in a state of contraction. From this it would appear that the former arises from fasciculi that have either not entered into contraction, or have relaxed after being in this state, but of which the extremities are still approximated by the action of the contracting fibres. Though, as will appear from what has been said, we know very little of the mechanism of muscular contraction, yet, from the fact that a single muscular fibre, isolated from all other tissues, can pass into a state of complete contraction when subjected to cer- tain stimuli, the important inference may be drawn that contrac- tility is a property inherent in this tissue, and not necessarily de- pendant upon nervous agency, though usually called into action by it, in the living body. MUSCULAR CONTRACTION. 187 Muscles may be thrown into contraction, so long as they pre- serve their vitality, by various chemical and mechanical agents, as cold, heat, electricity, &c. They do not lose their vitality im- mediately with the cessation of the circulation and the occurrence of apparent death. This property lingers longer in some animals and in certain tissues than in others. It is retained much longer in cold-blooded animals than in the vertebrata. It appears, from the experiments of Nysten on the bodies of criminals executed in good health, that in the human subject, the irritability of the mus- cular fibre ceases in the different structures in the following or- der : The left ventricle of the heart, intestinal canal, urinary blad- der, right ventricle of the heart, oesophagus, muscles of animal life ; lastly, the auricles of the heart, especially the right. In the first, it disappears in from forty-five to fifty-five minutes; the last, the right auricle of the heart, has been known to contract, under the influence of galvanism, sixteen and a half hours after death. The muscles of young animals retain their irritability longer than those of adults. Muscular contractility is weakened or destroyed by many substances, especially those which have a sedative or narcotic effect. A watery solution of opium, applied to the mus- cles or injected into the veins, exerts a powerful effect in this re- spect. The same effect is produced by venous blood, charged with carbonic acid and deficient in oxygen, as occurs in those who have died from gradual, and, therefore, prolonged asphyxia; the same influence appears in the consequences of morbus coruleus, in which the patient is incapable of much muscular exertion. It appears to be a general law of muscular contraction that it shall alternate with relaxation at no long interval. This remark equally applies to the muscles of animal and organic life. The contractile power of muscles, especially those of animal life, is developed by exercise and weakened by inaction, the nutritive process being increased by the former and lessened by the latter. This is shown by the muscular development of the arms of the blacksmith, and that of the lower extremities in the opera-dancer. When the muscles are long disused, not only is their bulk dimin- ished, but the muscular fibre sometimes disappears and degener- ates into fat, mingled with the fibrous tissue. The motor nerves cannot be said to terminate in the muscles, in the sense in which this expression is ordinarily used, i. e., to be lost in their structure in minute filaments. The trunks of the nerves form a sort of net- work in the substance of the muscles, the fibres forming loops, as may be seen in Fig. 30, after Burdach, on the following page. The nature of the stimulus communicated by the nerves, and the mode of its communication, are at present mere matters of conjecture. Some similarity has been supposed to exist between the voluntary action of the muscles and that excited by galvan- ism ; but these agencies are obviously merely analogous, not iden- tical : other agents, both physical and chemical, produce the same effects.* * Carpenter. 188 FUNCTIONS OF RELATION. (Fig. 30.) Loops of Nervous Fibres in Muscles. The rigor mortis, or stiffening of the body after death, is evi- dently a phenomenon connected with muscular contractility. This almost invariably occurs, though sometimes so slight and evanescent as to escape observation. It varies in the degree, the period at which it takes place, and its duration, very much, ac- cording to the vital condition at the time of death. In protracted, wasting chronic diseases, and those attended with great exhaus-. tion of vital energy, as typhoid fever, the rigidity occurs early, sometimes in fifteen or twenty minutes, and soon passes by. This remark also applies to young children and old persons. On the contrary, where the death has been sudden and violent, as from certain poisons, asphyxia, blows upon the stomach, lightning, &c, the rigidity is often protracted and slight, and sometimes does not occur at all. This rigor mortis is evidently not dependant upon temperature, as some have supposed, as it occurs in cold-blooded animals, and often in warm-blooded, even before there is any es- sential loss of heat. The muscular contraction appears to be de- pendant upon nervous agency, sometimes rendering the muscles prominent, as in voluntary contraction. The passing away of this state is soon succeeded by decomposition. There is a re- semblance between this state and the coagulation of the blood, though this is rather analogical than identical; like it, it is the last vital phenomenon connected with muscular contractility. This phenomenon sometimes becomes important in settling questions connected with juridical medicine.*] When a muscle contracts, its fibres grow shorter and harder more or less suddenly, without any oscillation or preparatory hesitation; they immediately acquire such a degree of elasti- city that they become susceptible of vibrations, or of producing sounds. The colour of the muscle does not appear to change at the moment it contracts, but it has a tendency to displace itself, which is counteracted by the aponeurosis. All the sensible phe- nomena of muscular contraction take place in the muscles thenv seives, but it is not the less certain thafr these depend upon the> * Applications of Muscular Power, Carpenter, p. 314, sections 395-6. MUSCULAR CONTRACTION. 189 action of the brain and nerves. Compress the brain of an animal, and it loses the power of contracting its muscles. Cut the nerves which are distributed to a muscle, and it becomes paralyzed. We are completely ignorant of the changes that take place in the muscular tissue during contraction. In this respect, muscular contractions cannot be separated from other vital actions, of which we can give no explanation; not but that there have been many attempts to explain, not only the action of the muscles, but also that of the nerves, and even of the brain, in muscular con- traction ; but there is no hypothesis which has yet been proposed that can be considered at all satisfactory.* Instead of consuming our time in such speculations, which it is always easy both to invent and refute, and which should long since have been banished from physiology, we may much more profitably employ ourselves in investigating muscular contraction as it relates, 1st, to its intensity; 2d, its duration; 3d,its rapidity; 4th, its extent. The degree of force with which the muscular fibres shorten themselves is generally regulated by the action of the brain. It is, in general, submissive to the will, varying in degree in each individual. A particular organization of the muscles is favoura- ble to the intensity of its contractions ; this exists when the fibres are voluminous, firm, of a deep red colour, and presenting trans- verse striae. With an equal effort of the Will, they produce great- ' er effects than those muscles, the fibres of which are small, smooth, and of a light colour. Nevertheless, when muscles, the fibres of which are of this last description, are placed strongly under the influence of the will, the intensity of the contraction may be very great; so that cerebral influence, and the disposition of the mus- cular tissue, are the two elementary principles on which the in- tensity of muscular contraction depends. It is rare that we find in the same individual very energetic cerebral action, united with a disposition of the muscular fibres, favourable to intensity of contractions ; it almost always happens that these two principles are opposite to each other. When they happen to be united, they produce astonishing effects. This was probably the case with the athleti of antiquity, and is sometimes observed in the jugglers of the present day. By the influence of the action of the brain alone, muscular power may be exerted to an extraordinary degree. We know very well the astonishing strength of some men in anger, that of maniacs, and of persons in convulsions, &c. This is, in some degree, dependant upon the will, but it cannot be prolonged beyond a certain period, which varies in different individuals. After'this, a sense of fatigue is induced, slight at first but which, at last, increases to such an extent that the mus- cle refuses to contract. The promptitude with which this sensa- * I do not even except the electrical fluid, considered by some as having a certain in- fluence in this phenomenon. It appears, from the ingenious experiments of M. Perron, that no trace of electricity is developed during muscular contraction. 190 FUNCTIONS OF RELATION. tion of fatigue is induced, is in proportion to the intensity of the contraction and the weakness of the individual. To obviate this inconvenience, the different motions of the body are so calculated that the muscles act successively; the contraction of each does not, therefore, continue long. We can thus explain why we do not remain long in the same position; why an attitude, which requires the strong and continued contraction of a small number of muscles, cannot be continued long. The sense of fatigue which follows muscular contraction is dissipated by a state of re- pose, after which the muscle recovers its power of contraction. To a certain extent, rapidity of contractions depends on cer- ebral influence. This is proved by our ordinary movements, but it also sometimes depends upon habit. Observe, for example, what a difference exists as relates to rapidity of muscular con- tractions, between a man who for the first time puts his hands upon the keys of a piano, and the same individual after he has been in the habit of practising for several years ! We observe a very remarkable difference between individuals as respects quick- ness of contraction, both in the common movements and in those which require an appropriate exercise. This is directed by the will, but it must necessarily vary with the length of the fibres, for long fibres must have a more consid- erable extent of contraction than those which are shorter. From what has been said, we perceive that, in general, the will has a great influence upon the contraction of muscles. But this is not indispensable. In a great number of instances, these mo- tions are executed, not only without its participation, but in oppo- sition to it. We find many remarkable examples of this in the effects of habit, passions, and diseases. We must not confound muscular contraction, such as we have now described it, with the modification it undergoes in certain diseases, such as convulsions, spasms, tetanus, wounds of the brain, &c. We must, likewise, take care not to confound that contraction of which we are now speaking with the phenomena which the muscles present for some time after death. Without doubt, these phenomena are curious, and worthy of examination, but they certainly do not merit the importance which has been attached to them by Haller and his disciples, especially as it is not proper to unite them, under the name of irritability, with the other modes of contraction which are observed in the animal economy, and particularly with that of muscular contraction. Modification of Muscular Contraction by Age. It is only at the commencement of the second month that we can distinguish the muscles from the gelatinous mass which con- stitutes the embryo. At this period they do not present any of those characters by which they are distinguished in the adult. They are then of a pale gray colour, slightly tinged with red, and receive but a small quantity of blood,* comparatively speaking. They increase and develop themselves with the progress of its OF THE VOICE. 191 growth, though, even at the period of birth, they are small, flac- cid, and indistinct. We must except, however, those which as- sist in digestion and respiration, which are developed in a remark- able manner. During infancy and youth, the nutrition of the muscles becomes increased, and they grow, particularly in length. This is the reason of the slenderness and agreeable rotundity which we ob- serve in the forms of children and young persons. When a per- son arrives at the adult age, the form undergoes a total change; the muscles increase, and project strongly against the skin; the intervals which separate them being no longer filled with fat, pro- jections and depressions are formed, which give to the body an entirely different aspect from that of childhood. At this age, the muscles assume a greater degree of consistence, the colour be- comes of a deeper red, and even the chemical characters are modified. We learn from daily experiments that, when the flesh of young animals is boiled, the flavour, colour, and consistence of the broth differ very much from that of an adult animal. It ap- pears that the muscles of adult animals contain more fibrine, os- mazome, and the colouring matter of the blood; of consequence, more iron. The nutrition of the muscles diminishes sensibly in old age; they diminish in volume, grow pale, and become flaccid and un- steady, especially in the extremities ; the contractility of the tissue is weakened, the fibre becomes coriaceous, and is torn with diffi- culty. The preparation of muscular flesh is also very different in our kitchens according as the animal is young or old. Muscular contraction undergoes nearly the same changes as the nutrition of the muscles. Weak, and hardly distinguishable in the foetus, its activity is augmented at birth, increases rapidly in childhood and youth, acquires its highest degree of perfection in the adult age, and finishes by being nearly lost in decrepitude. OF THE VOICE. We understand by the voice the sound produced in the larynx, at the moment the air traverses this organ, either to enter into or pass out from the trachea. For the purpose of explaining the mechanism by which the voice is produced and modified, we shall say a few words of the manner in which sound is produced, propagated, and modified in wind instruments, especially in those which have the greatest analogy with the organ of voice. In general, a wind instrument is formed by a straight or curv- ed tube, in which the air is thrown into a state of vibration by various processes. Wind instruments are of two sorts; the one is called a mouth, the other a reeded instrument. The mouth instruments include the horn, trumpet, flagelet, flute, and the flute tube of the organ. In all these, the column of air is contained in the tube1, which is the sonorous body. In or- der that it may produce sound, it is necessary that vibrations 192 FUNCTIONS OF RELATION. should be excited. The means employed for this purpose vary according to the kind of instrument. The length, size, form of the tube, the openings formed in its side and its extremities, the force and manner with which the vibrations are excited, are the causes of the variety of sounds in different instruments. The na- ture of the substance of which they are formed only influences the timbre of the sound. The theory of these instruments is precisely similar to that of the vibration of longitudinal cords. When we know the physical condition of one of these instru- ments, we can determine with accuracy, by calculation, the sounds which it will produce. There is nothing obscure in this theory, except some point relative to the mouth-piece, that is, the manner in which the vibrations are excited. There is no very evident resemblance between this kind of instrument and that of the voice. It is more important for us to understand reeded instruments, because the organ of the voice is of this kind. Unfortunately, their theory is much less perfect than that of mouth instruments. We include in this kind of instruments the hautboy, bassoon, clari- net, and the organ of the human voice. We may divide these in- struments into the reed and the body, or tube; the mechanism of these two parts is essentially different. The reed is formed sometimes of one, and at others of two thin plates, which are capable of moving very rapidly, and the vibrations of which are destined alternately to intercept, and transmit a current of air. This is the reason why the sounds thus produced are not governed by the same laws as those form- ed by elastic plates, free at one end, and fixed at the other, which excite immediately sonorous undulations in the open air, In reeded instruments, the reed alone produces and modifies the sOunds. If the reed be long, the motions are extensive and slow; of consequence, the sounds are grave. A short reed, on the con- trary, produces, necessarily, acute sounds, because the alternate transmission and repression of the current of air are more rapid. The most perfect reed, and which gives the most agreeable sounds, is that invented by M. Grenier, or, rather, imitated by him from the Chinese. When we wish to draw from a reeded instrument a variety of sounds, it is necessary to vary the length of the reed. This is done by those who play upon the bassoon, clarinet, &c, when they wish to produce different sounds with these instru- ments. We may add, however, as an important circumstance, that the elevation of the note produced by an instrument depends, in part, on the elasticity, weight, and even form of the reed, and the in- tensity of the current of air; for when these circumstances vary, the length remaining the same, the note alters. We never employ the reed alone, but adapt it always to a tube, through which the air passes when it is forced through the reed, and which must, for this reason, be open at both extremi- ties. The length and rigidity of the tube does not influence the OF THE VOICE. 193 tone of the sound, but only the intensity of the timbre, and the possibility of making the reed speak. If it be formed by mem- branous laminae, which vary in thickness, elasticity, and tension, they may essentially affect the tone, as shown by the beautiful experiments of M. Savart. Short tubes especially modify the intensity. Those which determine the most brilliant sounds are conical tubes, which enlarge as they approach the part where the air escapes. If the cone be reversed, the sound be- comes dull. But if two equal cones, opposed base to base, are adjusted to a conical tube, the sound becomes round and strong. The reason of these modifications has never been given by natu- ral philosophers. A column of air vibrating in a tube can produce only a cer- tain number of determinate sounds. In consequence of this, a reeded instrument, when it is long, can only transmit distinctly those sounds which it is intended to produce; it is also necessary to establish at first a eertain proportion between the reed and the body of the instrument. Of consequence, when we wish to draw a succession of different sounds from the same reeded instrument, it is necessary not only to vary the length of the reed, but to modify also, in a corresponding manner, the length of the tube; now this end is attained by piercing the sides of the bassoon, clarinet, . Sulphate ) Sub-carbonate of lime "^ 2.10 2.00 " of magnesia 1 Phosphate of lime > 0.91 0.87 " of magnesia " of iron J Loss..... 1.00 1.61 Total 1000.00 1000.00 The serum sometimes presents a whitish, milklike appearance, from which it has been supposed that it contains chyle ; the sub- stance that gives to it this appearance resembles oil. The crassamentum of the blood is chiefly formed by the fibrine and colouring matter. When separated from the colouring matter, the fibrine is solid, whitish, insipid, and inodorous; it is heavier than water, does not produce any action upon vegetable colours; it is elastic when it is humid, and becomes brittle by dessication ; by distillation, it furnishes a large quantity of the carbonate of am- monia, and a large mass of carbon, the ashes of which contain a considerable quantity of the phosphate of lime, a little of the phos- VENOUS BLOOD. 357 phate of magnesia, carbonate of lime, and carbonate of soda. One hundred parts of fibrine are composed of Carbon.......53.360 Oxygen . Hydrogen Azote Total . 19.685 7.021 19.934 100.000 The colouring matter is soluble in water and the serum of the blood. When examined by a microscope, after being dissolved in these fluids, it appears, like most parts of the fluids in the ani- mal economy, to consist of small globules; when dried, and cal- cined afterward in contact with the air, it melts, bursts up into bubbles, burns with a flame, and forms a carbon, which cannot be reduced into ashes but with extreme difficulty. This carbon, du- ring its combustion, disengages ammoniacal gas, and furnishes a hundredth part of its weight of ashes. It is composed of Oxide of iron......55.0 Phosphate of lime and a trace of the phos- ) ~ n phate of magnesia j Pure lime.......17.5 Carbonic acid . . . . . . 19.5 Total.......100.0 It is important to remark, that there is not found in any part of the blood either gelatin or phosphate of iron, as was formerly believed. The respective proportion between the quantity of the serum and the crassamentum, those of the colouring matter and fibrine, have not been carefully examined, as we shall see hereaf- ter. It is probable that they are varied by an infinite number of circumstances. M. le Canu, in his valuable work already cited, in twenty two comparative experiments, made on persons differing in age, sex, and temperament, gives the following results: In 1000 parts of Blood. Dry Fibrine. Humid Fibrine Maximum . . 7.233 28.940 Minimum . . 1.360 5.440 We thus see how the proportion of this element may vary. The coagulation of the blood has been, in turn, attributed to cold, the contact of air, and a state of rest; but John Hunter and Hewson demonstrated, by experiment, that this phenomenon could not be referred to either of these causes. Hewson took fresh blood and froze it, by exposing it to a low temperature; the blood was afterward melted, and it became fluid, and shortly coagulated as usual. John Hunter obtained a similar result Thus it was proved that coagulation of the blood is not produced by cold. It seems even that a temperature somewhat high is favourable to 358 NUTRITIVE FUNCTIONS. its coagulation. Experiment also proves that the blood runs into a mass when deprived of the contact of air, and agitated ; in gen- eral, however, repose, and the contact of air, favour its coagulation. But so far from referring the coagulation of the blood to any physical influence, it must undoubtedly be considered as essen- tially vital; that is, as giving demonstrative evidence that the blood is endowed with life. We shall see, hereafter, of what importance the property of coagulating, possessed by the blood and other fluids, is in many of the phenomena of nutrition. To form a more pre- cise idea of the coagulation of the venous blood, I placed in the focus of a microscope a drop of this fluid while it was still in a liquid state; it appeared like a red mass, but, as soon as it began to coagulate, the edges became transparent and granulated; the solid part, being almost opaque, formed an infinite number of fine meshes, or cells, which contained the fluid part, which was the most transparent. It was this disposition which gave to the edge of the drop of blood its granulated aspect. By degrees these meshes became enlarged by the retraction of the solid parts; in many places they entirely disappeared, and there only remained between the external circumference of the drop of blood and the edge of the central coagulum an arborescent appearance, very analogous to what we have described in speaking of the lymph; their divisions communicating with each other like the vessels and nerves of leaves. This experiment must be made by a diffused or artificial light, for the direct light of the sun produces dessica- tion, without coagulation. Under many circumstances the blood coagulates, even when contained in the vessels; but in general this phenomenon arises from disease. Some authors thought they had remarked that the blood, in coagulating, became warmer; but John Hunter, and very recently Mr. J. Davy, have proved that there is no elevation of temperature. At the period when galvanism attracted so much attention in France, it was supposed that if a portion of the coagulum, re- cently formed, was submitted to a galvanic current, it contract- ed itself like the muscular fibres. I have often endeavoured to produce this effect, by submitting portions* of coagulum, at the moment of their formation, to the action of the pile; but I have never seen anything of the kind. I have varied these attempts in different ways, but have never been more fortunate. Very re- cently I have repeated this experiment, with M. Biot, but the re- sult was the same. The analysis of the coagulum of venous blood by M. le Canu has given the following result; VENOUS BLOOD. 3i Water 1st Analysis. . 780.145 2d Analysis 785.590 Fibrine . 2.100 3.565 Albumen . 65.090 69.415 Colouring matter . 133.000 119.626 Fatty crystallizable matter Oily matter . 2.430 . 1.310 4.300 2.270 Extractive matter soluble in al- ) , 7q0» cohol and water ) 1.920 Albumen combined with soda . 1.265 2.010 Chlorine of sodium ^ " of potassium 1 Sub-carbonate > . 8.370 7.304 Phosphate Sulphate J Sub-carbonate of lime "^ • " of magnesia Phosphate of lime " of magnesia " of iron ► . 2.100 1.414 Peroxide of iron J Loss .... . 2.400 2.586 Total 1000.000 1000.000 The analysis of the venous blood, such as we have already pointed out, makes us acquainted with the peculiar elements of this fluid; but as all the substances absorbed in the intestinal ca- nal, the serous membranes, and the cellular tissue, are mixed im- mediately with the venous blood, the result must be, that the com- position of this fluid will vary in proportion to the matter absorb- ed. There will be found, under different circumstances, alcohol, aether, eamphor, and salts, which it does not contain generally, when these substances have been submitted to absorption, in any part of the body. The greater or less degree of promptitude with which the blood runs into a mass, the solidity of the eoagu- lum, the separation of the serum, the formation of an albuminous coat upon its surface, and the particular temperature of the fluid in or out of the vessels, are phenomena which we shall examine in the article Arterial Blood. Apparatus of the Venous Blood. • This is composed, first, of the veins ; second, of the right auricle and ventricle of the heart; third, of the pulmonary artery. Of the Veins. The arrangement of the veins in the tissue of the organs es- capes our senses. When we first begin to distinguish them, they are presented under the form of an infinite number of small tubes, exceedingly delicate, communicating with each other in a sort of very fine net-work; they soon mcrease in volume, still preserving their reticulated arrangement. They in this manner form ves- 360 NUTRITIVE FUNCTIONS. sels, the capacity, form, and disposition of which differ in each tissue, and even in each organ. Some organs appear almost en- tirely formed of venous radicles; such are the spleen, the cav- ernous parts of the penis, the clitoris, the iris, the nipple, and the ureter, &c. When we force an injection into one of the veins which pass out from these different tissues, they but rarely be- come entirely filled with the injected matter, which does not happen often, when the injection is pushed into the arteries. The incision of these parts in man, or in living animals, causes blood to be thrown out, which has all the appearance of venous blood. The venous extremities communicate with the arteries and lymphatic vessels ; anatomy leaves no doubt on this point; but it appears that those extremities, the disposition of which is un- known, are also open On the different surfaces of the membranes, the cellular tissue, and even the parenchyma of the organs. M. Ribes, having forced mercury into one of the branches of the vena portae, saw the villosities of the intestinal mucous membrane filled with this metal, which spread itself into the cavity of the in- testine. In forcing air from the venous trunks towards their or- igin, and overcoming the resistance of the valves, which is very easy in those bodies which are in a state of incipient putrefac- tion, the same anatomist has always found the air spread with great facility into the cellular membrane, although no sensible rupture of the venous walls had taken place. I have made simi- lar remarks in forcing the air, or other fluids, into the veins of the heart. These facts, which have taken place since my experiments on venous absorption, of which I shall speak hereafter, agree per- fectly with them. The veins of the brain surround it on every side ; they form a great part of the pia mater, and penetrate into the ventricles, where they contribute to form the plexus choroides. Those of the testicles represent a very fine net-work, which covers the spermatic vessels, while those of the kidneys are short and volu- minous. In leaving the organs to pass towards the heart, the veins affect a very different arrangement. In the brain they are lodged between the laminae of the dura mater, protected by them, and are known by the name of sinuses. In the spermatic cord they are flexuous, anastomosing frequently, and forming the pam- pini-form body; About the vagina they are reticulated, in the uterus they are very voluminous, with numerous flexuosities. In the extremities, head, and neck they are distinguished into deep- seated, which accompany the arteries, and superficial, which are placed immediately under the skin, in the midst of the lymphatic trunks, which are found there. In proportion as the veins be- come distant from the organs, and approach the heart, they di- minish in number and increase in volume, so that all the veins of the body, which are innumerable, terminate in the right ventricle of the heart by three trunks, the vena cava, inferior and superior. and the coronary vein. VENOUS BLOOD. 361 I have said that the small veins communicate with each other by frequent anastomoses ; this disposition exists also in the large veins, and in the trunks of the veins. The superficial trunks in the extremities communicate with the deep-seated; the veins of the external part of the head, with those of the internal; the ex- ternal, with the internal jugulars ; and the vena cava superior, with the inferior, &c. These anastomoses are advantageous to the course of the blood in these vessels. Many veins exhibit in their cavities,folds of a parabolic form, called valves; they have two free surfaces, and two edges, the one of which adheres to the walls of the vein, while the other is left floating in it. The first is more distant from the heart, and the other much nearer to it. The number of the valves are not always the same: in general they are the most numerous where the blood has to rise against its own gravity, and they have only a weak pressure to support them from the surrounding parts; they are wanting, on the con- trary, in those parts where the veins are exposed to an habitual pressure, which favours the circulation of the blood, and in those which consist of canals not extensible. They rarely exist in those veins which are less than a line in diameter. Sometimes the size of the valves is so great as to fill completely the cavity of the vein; but at others they are evidently too small to produce this effect All anatomists have thought that this arrangement depemded on primitive organization; but Bichat thought he had discovered that it arose from the state of contraction or dilatation of the veins when death took place. I have endeavoured to satisfy myself of the correctness of Bi- chat's idea ; but I acknowledge I have been unable to do it. I have not perceived that the distention of the veins had any influ- ence upon the size of the valves ; it has seemed to me, on the con- trary, that they remain always the same ; but that their form was altered by their contraction or dilatation; and it was probably this which deceived Bichat. The veins are formed by three membranes, placed one over the other. The external is cellular, dense, and difficult to rupture. If we can depend on the works of anatomists, that which comes next is formed of parallel fibres in the direction of the length of the vessel; and that this is easiest to be perceived when the vein is large and contracted. I have endeavoured, but without suc- cess, to distinguish the fibres of the middle membrane of the vein. I have always observed excessively numerous filaments interla- ced in all directions, but which seemed to assume the appearance of longitudinal fibres when the vein is folded longitudinally, a dis- position which is always observed in the large veins. The sub- cutaneous veins of the extremities, the walls of which are very thick, will be found to afford the greatest facility in examining the arrangement of this membrane. We are ignorant of the chemi- cal nature of the fibrous coat of the veins; from some experiments which I have made, I suspect it is chiefly fibrine. It is extensible and firm, and does not present otherwise any peculiarity in the 362 NUTRITIVE FUNCTIONS. * living animal, in which it resembles muscular fibres. When irri- tated with the point of a scalpel, or submitted to a current of gal- vanic fluid, it does not exhibit any sensible contraction. The third membrane of the veins or internal tunic is extremely thin, and very much folded on that surface which is in contact with the blood; it is very flexible and extensible, at the same time pre- senting a considerable resistance; it supports, for example, with- out being ruptured, the pressure of a ligature drawn strongly around it. Some of the veins, for example, the sinuses of the brain, the venous canals of the mouth, and the sub-hepatic veins, have their walls alone formed by this membrane, being almost entirely destitute of the two others. These three tunics together form a very elastic tissue. In whatever direction the veins may be enlarged, they resume im- mediately their primitive form ; nor can I imagine on what ground Bichat has asserted that they are destitute of elasticity. Nothing can be easier than to satisfy ourselves that they possess this phys- ical property to a very great extent. Another physical prop- erty that the walls of the veins possess in a very high degree is that of imbibition. They act in this respect, after death and du- ring life, like sponges with very fine cells, filling themselves with any liquid brought in contact with them. A large number of arter- ies and veins, called the vasa vasorum, and filaments of the great sympathetic, are sent to the veins; they are, therefore, far'from being exempted from those diseases to which the other parts of the animal body are subject. They are sometimes affected by in- flammation. Of the Right Cavities of the Heart. The heart is so well known, that it seems hardly necessary to insist much upon its form and structure. I shall only allude to its principal characters. In man, the mammalia, and birds, it is formed into four cavities ; two superior, which are called auricles, and two inferior, which are called ventricles. The left auricle and ventricle belong to the apparatus of the arterial blood; the auricle and ventricle of the right side make a part of that of the venous blood. It is not very easy to describe the form of the right auricle; its transverse diameter is the greatest; its cavity exhibits, at its posterior part, openings from the vena cava, superior and inferior, and coronary vein; internally it presents a depression called the foramen ovale, which is open in the foetus, but closed in the adult. At the bottom of the auricle is a large opening, which conducts into the right ventricle. The internal surface of the auricle pre- sents a greater number of fleshy masses or columns, which are rounded or flattened, and which cross each other in various direc- tions, exhibiting a sort of spongy tissue spread over the internal surface of the auricle, and forming a coat of considerable thick- ness. At the place where the vena cava inferior is connected with the auricle is a fold of the internal membrane, which is call- ed the Eustachian valve. VENOUS BLOOD. 363 The external and anterior face of the right ventricle is very near to the sternum, so that it is brought in contact with it when its cavity is distended with blood. We shall see hereafter the im- portance of this remark. The right ventricle is a more spacious cavity, and has thicker walls than the auricle; it is of the form of a triangular pyramid, the base of which corresponds to the auri- cle and pulmonary artery, and its apex to that of the heart; all its surface is covered with long and rounded projections, which are called columnee carneee; their arrangement*is very irregular; like those of the auricle, they form a reticulated or cavernous tis- sue through the whole extent of the ventricle, particularly to- wards its apex. The columnse carneae of the ventricle, being gen- erally larger than those of the auricle, form also a network, the meshes of which are coarser; some arising from the surface of the ventricle, terminate in forming one or more tendons, which are attached to the loose edge of the tricuspid valve, which is pla- ced at the opening, by which the auricle and ventricle communi- cate with each other. At the side, and a little to the left of this, is the orifice of the pulmonary artery. The walls of the auricle and ventricle are formed of three tunics: the one exterior is of a serous nature; the internal is analogous to that of the internal membrane of the veins; and the middle is chiefly muscular and contractile ;* this coat is thin in the auricle, but of great thickness and strength in the ventricle. The innumerable fibres which compose it have a very intricate arrangement; many respectable authors have endeavoured with great labour to ascertain their direction; but notwithstanding their patience and address,^he dis- position of these fibres is still but little known. Happily, it is not necessary for us to form an exact idea on this point to enable us to comprehend the action of the auricle and ventricle. The heart has arteries, veins, lymphatic vessels, and nerves, which arise from the great sympathetic, and are distributed to its walls and arter- ies, and perhaps even to its muscular tissue. Of the Pulmonary Artery. This artery arises from the right ventricle, and passes towards the lungs. At first it forms but a single trunk; soon it becomes divided into two branches, one of which is sent to the right, and the other to the left lung; each of these branches are divided and subdivided until they form an infinite number of small ves- sels, the tenuity of which is so great that they are at least imper- ceptible by our senses. The divisions and subdivisions of each of these branches of the pulmonary artery are remarkable in this, that they do not communicate with each other before becoming extremely small; the last divisions appear to be continuous im- mediately with the roots of the pulmonary veins. The pulmo- nary artery is formed of three tunics : the external is very strong, and of a cellular texture ; the internal is very smooth on its inter- nal surface, and is always lubricated by a thin fluid; the mid- dle tunic has circular fibres, which are very elastic, and were 364 NUTRITIVE FUNCTIONS. long thought to be muscular, though they evidently do not pos- sess that character; its chemical nature was ascertained with precision by M. Chevreul. It is formed by the yellow elastic tis- sue ; an immediate principle, distinct from all others. It is to this tissue that the artery principally owes its elasticity. But this property is only preserved while the tissue is penetrated by wa- ter ; when deprived of it, it becomes friable. It is, then, highly probable that the yellow membrane of the pulmonary artery im- bibes continually the aqueous part of the blood, and thus preserves its great elasticity, its peculiar characteristic. The tissue of the walls of the artery, and of the pulmonary capillaries, easily imbibes all the substances with which it happens to be brought in con- tact. Like all the membranes, it is readily traversed by vapours and gases. Course of the Venous Blood. According to the most distinguished physiologists, this is still but imperfectly understood. We shall only describe at present its most apparent phenomena, reserving more doubtful questions until we speak on the relations which exist between the course of the blood in the veins and arteries. We shall then speak of the cause which determines the entrance of the blood into the venous extremities. In order to form a general, but just idea, of the course of the blood in the veins, it is necessary to recollect that the sum total of the cavities of the small veins forms a much lar- ger cavity than those of the large, into which they pour their con- tents ; and these, again, bear the same relation to the trunks in which they terminate. In consequence of this, the blood which goes from the extreme veins passes always from a larger to a smaller cavity. The following hydrostatic principle is, therefore, perfectly applied in this instance. When a fluid passes through a tube which is full, the quantity which traverses in a given time the different sections of the tube must be always the same; but when the tube becomes larger its velocity diminishes, and increas- es when the tube is smaller,. Experience confirms the exactness of this principle, and the justness of its application to the course of the venous blood. If we cut across a small vein, the blood passes out very slowly, but it escapes much more rapidly from a large vein. Many veins are destined to transport the blood contained in an organ towards the large trunks. In consequence of their frequent anastomoses, the compression, or even tying one .or more of the veins, does not pre- vent, nor even diminish the quantity of blood which is returned towards the heart; it only acquires a greater degree of velocity in the veins which remain open. When a ligature is applied about the arm, preparatory to performing the operation of bleeding, the following phenomena take place. In the ordinary state, the blood which is carried to the forearm and hand returns towards the heart by four deep-seated, and at least as many superficial veins. When the ligature is passed around the arm, the blood no longer VENOUS BLOOD. 365 passes by the sub-cutaneous veins, and traverses with difficulty those which are deep-seated. If one of the veins be then opened at the fold of the arm, a continued jet will be formed, which lasts as long as the ligature remains tight, and ceases when it is re- moved. We often find the veins not much distended with blood ; when, however, this fluid passes with the greatest rapidity, the reverse is the fact. In the extreme veins it is very little the case. For a reason easy to be understood, those circumstances which acceler- ate the motion of the blood in the veins increase also the disten- tion of the vessels. The introduction of the blood into the veins taking place in a continuous manner, every cause which operates as an obstacle to its course produces a distention of the vein, and a greater or less degree of stagnation of the blood. The walls of the vein appear to have a very feeble influence upon the course of the blood. They yield easily when its quan- tity is increased, and contract again when it is diminished. But this contraction is extremely limited; it is not sufficient to expel the blood entirely from it; this is constantly found to be the case in the recent subject. I have often seen the veins empty in the living animal, and at other times I have observed that the col- umn of fluid was far from filling up entirely the cavity of the vessel. A great number of the veins, such as those of the mouth, the sinuses of the dura mater, testicle, and the liver, the walls of which form inflexible canals, can have no influence upon the motion of the blood that passes through their cavities. The venous blood that is poured into many of the tissues, particularly the spongy tissue of the vertebrae, can evidently receive no impulse from the walls of the cavities through which it passes. We must attribute always the faculty which the veins have of contracting when the column of blood is diminished, to the elasticity of their walls, and not to a contraction which has any analogy to that of the muscles. This contraction is much more remarkable in those which have thick walls like the superficial veins. If the veins have of them- selves but little influence upon the course of the blood, there are many auxiliary causes the action of which is very manifest. All compression, whether continued or alternate, exerted upon a vein can, when it is sufficiently strong to flatten the vein, obstruct the passage of the blood. If it be moderate, it opposes the dilatation of the vein from the pressure of the blood, and thus favours its motion. The habitual pressure which the skin of the extremities exerts upon the veins running beneath it, is one cause which renders the course of the blood in these vessels more rapid and easy. We cannot doubt this, as those circumstances which diminish the con- tractility of the tissue of the skin are, sooner or later, followed by a considerable dilatation of the veins, and in some cases the pro- duction of varices. It is also known that an appropriate bandage restores the veins to their ordinary dimensions, and the course of the blood to the internal parts. In the abdomen, the veins are 366 NUTRITIVE FUNCTIONS. submitted to the alternate pressure of the diaphragm and abdom- inal muscles; a cause which is favourable to the progress of the venous blood in this part. The veins of the brain support also a considerable pressure, which must produce the same result. Whenever the blood in the veins passes in the direction of its weight, its progress is much easier than when it has to mount against it. We must not neglect to notice the relations of these auxiliary causes to the arrangement of the veins; where they are the most remarkable, the veins do not possess valves, and their walls are very thin, as we notice in the abdomen, chest, cavity of the cranium, &c. But where they have less influence, the veins are furnished with valves, and the walls are thicker; lastly, where they are very weak, as in the sub-cutaneous veins, the valves are numerous, and the walls of considerable thickness. If we wish to form a comparatively exact idea in this case, we have only to examine the internal saphaena, the crural, and the commencement of the external iliac veins, on a level with the opening of the femoral aponeurosis, destined for the passage of the saphaena vein; the contrast in the thickness of the walls will be found very striking. I have lately made this comparison in the body of a criminal who was very muscular. The walls of the saphaena were as thick as those of the carotid artery; the crural, and especially the external iliac, had walls which were much thinner. We must take care, however, lest we confound these circum- stances, favourable to the course of the blood in the veins, with causes which act in a very different manner. For example, it is generally known that the contraction of the mtfscles of the fore arm and hand, during bleeding, accelerates the .motion of the blood which escapes through the opening of the vein. Physiolo- gists assert that the muscles, in contracting themselves, compress the deep-seated veins, and expel the blood, which passes then into the superficial veins. If this were the case, the acceleration would be only instantaneous, or, at least, of very short duration; while it is known to continue, in general, during the contraction. We shall see hereafter how this phenomenon may be explained. When the feet are plunged for some time in warm water, the sub- cutaneous veins swell: this is generally attributed to the rarefac- tion of the blood. The true cause appears to me to be the in- crease in the quantity of the blood wnich is carried to the feet, and especially to the skin; this augmentation would naturally ac- celerate the motion of the blood in the veins, inasmuch as in a given time they are traversed by a larger quantity of blood. From the preceding remarks, we may easily understand that the venous blood must be frequently stopped, or at least its course retarded, either from the too great pressure which the veins ex- perience in the different positions that the body assumes, or by different foreign bodies which are applied to it, &c. Hence the necessity of the numerous anastomoses, which we have said exist not only between the extreme veins, but those which are larger, VENOUS BLOOD. 367 and also in the large trunks. In consequence of these frequent communications, should one or more of the veins be compressed, so as not to allow the blood to pass, this fluid is turned aside, and arrives at the heart by other routes. One of the uses of the vena azygos appears to be to establish an easy communication between the vena cava superior and inferior. I believe, however, its prin- cipal use is to afford a common termination for the greater part of the intercostal veins. There is nothing very obscure in the action of the valves of the veins; they are nothing else but true valves, which oppose the return of the blood towards the venous extremities, and which fulfil this office most perfectly when they are large ; that is, when they are favourably disposed for closing the cavity, of the vein entirely. The friction of the blood against the walls of the veins, its adhesion to these walls, and its imperfect fluidity, must modify the motion of the blood in the veins, and generally tend to retard it. But it is impossible, in the present state of physiology and hydrostatics, to assign, with precision, the particular effect of each of these causes. What we have said of the course of the venous blood is enough to show that it is very much modified by an infinite number of cir- cumstances. We shall have occasion to examine this more par- ticularly hereafter, when we come to examine generally the cir- culation of the blood, and the difference in quality between that of the arteries and veins. The venous blood from every part of the body arrives at the right auricle of the heart by three trunks, which we have already mentioned, viz., two which are very vo- luminous, called the vena cava inferior and superior, and a small one called the coronary vein. It is very probable that the blood passes through each of these veins with very different degrees of rapidity. It is evident that these three columns of fluid endeavour to penetrate into the auricle at the same time, and that this effort must be considerable. Absorption exerted by the Veins. Not only do the venous extremities receive blood directly from the extreme arteries, but they present another remarkable phe- nomenon. Every kind of gas or fluid, when put in contact with the different parts of the body except the skin, passes immediately into the small veins, and arrives soon at the lungs with the venous blood. The same thing takes place with all those solid substances capable of being dissolved by the blood or secreted fluids. In a very short time they are introduced into the veins, and are trans- ported to the heart and lungs; this introduction is called venous absorption. If we wish to form a distinct idea of this property, common to all the veins, we have only to introduce an aqueous solution of camphor into one of the serous or mucous cavities of the body, or to bury in the tissue of one of the organs a morsel of solid cam- phor. Soon after, the air which passes from the lungs of the ani- 368 NUTRITIVE FUNCTIONS. mal will possess, very distinctly, the odour of camphor. This experiment is easy to be made upon man, after the administration of an enema; it is seldom that, in the course of five or-six minutes, the breath does not exhibit strongly the odour of this drug. Al- most all the odoriferous substances which do not combine with the blood produce similar effects. In the experiments which I made upon the absorption of the veins, I have found that its rapidity varied according to the different tissues. It is, for example, much more rapid in the serous than the mucous membranes ; it is much more prompt in those tissues which abound with sanguineous ves- sels than those which contain few, &c. The corrosive quality of the fluids or solids submitted to absorption does not prevent this being effected. It appears, on the contrary, to be much more prompt than in those substances which do not attack the tissues.* The intestinal villosities, formed partly by the venous extremi- ties, absorb in the small intestine all the fluids except the chyle. It is easy to satisfy ourselves of this by introducing into the intes- tine those substances which are strongly odorous or sapid, and susceptible of being absorbed. As soon as the absorption begins, and as long as it continues, the properties of these substances may be recognised in the blood taken from the branches of the vena porta, though we cannot distinguish them in the lymph until a considerable time after the absorption has begun. We shall show, in the sequel, that they do not arrive at the thoracic duct through the medium of the lacteal vessels, but through the communications of the arteries with the lymphatics. It is well known that all the veins of the digestive organs unite together in a single trunk, which is divided and subdivided in the tissue of the liver. This struc- ture deserves to be noticed. In consequence of the great extent of the mucous membrane with which the drinks and other fluids are in contact, and the rapidity of their absorption by the mesen- teric veins, a considerable quantity of fluid foreign to the animal economy may traverse the venous system of the abdomen in a given time, and alter the composition of the blood. If the fluid, in this state, passed on to the lungs, and from thence to the rest of the organs, there would result the most serious consequences, as the following experiments will demonstrate. I found that fifteen grains of bile forced suddenly into the crural vein generally killed the animal in a few minutes. If a certain quantity of atmospheric air be introduced rapidly into the same vein, the same effects will follow; but an injection made in the same way into one of the -branches of the vena portae will not be found to produce any inconvenience. From whence arises the difference in these results? Does the passage of foreign fluids into the animal economy, through the innumerable small vessels * Much is said in modern works of physiology, of the peculiar sensibility of the mouths of the absorbent vessels; they are, say some, endowed with a delicate and sure tact, by which they discern those substances which are useful and suitable to them, and they re- fuse those substances which are injurious. These ingenious suppositions, which have a particular charm for minds eager after new ideas, are destroyed as soon as they are sub- mitted to experiment. VENOUS BLOOD. 369 of the liver, have the effect of mixing them more intimately with the blood, and, as it were, diluting them with a large quantity of this fluid, so that their chemical nature becomes somewhat alter- ed ? This becomes the more probable from the circumstance that, if the same quantity of bile or air be injected very slowly into the crural vein, it does not produce any sensible injury. It is, therefore, perhaps necessary that the veins arising from the di- gestive organs should pass through the liver, in order that they may mix more intimately with the blood the substances absorbed in the intestinal canal. Whether this effect takes place or not, it cannot be doubted that those agents which are absorbed from the stomach and intestines do pass immediately through the liver, and that they cannot but have an influence upon this organ which mer- its the attention of physicians.* We have said above that the skin makes an exception to the general law that the veins absorb in every part of the body. This proposition merits a particular examination. When the skin is deprived of the epidermis, and the sanguine- ous vessels which cover the external surface of the chorion are exposed, absorption takes place, as it does in every other part. After having applied a blister, if we cover the surface, which has been deprived of its epidermis, with a substance the effects of which upon the animal economy we can easily observe, a few minutes are often sufficient for them to be manifested. Caustics applied to ulcerated surfaces have often produced death. In or- der that the inoculation of the smallpox, or the vaccine disease, may succeed, it is necessary to take care to place the substance beneath the epidermis, and, of consequence, to place it in contact with the subjacent sanguineous vessels. But it is very different when the skin remains covered with its epidermis. Unless the substances in contact with it are of a na- ture to change its chemical composition, or to excite an irritation in the corresponding sanguineous vessels, there is no sensible ab- sorption. I know that this result is contrary to the received opin- ion on this subject. We think, for example, that when the body is plunged in a bath, it absorbs the surrounding liquid; it is on this idea that the use of nourishing baths of milk and soup was founded. In a work recently published, M. Seguin has placed the point beyond doubt, that the skin does not absorb water when placed in it, by a series of very careful experiments. To satisfy himself if the same thing would take place with other fluids, this gentleman made the following experiments upon persons affected with syphilitic diseases. He plunged their feet and legs in baths composed of sixteen pounds of water, with one ounce of corrosive sublimate dissolved in it; each bath lasted one or two hours, and * It would be curious to inquire why, of all the vessels of the liver, the branches of the vena portae alone, by the disposition of their external membrane, called the capsula glissonii, are capable of contracting upon themselves when the quantity of blood which runs through them diminishes. Perhaps this arrangement is most favourable to the course ofthe venous blood,-which, to this portion of the vena portae, passes from a narrow part into one that is large, while everywhere else it passes from a part that is large into one that is narrow. A A A 370 NUTRITIVE FUNCTIONS. was repeated twice, daily. Thirteen patients were submitted to % this treatment during twenty-eight hours, who did not present any evident marks of absorption; a fourteenth patient presented signs of this having taken place after the third bath, but he had excon- ations on both his legs ; two others who were in the same situa- tion exhibited the same phenomenon. In general, absorption does not take place, excepting in those persons where some portion of the epidermis is removed ; however, at a temperature of 72° Fah- renheit, the corrosive sublimate is sometimes absorbed, but the water never. Among the experiments of M. Seguin, there is one which ap- pears to throw great light upon the absorbing faculty of the skin. After having weighed seventy-three grains of calomel, the same quantity separately of gamboge, scammony, salt of Alembroth, and tartar emetic, M. Seguin caused a patient to lie down on his back ; and having washed the skin of the abdomen nicely, he ap- plied carefully upon the surface these five substances; he then covered each of the places with a watch-glass, maintaining it in its situation with a linen bandage. The heat of the chamber was kept at about 68° Fahrenheit. M. Seguin remained with the patient the whole time, in order to prevent mistakes ; the experiment last- ed during ten hours and a quarter. The glasses were then re- moved, and the substances collected with great care, and weighed. The calomel was reduced to seventy-one grains and a third ; the scammony weighed seventy-two grains and three quarters ; the gamboge, a little more than seventy-one grains ; the salt of Alembroth was reduced to sixty-two grains, several pustules be- ing developed on the spot where it was applied ; the emetic tartar weighed sixty-seven grains. It is evident, from this experiment, that those substances which were the most disposed to irritate the skin, and combine with the epidermis, were partly absorbed, while with the others this was not the case. But that which does not take place from a simple application may take place from frictions upon the skin with certain substan- ces. We cannot doubt that mercury, alcohol, opium, camphor, vomits, purgatives, &c, penetrate by means of the venous system. It appears that these different agents pass through the epidermis either through the pores, or are insinuated into the openings by which the hairs or insensible transpiration pass out. Thus, in con- sidering the absorption of the skin, we perceive that this mem- brane differs from trie other surfaces of the body only in being covered by the epidermis. While this coat remains perfect, and is not perforated by the substances placed in contact with the skin, no absorption takes place ; but whenever this is the case, this ac- tion occurs in the skin as in every other part. I am not ignorant that many persons will be surprised at my not hesitating to attribute to the veins the faculty of absorption, while the general opinion is that all absorption is effected by the lymphatic vessels. But from the facts already related under the article Absorption of the Lymph, and some others which I am now VENOUS BLOOD. 371 about to add, it is impossible for me at present to think otherwise. Besides, the opinion which I support is by no means new; Ruysch, Boerhaave, Meckel, and Swammerdam professed it, and Haller supported it, though he was not ignorant of the anatomical labours of John Hunter. M. Delille and myself separated the thigh of a dog from the body after having first stupified him with opium, for the purpose of avoiding the pain inseparable from a tedious ex- periment. We left the crural artery and vein alone untouched, preserving thus the communication between the thigh and trunk. These two vessels were dissected with very great care; that is, they were insulated to about the extent of two inches; their cel- lular coat was removed, lest it should conceal some lymphatic vessels. Two grains of a very subtle poison (upas tiente) were then introduced into the foot. The effects of the poison were as prompt and severe as if the thigh had not been separated from the body, so that the effects were manifested before the fourth minute, and the animal died before the tenth. It may be objected, notwithstanding all the precautions which were taken, that the walls of the crural artery and vein still con- tained lymphatics, and that these vessels were sufficient to give passage to the poison. To do away this objection, I repeated upon another dog the preceding experiment, with this difference: I introduced into the crural artery the barrel of a small quill, upon which I fixed the vessel by two ligatures; the artery was divided in a circular direction between the two ligatures ; I then did the same with the crural vein; thus all communication be- tween the thigh and the rest of the body was interrupted, except the arterial blood, which passes to the thigh, and the venous which returned from it. The poison introduced into the foot pro- duced its effects in the ordinary time ; for example, about four minutes. From this experiment, we cannot doubt that the poison did pass from the foot to the trunk through the crural vein. To render this phenomenon still more evident, we have only to press the vein between the fingers at the moment when the poison is beginning to develop itself; these effects cease soon, but they return as soon as the vein is left free, and cease if we compress it anew. We may thus graduate them according to our pleasure. We may add to these facts, which appear to me to be decisive, the interesting experiments made by Flandrin. In the horse, the substances con- tained both in the large and small intestines are generally mixed with a large quantity of liquid, which is more or less abundant as we approach towards the rectum; it is absorbed as it passes over this part of the intestinal canal. Now Flandrin ascertained that the fluid contained in the lacteal vessels did not possess any odour analogous to that of this intestinal fluid; but, on the other hand, that the venous blood of the small intestines had sensibly an her- baceous taste ; that of the ccecum had a sharp and slightly urinous taste; that of the colon possessed the same character in a more remarkable degree. The blood in the other parts of the body presented nothing of the kind. 372 NUTRITIVE FUNCTIONS. A half pound of assafoetida, dissolved in an equal quantity of honey, was given to a horse; the animal was afterward fed in the usual way, and killed in about sixteen hours. The odour of the assafoetida was very distinct in the veins of the stomach, small intestines, and coecum; it was not remarkable in the arterial blood nor the lymph. Under the article Lymphatic Vessels, I have spoken of the experiments of John Hunter, to prove that these vessels are the only agents of absorption. That author endeavoured also to demonstrate that the veins do not absorb; but these last are not more satisfactory or correct than those which we have already mentioned. " I took," says Hunter, " a portion of the intestine of a sheep; after having divided the abdominal walls, I passed liga- tures upon its two extremities, and then filled it with warm water. The blood which returned by the veins of this part did not ap- pear more diluted or lighter than that of the other veins. I then tied the artery and all its communications, and examined the state of the vein. It was not swelled, the blood was not more diluted, and it did not give any indication of the presence of the water in its cavity. The veins, therefore, do not absorb."* How many objections present themselves to this experiment in the minds of those who think precision desirable in physiological inquiries ! How could John Hunter know, from the simple ap- pearance immediately after the experiment was performed, that the water was not absorbed, and not mixed with the blood of the vein ? Again, how could this author, otherwise so eminent, have supposed that the action of the vein would continue when a liga- ture was passed around the artery? It would have been first necessary to determine the effect of tying an artery upon the mo- tion of the blood in the corresponding vein; a thing which had never been done. In another experiment, the same physiologist injected warm milk into a portion of the intestine ; shortly after- ward he opened the mesenteric vein, and collected the blood as it passed out, and because he could not distinguish any trace of the milk, he concluded that no absorption of this fluid had taken place by the vein. But at the time of Hunter, they were far from possessing any means of detecting a small quantity of milk in a certain quantify of blood. At the present period, when animal chemistry is far more advanced, it is a difficulty not easily over- come. These two experiments, when fairly considered, ought not to have any influence in deciding the doctrine of venous absorption. The other experiments, the number of which is six, are far from being conclusive, but, on,the contrary, are still more defective. In a word, if it were necessary to adduce stronger evidence in favour of venous absorption, I would refer the reader to many parts of the body in which the most expert anatomists have never been able to detect lymphatic vessels, or any other but blood-vessels, such as the eye, the brain, the placenta, &c, though absorption * Medical Commentaries, chap. v. VENOUS BLOOD. 373 takes place with the same promptitude as in every other part of the body. I will add, that all those animals which do not possess vertebrae have blood-vessels, but not lymphatics, while absorption still manifestly takes place. Finally, the thoracic duct is much too small to afford a passage to all the substances ab- sorbed in the various parts of the body, and particularly the drinks.* All these phenomena are at once satisfactorily explained when the absorption of the veins is admitted. Facts, experiments, and reason, then, concur in favour of the doctrine of venous absorption, f Such was the state of this question when the first edition of this work was published. But since that time science has taken an important step; it has lost a prejudice, and acquired a fact of extreme interest. It was believed, for at that time physiology consisted of creeds, that the living tissues, particularly the membranes, the walls of the vessels, &c, in consequence of their vitality, were incapable of imbibing various substances which they readily imbibed afteT death. With this idea, it was attempted to explain absorption as a vital phenomenon. No one thought of regarding it as a physi- cal phenomenon. Even to me, who had laboured twenty years on this subject, the idea never occurred. Extreme repugnance to acknowledge our ignorance, and a disposition to fill with fiction the voids left in science, are intellectual phenomena as remarka- ble as they are injurious to the progress of knowledge. The mode by which absorption takes place was unknown. Instead of directly confessing this, and entering upon proper researches to discover it, it was said " that the living tissues do not allow of imbibition, as takes place after death; that there were absorb- ent mouths which distinguished between the substances present- ed, receiving some and rejecting others." This was asserted and firmly believed, and the mechanism of absorption remained unin- vestigated and unknown. Such must always be the consequen- ces when the sciences are left to the dominion of the imagination instead of being guided by observation and experiment. But I have demonstrated, by a series of experiments since that time, that the living tissues imbibe all the liquid substances which are in contact with them. The same thing also occurs with solid substances, provided they are soluble in the humours, particularly the serum of the blood. This general fact being established, ab- sorption, which has so much occupied physiologists, exercised their imaginations, and caused so many controversies, becomes a sensible and almost purely physical phenomenon. It is no longer necessary to inquire whether the veins or lymphatics absorb, in- asmuch as all the tissues are endued with this property. The following experiments, I conceive, place this beyond doubt. * Some persons drink as much as twelve pounds of mineral water in the course of a few hours, and reject it through the kidneys in the same time. , • . <■ + To recapitulate what we have said of the organs of absorption, in a general point of v Jw we mav remark, first, that it is certain that the lacteal vessels absorb the chyle; sec- nnd that it is doubtful whether they absorb anything else; third, that it has not been de- monstrated that the lymphatic vessels possess the property of absorption, but it is proved that the veins are endowed with this power. 374 NUTRITIVE FUNCTIONS. They are extracted from my memoir on the mechanism of ab- sorption.* In a public lecture on the modus operandi of medicines, I show- ed on a living animal what are the effects of the introduction of a certain quantity of warm water at 30° of the centigrade ther- mometer in the veins. In making that experiment, it occurred to me to see what would be the effect of artificial plethora on the phenom- ena of absorption. With this purpose, after having injected about a pint of water into the veins of a dog of medium size, I introdu- ced into its pleura a moderate dose of a substance the effects of which were well known to me. I was struck at observing that its effects were not perceptible until many minutes after the ordi- nary time. I immediately repeated this experiment on another animal, and obtained a similar result. In many other experiments the effects were developed at the proper time, but were sensibly weaker than might have been expected from the dose submitted to absorption, and were continued much beyond their ordinary term. In another experiment where I had introduced about two pints of water, as much as the animal could endure, the ordinary effects no longer took place ; absorption appeared to be prevented. After having waited nearly half an hour for effects which generally re- quired but two minutes to develop themselves, I came to the fol- lowing conclusion: if the distention of the sanguineous vessels is the cause of the defective absorption, if the distention ceases, the absorption ought to take place. I immediately made a large bleeding from the jugular vein, and I saw the effects manifest themselves in proportion as the blood flowed. • I might also make the opposite experiment, i. e., diminish the quantity of blood, and see if the absorption would be more prompt. This happened precisely as I had anticipated. An animal was bled to half a pound; effects which ordinarily did not occur until the end of two minutes, were exhibited in the course of thirty seconds. But it might be said that these effects were less attributable to the dis- tention of the sanguineous vessels than the change in the nature of the blood, which was opposed to absorption. To remove this objection, I made the following experiment: a free bleeding was practised in a dog, and the blood lost was replaced by an equal quantity of water, after which there was injected into the pleura a certain quantity of a solution of the nux vomica. The effects were as prompt and intense as if the nature of the blood had not been changed. Thus it is to the distention of the vessels that we must attribute the defective absorption, and not to the altered quality of the blood. Thus I became, as it were, master of a phenomenon that had been heretofore an impenetrable mystery to me. Having it in my power to prevent it, produce it, render it rapid or slow, strong or weak, its nature could not readily escape my investigation. * See my Journal de Physiologie, t. i VENOUS BLOOD. 375 In reflecting on the constancy and regularity of this phenome- non, it was no longer possible to refer it to what is called vital action, like the action of the nerves, the secretion of the glands, &c. It was much more reasonable to consider it as approaching a physical phenomenon. Among the most probable conjectures that presented themselves, was the supposition that absorption depended upon the capillary attraction of the vascular parietes for the absorbed substances; this united, indeed, all the facts that had been observed on this subject. On this supposition, solid sub- stances insoluble in the humours would resist absorption; while those, on the contrary, which are capable of combining with the tissues, or being dissolved in the fluids of the body, would become absorbed, which is conformable to the facts. Almost all liquids which are capable of moistening the vascular walls, whatever might be their chemical nature, ought, according to this view, to be absorbed, which is actually the case, as is shown by experi- ment even with caustic liquids. According to the same hypothe- sis, the more the vessels were distended, the less marked would be their absorbing power, and there would be a point at which the process would cease. The smaller and more numerous the vessels, the more rapid would be their absorption, inasmuch as the absorbing surfaces would be more extensive. This action of the walls once recognised, nothing would be easi- er than to comprehend how the absorbing substances are trans- ported towards the heart, inasmuch that, as soon as they arrived at the inner surface of the walls, they must be immediately swept into the current of the sanguineous circulation. I the more readily adopted this supposition as I recollected dis- tinctly that, in poisoning an animal by wounding it with a Java arrow in the thick part of the thigh, all the soft parts which sur- rounded the wound became of a brownish-yellow colour for sev- eral lines in thickness, having the bitter taste of the poison. But a supposition that connects together a certain number of known phenomena is, after all, but a more convenient manner of expressing them. It does not assume the character of a theory until it is confirmed by numerous and sufficiently varied experi- ments. It was therefore necessary to make new researches to ascertain how far this supposition was admissible. The affinity of the vascular walls for the absorbed matters be- ing assumed' as the cause, or, perhaps, more properly, one of the causes of absorption, this effect ought to take place after death as well as during life. This fact might easily be determined in ves- sels of a certain calibre; but keeping in mind the diameter, thick- ness, and extent of their walls relative to the capacity of the ca- nal, experiment ought to show, though it might be slight, yet ap- preciable absorption. I took a portion of the external jugular vein of a dog, this por- tion of the vessel, for an extent of about an inch and a half, not re- ceiving any braneh. I removed from it the surrounding cellular tissue, and attached to each of its extremities a tube of glass, and 376 NUTRITIVE FUNCTIONS. thus passed a current of warm water through its interior. I then plunged the vein in a liquor slightly acid, and carefully collected the warm water that passed through the interior. From the ar- rangement of the apparatus, there could not be any communica- tion between the interior current of warm water land the exterior acid liquid. At first the liquor thus collected aid not become changed, but after five or six minutes it was sensibly acid; ab- sorption had taken place. I repeated this experiment with veins taken from the human subject, with the same result. There was no obvious reason why this phenomenon should not occur in the arteries as well as the veins. I made the experiment with a portion of the carotid artery of a small dog that had died the previous evening, and with precisely the same result. I far- ther remarked, that the more acid and higher the temperature of the exterior liquor, the more promptly the phenomenon was ob- served. But this remark holds good only to a certain extent; if the temperature approach the boiling point, or if the acidity be too great, the vessel becomes horny, and the absorption very slow. If capillary absorption takes place in large vessels after death, why should it not occur during life ? If experiment did not furnish this result, all my reasonings would be confounded, and my supposition fall to the ground. I was the less assured of the success of the experiment, as I was still under the impression, of which we hear so much, of the great difference which life causes in the physical properties of the organs. But as I had frequently found occasion in my researches to doubt gen- erally-received ideas, I was not discouraged, but made the follow- ing experiment: I took a young dog about six weeks old ; at this age the walls of the blood-vessels are thin, and, consequently, favourable to the success of the experiment. I laid bear one of the jugular veins ; I isolated it perfectly through its whole length; I carefully dis- sected away the cellular tissues, and other structures by which it was surrounded, including some small vessels that ramified upon it; I placed it upon a cord, so that it should not be in contact with the surrounding parts; I then dropped upon its surface, opposite to the middle part of the cord, a thick aqueous solution of the al- coholic extract of the nux vomica. This substance acts with great energy upon dogs. I took care that no part of the poison should touch any other part than the vein and the cord, and that the course of the blood was free through the vein. Before the end of the fourth minute the effects of the poison began to be de- veloped, at first weak, but soon they were so violent that it was necessary to have recourse to inflation of the lungs to prevent immediate death. I repeated this experiment on a full-grown and much larger dog than the preceding, in which, of course, the walls of the veins were much thicker. The same effects ensued, but, as might have been anticipated, they were less prompt; the full effects were not developed until the end of ten minutes. VENOUS BLOOD. 377 Satisfied with these results as regards the veins, I was desirous of ascertaining whether the arteries possessed analogous proper- ties. But the arteries in the living animal are not in the same physical condition as the veins. Their structure is less spongy, and more dense; the walls are much thicker, and more constant- ly distended by the blood forced from the heart. It was therefore easy to foresee that if the phenomenon of absorption should take place, that it would be much more slowly developed than in the lungs. This was confirmed by experiments upon two large rab- bits, from which I dissected with great care one of the carotid ar- teries. It required more than a quarter of an hour before the so- lution of nux vomica could penetrate the walls of the artery. I ceased to moisten the vessel as soon the effects were mani- fest ; one of the rabbits immediately died. To satisfy myself that the poison had really traversed the walls of the artery, and that it had not been absorbed by the small veins that might have been overlooked in my dissection, I carefully detached the vessel that had served for the experiment. I then divided it along its whole length, and requested my assistants to taste the little blood that adhered to the inner surface of the walls. They all recognised, as well as myself, the extreme bitterness of the extract of the nux vomica. It was thus positively established that the large vessels absorb both during life and after death. It only remained to adduce di- rect proofs that the small vessels possess the same property. Their extreme tenuity, multiplicity, and thinness of the walls ap- peared to be all favourable to the production of this phenomenon. To develop it after death, it was necessary to find a membrane in the vessels of which there could be established an interior cur- rent similar to the course of the blood. I first selected a portion of the intestine, but was obliged to renounce it in consequence of considerable extravasation into the cellular tissue, and the liquid passed with great difficulty from the artery into the vein. I took the heart of a dog that died the evening before, and forced into one of the coronary arteries warm water (30° centigrade). This water returned freely through the coronary vein into the right auricle, from which it ran into a vessel. I then poured into the pericar- dium a half ounce of slightly acid water. At first, the injected water exhibited no sign of acidity; but in the course of four or five minutes, it presented unequivocal traces of it It was thus evident as respects the small vessels in the dead body. With re- spect to small vessels in the living body, it was not necessary for me to recur to new experiments, nor to sacrifice new animals. The experiments in my memoir " On the Organs of Absorption in the Mammiferi" left no doubt in this respect, according to the judgment of the Academy of Sciences. A single objection might still be offered, viz., that the mem- branes which are permeable after death do not appear to be so during life. In the dead body, the bile transudes through the pe- ritoneum, imparting a yellow colour to the parts which surround B B B 378 NUTRITIVE FUNCTIONS. the gall bladder, which does not take place during life. The per- meability of the membranes in the dead body is too notorious to be denied, but it did not appear to me a necessary consequence that the membranes are impermeable during life. Supposing that the walls of the gall bladder during life permit the transudation of the bile, the current of blood in the small vessels, which chiefly constitute these walls, would carry off the bile as it becomes im- pregnated with it. But this cannot take place after death, as the circulation having ceased, there is nothing to carry off the infil- trated portion of bile. I have also frequently witnessed in living animals the imbibition and dislocation of the membranes from con- tact with colouring substances. If, for example, we inject into the pleura of a young dog a quantity of ink, in the course of an hour the pleura, pericardium, intercostal muscles, and even the surface of the heart itself, will become sensibly discoloured. This experi- ment is most striking in small animals, as rabbits, Guinea-pigs, mice, &c. It appears, then, placed beyond reasonable doubt that the walls of all the sanguineous vessels, arterial and venous, living and dead, large and small, possess a physical property quite adequate to ex- plain the principal phenomena of absorption. To affirm that this is the only property by which this process is effected, would be to transcend the limits of sound logic. In the present state of knowl- edge, I know of no fact which weakens this explanation, but, on the contrary, they all concur in sustaining it. Thus, Messrs. Lavoisier and Seguin have proved, by a series of interesting experiments, that the skin does not absorb water pr other substance, so long as it remains clothed with the epidermis. But the epidermis is not of the same nature as the vascular walls ; it is a sort of varnish which does not imbibe, as any one may observe in his own person when in a bath. But as soon as the epidermis is removed, the skin absorbs precisely like the other struc- tures, because the walls of its vessels are in immediate contact with the substances destined to be absorbed. Hence the necessity of placing under the epidermis the substances intended to be absorb- ed, as in vaccine inoculation; hence the necessity of prolonged frictions, and sometimes the use of unctuous substances, to promote the absorption of certain medicaments; hence our selection of that portion of integument where the epidermis is thinnest for ma- king these frictions. But under certain circumstances, the epidermis is capable of imbibition; this is daily witnessed from the application of cata- plasms, from which the cuticle becomes white, opaque, and thick. The imbibition most readily takes place from the external to the internal surface, as may be readily shown in the following manner. If we carefully remove the epidermis from one of the fingers and turn it inside out, and fill the cavity with water, and then close the opening by tying around it a piece of thread, the water will transude freely to the surface, and evaporate in a few hours. If, on the contrary, you leave the external surface on the outside, the VENOUS BLOOD. 379 water will evaporate very slowly, losing only a few grains of the water in twenty-four hours. It is upon this physiological fact, very simple in the present state of our knowledge, but which I have the satisfaction of having de- monstrated by the most unquestionable proofs, that the endermic method of using medicine is founded. It consists in removing the epidermis by a blister, and powdering the denuded surface with the substance that it is proposed should be absorbed. This pro- cess is often found very useful in modern therapeutics. I shall also cite the absorption of the most irritating substances, even those which are capable of acting chemically upon the tissues. This fact is entirely opposed to the idea that absorption is a purely vital action, and that there is a sort of election or choice exercised by the orifices of the absorbents. But it is no longer surprising, if we regard absorption as a physical property. It would be desirable to study this subject specially; to follow it in all the tissues, both during life and after death, as respects the different substances absorbed. Thus far, it has appeared to me that the serous membranes and cellular tissue, especially during life, probably in consequence of their high temperature, are the best agents of absorption. A drop of ink, for example, placed upon the peritoneum is immediately imbibed, spreading itself into a large round patch, which extends no deeper than the serous membrane. It requires some time to penetrate the subjacent tis- sues. A very important fact observed by my fellow-labourer, M. Fo- dere, is, that galvanism has a remarkable influence in accelerating the absorption, or, rather, imbibition. If prussiate of potash be in- jected into the pleura, and sulphate of iron into the abdomen of a living animal, under common circumstances it requires five or six minutes for these two substances to be brought in contact by im- bibition through the diaphragm. But the combination is almost instantaneous if the diaphragm be subjected to a slight galvanic current. The same phenomenon is observed if one of the liquids be placed in the urinary bladder, and the other in the abdomen, or in the lung and cavity of the pleura. The theory of absorption by the veins proposed by me has been confirmed in a remarkable manner by Doctor Bouillaud. In study* ing with attention partial oedema of the limbs, he found that there was more or less obliteration of the veins in the infiltrated part. Generally fibrinous coagula obstruct the vessels ; sometimes the veins are compressed by surrounding tumours. From some anal- ogous cases, M. Bouillaud was led to suppose that dropsies of the peritoneum arise from the difficulty of the passage of the blood through, the liver. Indeed, it is very rare that ascites of any con- siderable duration is not complicated with evident lesion of that organ. I opened the body of a man at the Hopital la Pitie who had died of a cancer of the liver. There was considerable ascites, according to the views of M. Bouillaud; there was also a large quantity of liquid in the small intestines. It might have been said 380 NUTRITIVE FUNCTIONS. that there was dropsy inside and out of that portion of the aliment- ary canal. I introduced a tube into the vena portae, and by this tube I forced an injection of water through the liver, the liquid passing without much difficulty into the right auricle. The liver, therefore, was not completely obstructed; but the disorganiza- tion was not very profound ; the tissue of the organ was easily recognised ; here and there only there were some traces of larda- ceous degeneration; the remainder of the parenchyma was gran- ulated, and yellow; the liver was turned upon itself, and of a bony consistence. I do not regard this fact as opposed to the explana- tion of M. Bouillaud, for the liver, though permeable to an injec- tion of warm water, may have ceased to be so, wholly or partial- ly, to the blood. Now, from experiments on absorption, it appears that a simple distention of the sanguineous vessels is sufficient to retard, or even prevent the absorption, or, in other words, the im- bibition of their walls. It may have been that the force with which the water was pushed through the liver in this case was much greater than that by which the blood was propelled through the vena portae. It must be admitted, that in every case a gener- al lesion of the liver, in which its structure is sensibly changed, cannot fail to act as an obstacle to the free circulation of the blood through that viscus. Passage of the Venous Blood through the Cavities of the Right Side of the Heart. If the heart of a living animal be exposed, we can readily per- ceive that the right auricle and ventricle contract and dilate alter- nately. These motions are so combined that the contraction of the auricle takes place at the moment when the ventricle is dila- ted, and vice versa; the contraction of the ventricle occurs at the moment of the dilatation of the auricle. Neither of these cavities is capable of being dilated without being at the same moment filled with blood, and when they contract a part of it is necessarily expelled. But such is the structure of the tricuspid and sigmoid valves, that the blood is compelled to pass successively from the auricle to the ventricle, and from this last to the pulmonary ar- tery. We will now enter into a detail of this curious mechanism. I have already observed that the blood contained in the three veins which terminate in the right auricle make a strong effort to penetrate into this cavity. If it be contracted, this effort is una- vailing ; but when a dilatation takes place the blood is precipitated into this cavity, fills it completely, and distends its walls slightly; it would penetrate into the ventricle if this cavity were not at the same moment in a state of contraction. The blood, then, is limit- ed precisely to filling at this moment the cavity of the auricle; but this soon contracts itself, and the blood, being compressed, must escape in that direction where the resistance is least. Now there are but two openings, the one towards the venee cavce, and the other in the direction of the ventricle. The sanguineous columns which arrive at the auricle oppose a certain resistance to its pas- VENOUS BLOOD. 381 sage in the first direction ; on the contrary, no obstacle exists to prevent its entrance into the ventricle, as, from its being dilated with force, it has a tendency to produce a vacuum, and thus to draw the blood from the auricle, instead of forcing it back. But in consequence of the thinness of the walls of the auricle it is in- capable of a sucking dilatation, as has been asserted by many physiologists. When observed in a living but empty heart, it con- tracts, and afterward becomes relaxed, but the latter is rather a passive than an active dilatation. In every instance this move- ment is too weak to draw the blood of the venae cavae by a pro- cess of sucking. On the contrary, the blood, by its impulsion, pen- etrates into the cavity of the auricle, and distends its watts. The action of the auricle, as I have observed, is sometimes entirely different. The contraction does not take place, its cavity remain- ing distended with blood ; at the moment that the right ventricle dilates to receive the blood, there is only a slight contraction of the auricle, chiefly dependant upon the elasticity of its walls. All the blood which passes from the auricle does not, however, enter the ventricle ; experiment has shown long since that, at each con- traction of the auricle, a certain quantity of this fluid flows back into the venae cavae. The undulation produced by this cause may be perceived as far as the external iliac and jugular veins; its in- fluence also upon the course of the blood is very sensible in sev- eral of the organs, especially the brain. The quantity of blood which flows back in this manner varies according to the facility with which this fluid is allowed to pene- trate into the ventricle. If, at the moment of its dilatation, the ven- tricle contain still much blood which has not passed into the pul- monary artery, it can, of course, receive but a small portion from the auricle, and its reflux will, therefore, be much more consider- able and extensive. This occurs when the blood in the pulmona- ry artery is retarded by obstacles placed in the substance of the lungs, or from the ventricle having lost its contractile power. The reflux of which we are speaking is the cause of the pulsation felt in the veins in certain diseases, and which has received the name of venous pulsation. Nothing of the kind occurs in the cor- onary vein, as its mouth is supplied with a valve which closes at the moment the auricle contracts. The instant the contraction of the auricle ceases, the ventricle contracts, by which the blood contained in it, being pressed on every side, endeavours to escape ; it would repass very easily into the auricle did no obstacle exist, as may be inferred from what we have already said, this cavity being then in a state of dilatation. But this is prevented by the action of the tricuspid valve, which is placed at the opening between the auricle and ventricle, and will not allow the reflux of the blood from the ventricle to the au- ricle. Pressed by the fluid with which the ventricle is distended, and which tends to pass into the auricle, this valve yields until it gets into a line perpendicular to the axis of the ventricle ; then its three divisions perfectly close the opening, and its fleshy and ten- 382 NUTRITIVE FUNCTIONS. dinous columns will not allow it to go any farther; this valve re- sists the effort of the blood, and prevents its passage into the au- ricle. But this is not the case with that portion of the blood which, during the dilatation of the ventricle, is placed on that side of the valve which corresponds to the auricle; it is evident that, when the valve is raised, this portion of the blood will be thrown back into the auricle, and mixed with that received from the venae cavae and coronary vein. Not being able to overcome the re- sistance of the tricuspid valve, the blood of the ventricle is com- pelled to enter into the pulmonary artery, into which it passes af- ter having pushed aside the sigmoid valves, which support the col- umn of blood contained in this artery, at the moment when the ventricle is dilated. The dilatation of the ventricle which succeeds its contraction is so energetic that it has been considered by many persons as active, and that it results from a particular vital property of the ventricular walls. I do not know of any plausible reason for ad- mitting this supposition, and cannot perceive why the dilatation of the ventricle should not be regarded as a simple return or re- laxation of the contracted fibres, arising from their elasticity. But whatever may be the cause of the dilatation of the ventri- cles, it is very intense; if you grasp the heart of a living ani- mal, you will be surprised at the extent of its dilatation. The ventricle then exerts a powerful absorbent or sucking action upon the blood contained in the auricle, which also, pressed by the force of its own impulsion, and the contraction of the auricle, pen- etrates suddenly into the cavity of the ventricle, and causes its rapid distention. The promptitude of the distention is such that it determines the shock of the anterior part of the ventricle against the sternum, and occasions a particular sound, easily distinguish- ed by the ear, and which merits the attention of the physician. This sound has been attributed, but without reason, sometimes to the contraction of the auricle, sometimes to the shock of the blood upon the walls of the ventricle at the moment of its entrance into this cavity. But these explanations of the sound of which we are speaking are erroneous; for if the heart be laid bare while in action, it does not produce any sound if the sternum be taken away or even raised. The sound will again return if the ster- num be replaced. We shall return to the consideration of this question when we speak of the contraction of the left ventricle. We will now proceed to explain the phenomena most appa- rent and best understood exhibited by the venous blood in passing through the right cavities of the heart; there are also other cir- cumstances which I conceive to be worthy of particular atten- tion. We should have but a very imperfect idea of this subject if we supposed that, in each contraction of the ventricle and auri- cle of the heart, these cavities emptied themselves completely of the blood which they contained. In observing the heart of a liv- ing animal, we distinctly see, at the moment of contraction, the auricle or ventricle become sensibly diminished in volume; but it VENOUS BLOOD. 383 is evident that, at the instant the contraction ceases, much blood still remains in the auricle or ventricle. There is only a part of the blood of the auricle which passes into the ventricle when it contracts. The same is true of the blood of the ventricle, a por- tion only of which passes into the pulmonary artery when the ventricle contracts ; these two cavities, therefore, are always filled with blood. What is the precise portion of blood displaced, it may be inquired, and how much remains ? They will vary, prob- ably, according to the force with which the ventricle and auricle contract, the facility with which the blood traverses the pulmo- nary artery, the quantity of blood contained in the auricle or ventricle, and the efforts made by the three sanguineous columns which empty into the auricle. The force of the blood when it reaches the auricle is some- times so considerable, that the latter cannot contract; it may re- main strongly distended for hours. It is only at the instant when the ventricle is relaxed that, in consequence of its elasticity, it re- acts a little upon itself This phenomenon occurs particularly at periods of great distention of the venous system. It affords a new proof that elasticity may replace contractility, and vice versa. In many diseases of the auricle the circulation must take place in this way. When the blood has arrived at the heart, it is continually agi- tated, pressed and beaten by the motions of this organ'; some- times it flows back into the venae cavae, or precipitates itself into the auricle ; again it passes with rapidity into the ventricle, is for- ced back suddenly into the auricle, and returns immediately after- ward into the ventricle; and again it penetrates into the pulmo- nary artery, and returns afterward into the ventricle, undergoing at each displacement a violent agitation.* Agitated and pressed in this manner with such prodigious force, the blood must under- go an intimate admixture of its constituent parts during the time it remains in the cavities of the heart and pulmonary artery. The chyle and lymph which the subclavian vein receives must be distributed equally in the blood of the two venae cavae. These two kinds of blood must also be compounded and completely uni- ted. I am almost tempted to believe, with Boerhaave, that the fleshy columns of the right cavities, independently of their uses in the contraction of these cavities, must have a considerable share in this agitation and admixture of the different elements of the blood. Indeed, the blood which is found in the auricle and ventricle not only occupies these large central cavities, but also the small cells formed by these columns.; of consequence, at each contraction it is forced partly into these cells, and is replaced at each dilatation by a new portion of blood. Being divided thus into a great num- ber of small masses, so as to occupy the cells when it is again united and expelled, it cannot fail, from the excessive agitation it * It is sufficient to touch but once the heart of a living animal to form an idea of the en- ergy of its contraction. 384 NUTRITIVE FUNCTIONS. suffers, that the different elements of which it is composed, which have a great tendency to separate, should become thus intimately blended and combined. For the same reason, the chyle, lymph, and drinks, which are carried by the veins to the heart, and that have not become intimately mixed with the blood, must undergo this change in traversing the right cavities of the heart. If we wish to form an idea of the influence of the right side of the heart, in this respect, we have only to force suddenly a quan- tity of air into the jugular vein of a dog, and examine the heart a few minutes afterward ; we shall see the air agitated and beaten about in the auricle and ventricle, forming a large mass of very fine froth. I have often observed these phenomena in living animals; and I have lately had an opportunity of confirming them upon a horse, the heart of the animal having been exposed by an incision on the lateral part of the thorax, and a section of one of the ribs. Passage of the Venous Blood through the Pulmonary Artery. Notwithstanding the numerous efforts of physiologists in inves- tigating the motion of the blood in the arteries, much still remains to be done on this subject. Experience and observation are here our only faithful guides ; our explanations must necessarily be im- perfect, as hydrostatics, the only science which can furnish them, has scarcely been extended to the motions of fluids in flexible tubes.* I shall not adopt the descriptions of other authors in giving an account of the motion and progress of the blood in the pulmonary artery. I prefer speaking of it at the moment when the relaxation of the right ventricle takes place, and to see after- ward what happens when the ventricle contracts, and forces the blood into the artery. This method appears to me to possess the advantage of placing this phenomenon in the most striking, point of view; its importance does not seem to me to be sufficiently ap- preciated. Let us .suppose the artery full of blood, and left to itself; the fluid will be pressed by the walls of the vessel through its whole extent, which will have a tendency to approach each other, and efface completely its cavity; the blood, being thus compressed, will endeavour to escape on every side. Now there are but two directions in which this can take place: the one is the orifice next to the heart; the other, the infinite number of delicate vessels in which the artery terminates in the tissue of the lung. The orifice of the pulmonary artery towards the heart being very large, the blood would be easily precipitated into the ventricle, if there did * I cannot resist quoting here the appropriate remarks of D'Alembert on this subject. " The mechanism of the human body, the velocity of the blood, and its action upon the ves- sels, cannot be reduced to a theory. We are ignorant of the precise action of the nerves, the elasticity of the vessels, their capacity, of the tenacity of the blood, and its different de- grees of heat. Were even these things known, the great multitude of other circumstances which would necessarily enter into such a theory would probably conduct us to calculations altogether impracticable. It is one of those cases of a compound problem, one of the most simple parts of which it would be extremely difficult to resolve. When the operations of nature are too complicated," adds this illustrious philosopher, " to enable us to submit them to our calculations, experiment is the only method that remains for us." VENOUS BLOOD. 385 not exist at this orifice a particular apparatus destined to prevent it. I allude to the three sigmoid valves. At the instant when the contraction of the ventricle forces the current of blood into the artery, these valves are brought in contact with the walls of the artery, and perpendicular to its axis; but the moment that the blood has a tendency to flow back in the ventricle, it places them in such a situation that they completely close up the cavity of this vessel. From the peculiar form of these valves, being that of a cul-de-sac, the. blood that enters into their cavity has a tendency to swell them out, and give a circular form to their fibres. This valve is divided into three portions, each of which is semicircular; now, if three semicircular bodies be brought together, there would necessarily exist a space between them. We might therefore suppose that the valves of the pulmonary artery, when they are pressed back by the blood, would leave a space by which the blood would flow back into the ventricle. It is undoubtedly true, that if each valve was single, it would assume a semicircular form; but as there are three, each acted upon by the blood at the same time, their sides are brought in contact with each other, and as they can each only be extended to a certain point, in consequence of the smallness of the space in which they are contained, they are therefore made to press each upon the other. The valves are therefore made to assume the form of a triangle, the apex of which is at the centre of the artery, and the sides in contact with each other, so as completely to intercept the cavity of the artery. Per- haps the small cartilaginous masses which exist at the apex of these triangles may be intended to close more accurately the ar- tery at its centre.* If we wish to see the manner in which these three valves are brought in contact with each other, it may be done in the follow- ing manner: if we inject gently wax, or prepared tallow, into the pulmonary artery, allowing it to pass from the ventricle, when the artery becomes filled the valves will be forced into, and brought in contact with each other; so that the orifice of the vessel will be closed with sufficient exactness to prevent a single drop of the injection from returning back into the ventricle. When the wax or tallow has become solid by cooling, we may examine, at our leisure, the manner in which the opening of the artery is closed up by the valves. The blood not being able, therefore, to flow back into the ventricle, will pass into the ramifications of the pul- monary veins, into which the small branches of the pulmonary artery are continued; and this will continue to be the case so long as the walls of the artery press with sufficient force upon the blood which they contain ; an effect which, with the exception of the trunk and principal branches, continues until the whole of the blood is expelled. It may be supposed that the fineness of the small vessels in which the pulmonary artery terminates acts as an obstacle to the blood. This would be the case if their number * See Sennac's Treatise on the Structure of the Heart Ccc 386 NUTRITIVE FUNCTIONS. were small, or if the sum of their diameters were less, or even equal to that of the trunk; but as they are innumerable, and as their aggregate capacity is much greater than that of the trunk, the current passes on with ease. It is, nevertheless, true that a state of distention or weakness of the lung renders this passage more or less easy, as will be more particularly shown hereafter. In order that the current of blood may pass with more facility, it is necessary that the power of contraction in the different di- visions of the artery should be in proportion to their size. If, for example, the action of the small vessels were superior to that of the large, while the first would expel the blood which they con- tained, they would not be distended by the blood coming from the second, and the fluid would therefore flow but very slowly. Now experiment shows that the contrary of this supposition is true. If the pulmonary artery of a living animal be tied immediately be- yond the heart, nearly all the blood contained in the artery when the ligature was made will pass promptly into the pulmonary veins, and arrive at the other side of the heart. We have now observed what happens when the blood con- tained in the pulmonary artery is exposed to the action of this ves- sel alone; but, in the ordinary state, at each contraction of the right ventricle, a certain portion of the blood is propelled with force into the artery; the valves are instantly raised; the artery, through the whole extent of its divisions, is distended in propor- tion to the force with which the heart contracts, and the quan- tity of blood which is thrown into it. Immediately after its con- traction the ventricle becomes dilated, and at this instant the walls of the artery react upon themselves; the sigmoid valves become depressed, and close the artery until a new contraction of the ven- tricle raises them. Such is the second cause of the motion of the blood in the artery which goes to the lungs ; they are, as we have seen, alternate ; let us endeavour to appreciate their effects. For this purpose, we will examine those phenomena which are most apparent in the course of the blood through the pulmonary artery. I have remarked, that at the moment when the ventricle forces the blood into the artery, its trunk and ramifications of a certain calibre undergo an evident dilatation. This phenomenon is called the pulsation of the artery. This pulsation is very strong near the heart, but grows weaker as you pass from it, and seems to cease altogether when the artery becomes very minutely subdi- vided. There is another phenomenon observed when we open the artery, which is a consequence of the preceding. If the opening be near the heart, and in a place where the pulsations are very distinct, the blood passes out in a jet, with a jerk; if the opening is made at a distance from the heart, and in a small branch of the artery, the jet is Continuous and uniform; lastly, if we open one of the very small vessels in which the artery terminates, the blood no longer passes out in a jet, but spreads itself in a uniform sheet. We see, in the first place, in these phenomena, a new application VENOUS BLOOD. 387 of the principle of hydrostatics quoted above, relative to the influ- ence which the size of the tube has upon the fluid which runs through it; the larger the tube, the less the velocity of the fluid passing through it. As the aggregate capacity of the ramifications of the artery increases as they approach towards the lungs, the velocity of the blood is necessarily diminished. With respect to the pulsation of the artery, and the jerk of the blood as it escapes from an opening in it, we see, evidently, that these two effects are the results of the contraction of the right ventricle, and the introduction of a certain quantity of blood into the artery, which is thus effected. Why are these two effects weakened at a distance from the heart, and why do they cease altogether in the last divisions of the artery ? It is not impossible, I think, to ^ive a satisfactory mechanical- reason for this. Suppose a cylindrical canal, of a given length, with elastic walls, and filled with a fluid ; if a new quantity of fluid be suddenly introduced into it, the pres- sure will be felt equally upon every point of the walls, which will be equally distended. Suppose, now, that this canal is divided into two parts, the sections of which, together, form a surface equal to that of a section of the main trunk of the canal; the dis- tention produced by the sudden introduction of a certain quantity of fluid will be less perceptible in the two divisions than in the trunk; because the total circumference of the two canals, being greater than that of the one canal alone, its resistance will be greater. If we suppose that these last two are divided and sub- divided indefinitely, the sum of the circumferences of the small tubes will be greatly superior to that of the great trunk; the same cause which will produce a sensible distention in the canal and its principal divisions will not be appreciable in the smallest sub- divisions, in consequence of the greater resistance of their walls.* This phenomenon will be still more remarkable, if the capacity of these divisions, instead of being equal, is greatly superior to that of the trunk. This last supposition is realized in the pulmonary artery, the capacity of which increases as it becomes divided and subdivi- ded. It is evident, therefore, that the effects of the introduction of a quantity of blood into this artery, at each contraction of the right ventricle, must diminish as it is propagated, and at last cease altogether in the last divisions of the vessel. It must not be for- gotten that the contraction of the right ventricle is the cause which keeps constantly in play the elasticity of the walls of the artery ; that is, which distends them so as to overcome the con- stant tendency which they have to approach towards each other, and expel the blood. From this it will be perceived that there is, * In order to understand this, it is necessary to recollect that the surfaces of circles are proportional to the squares of their circumferences. Thus, in the division of the canal into two branches, as we have supposed, if each circumference was only the half of the princi- pal canal, the surfaces of each of the secondary canals would be but the fourth part of the surface of the primitive canal, and these two surfaces united would form but the half of this canal; in order that they should be equal, therefore, it is necessary that the circum- ferences of the two divisions, taken together, should exceed the circumference of the prin- cipal canaL 388 NUTRITIVE FUNCTIONS. in fact, but one cause which gives motion to the blood in the pul- monary artery ; this is the contraction of the ventricle; that of the artery being but the effect of the distention that it undergoes at the instant when a certain quantity of blood penetrates into its cavity, being forced there by the ventricle. Authors have thought that they perceived in the contractions of the pulmonary artery, something analogous to that of the muscles. But when irritated with the point of an instrument, or caustics, or when submitted to the influence of a galvanic current, no mo- tion analogous to muscular contraction has ever been observed. We must, therefore, consider this contraction as an effect of the elasticity of the walls of the vessel. In order to estimate the importance of the elasticity of the walls of the artery, let us suppose, for an instant, that, with its dimensions and ordinary form, it became an inflexi- ble canal; immediately the course of the blood would be complete- ly changed. Instead of traversing the lungs in a continued stream, it would only enter the pulmonary veins at the moment that it was propelled forward by the ventricle ; at the same time it will be necessary to suppose that the artery would be always perfect- ly filled with blood; for if it were otherwise, it would be required that the ventricle should contract itself frequently before the blood would be made to pass into the lungs. Instead of this, observe what really takes place: the ventricle ceases for some moments to send blood into the artery; the course of the blood in the lungs nevertheless continues, as the artery contracts in proportion as it is emptied, and it requires that the time of emptying itself com- pletely should be passed over before the course of the blood into the lungs is completely stopped; now this suspension can never take place during life. The passage of the blood through the lungs is necessarily continued, and nearly equally rapid, whatever may be the quantity of blood thrown into the pulmonary artery at each contraction of the ventricle. Various attempts have been made to determine the quantity of blood thrown into the pulmonary artery at each contraction of the ventricle. In general, the estimate of its capacity has been form- ed on the supposition that all the blood it contains at the moment of its contraction passes into the artery; the estimate has been considerable. From what has been said above, however, it will be perceived how inaccurate this calculation must be, inasmuch as only a part of the blood contained in the ventricle is thrown into the artery; and as it is impossible to know how much is thrown out, and how much remains, it is evident that all these calculations give but an imperfect idea of the truth. Besides, it is much more important to know the mechanism by which the blood passes from the ventricle into the artery, and its course in this ves- sel ; the quantity of blood which passes in a given time, even if it were known^ would not be a circumstance of much importance. The blood, in passing from the small vessels in which the pulmo- nary artery terminates, and entering into the ramifications of the pulmonary veins, becomes changed in its nature in consequence RESPIRATION. 389 of the contact of the air, and acquires the peculiar qualities of the arterial blood. It is this change in the properties of the blood which essentially constitutes the function of respiration. CHAPTER XVI. ON RESPIRATION, OR THE TRANSFORMATION OF VENOUS INTO ARTE- RIAL BLOOD. It is an indispensable condition to our continued existence, that the blood should be constantly brought in contact with the air through a medium bearing a certain proportion in its extent to the superficies of the whole body. During this contact the air takes away from the blood certain of its elements, and, reciprocally, the blood seizes upon certain elements of the air. This constitutes respiration, or the transformation of venous into arterial blood. Some authors attach a different idea to respiration; it is often de- fined the introduction and discharge of air from the lungs, but this double motion may take place without the function of respiration being performed. Others have thought that it consisted in the passage of the blood through the lungs, but it often occurs that this is effected without respiration. To study successfully this function, we must have an exact knowledge of the structure of the lungs, and precise notions of the chemical. and physical properties of the atmospheric air; we must also understand by what mech- anism the air is made to penetrate into and pass out from the chest When we have described each of these points, we shall then consider the phenomenon of the transformation of venous into arterial blood. Of the Lungs. In the structure of the lungs, nature has resolved a mechanical problem of extreme difficulty. It has established an immense sur- face for the contact of the air with the blood in the very inconsid- erable space which the lungs occupy. This admirable contri- vance consists in an arrangement by which the minute vessels con- stituting the terminations of the pulmonary arteries, and the com- mencement of the pulmonary veins, are surrounded on all sides by air. Now the sum of the superficies of the walls of all the ca- pillaries of the lungs would be an extremely extensive surface. Here the blood is only separated from the air by the thin walls of the vessels in which it is contained. If these walls were imper- meable, as they would be if they were metallic plates, for exam- ple, the proximity of the air would be unavailable, and no chemi- cal reaction of the two bodies upon each other would take place. But all the membranes, particularly those that are very thin, are 390 NUTRITIVE FUNCTIONS. readily permeable to the gases, and even liquids, if they are not very viscid. Thus the walls of the pulmonary capillaries, though of sufficient thickness to retain all the viscid parts of the blood, offer but a slight obstacle to the passage of gas or the serosity of the blood. They are also readily traversed by the liquids or va- pours which are accidentally introduced into the lungs. It is not necessary to suppose, however, that the lungs, as re- gards respiration, possess special properties distinct from all the other organs ; for all the small vessels which contain venous blood, and which are in contact with the air, become the seat of the phe- nomenon of respiration. The lung is only much better arranged than any other organ for the production of this phenomenon. As respects their anatomy, the lungs are two spongy and vas- cular organs of considerable volume, situated on each side of the chest; their parenchyma is divided and subdivided into lobes and cells, the number, form, and dimensions of which are difficult to determine. From an attentive examination of a pulmonary cell, we learn that it is formed of a spongy tissue, the spaces of which are so small that it requires a glass of strong magnifying powers to see them distinctly ; these areoles communicate with each other, and are enveloped by a delicate cellular tissue, which separates them from the neighbouring cells. A portion of the bronchiae and pulmonary artery terminate about each of the cells. The artery is distributed about the tissue of the cells, but in a manner which is not known; it appears to terminate in an infinite number of minute ramifications in the pulmonary veins. I am myself dispo- sed to believe that these numerous small vessels in which the pul- monary artery terminates, and the veins commence, by crossing and anastomosing with each other in different ways, form the areoles.* The small divisions of the bronchiae which end about the cells do not penetrate into their in^rior, but finish suddenly when they arrive at the parenchyma. This last circumstance appears to me remarkable, for inasmuch as the bronchiae do not penetrate into the spongy tissue of the lungs, it is improbable that the surface of the cells with which the air is in contact is covered by the mucous membrane. Minute anatomy, at least, cannot demonstrate its existence in this place. A part of the eighth pair of nerves, and some filaments of the sympathetic, are distributed to the lungs, but we do not know pre- cisely how they are arranged. The external surface of the or- gan is covered by the pleura, a serous membrane analogous to the peritoneum both in structure and functions. About the bron- chiae, and near the place where they enter into the tissue of the lungs, there are a certain number of lymphatic glands, the colour of which is nearly black, and about which a small number of lymphatic vessels, which arise deep in the pulmonary tissue, ter- minate. The art of fine injections furnishes us with some information relative to the lungs, which must not be omitted. If we force an * This arrangement exists, more evidently, in the lungs of reptiles RESPIRATION. 391 injection of mercury, or simply of coloured water, into the pulmo- nary artery, the substance injected will pass into the pulmonary veins, and, at the same time, a part will penetrate into the bron- chia?, and pass out by the trachea. If the injection be made into the pulmonary veins, it passes into the pulmonary artery, and in part into the bronchiae. Again, if the injection be introduced through the trachea, we shall find that it penetrates into both the pulmonary artery and veins, and even into the bronchial ar- tery and vein. The lungs fill a great part of the cavity of the chest, enlarging and contracting with it; and as they communi- cate with the atmosphere by the trachea and larynx every time that the chest is enlarged, they are distended by the air, which is again expelled when the chest returns to its former dimensions. It is necessary, therefore, to stop a moment to examine this cav- ity. The chest or thorax is of a conoidal form, the apex of which is above, and the base below; posteriorly, it is formed by the dor- sal vertebrae; anteriorly, by the sternum; and laterally, by the ribs ; these last are twelve on each side, and are distinguished into true and false. There are seven of the first, and five of the last. The true ribs are above ; they are articulated posteriorly with the vertebrae; anteriorly they are articulated with the sternum, by means of a prolongation called the cartilages of the ribs. It is the length, disposition, and motion of the ribs upon the vertebrae, which determine the form and dimensions of the chest. The same muscle which, as we have already seen, constitutes the superior wall of the abdomen, forms also the inferior wall of the thorax. It is attached, at its circumference, to the lower part of the chest; but its centre is elevated towards this cavity, and forms, when it is in a state of relaxation, an arch, the middle part of which is on a level with the inferior extremity of the sternum. Thus the cavity of the thorax is divided into two portions, a su- perior, or thoracic, and an inferior, or abdominal portion. In the first, indeed, the thoracic organs, such as the heart, lungs, &c, only are lodged. The second contains the liver, spleen, and stom- ach. Numerous muscles are attached to the bones which form the outline of the thorax; of these muscles, some are intended to render the ribs less oblique upon the vertebral column, or to en- large the capacity of the chest; others depress the ribs, render them more oblique upon the vertebrae, and diminish thus the ca- pacity of the chest. It will be proper for us to investigate the mechanism by which the chest enlarges or contracts itself, many of the phenomena of respiration being immediately connected with these variations of capacity. The chest may be dilated vertically, transversely, and from before backward ; that is to say, in the directions of its prin- cipal diameters. The principal, or, to speak more correctly, the only agent of its vertical dilatation, is the diaphragm, which, in contracting itself, has a tendency to lose its arched form, and to become a plane; a motion which cannot be effected without the thoracic portion of the chest being increased, and the abdominal 392 NUTRITIVE FUNCTIONS. diminished. The sides of this muscle being fleshy, and corre- sponding to the lungs, descends more than the centre, which, be- ing aponeurotic, is incapable of jnaking any effort of itself, and is also retained by its attachment to the sternum, and its union with the pericardium. In most cases, this depression of the diaphragm is sufficient for the dilatation of the chest; but it sometimes hap- pens that the sternum and ribs, by changing the relation between them and the vertebral column, produce a sensible augmentation of the cavity of the thorax. Nothing is easier to conceive than the mechanism of this mo- tion when the physical arrangements of the part are well under- stood. It has, however, been a subject which has been discussed with great animation by some distinguished authors, who have, perhaps, given an importance to this question which it does not merit. If such controversies led to truth, we should not regret the time which the learned have devoted to them ; but it is rare that this is the result; at least, it has not happened as respects the mechanism of the dilatation of the thorax. After a great number of discussions and experiments apparently accurate, Haller's opin- ions, which appear to me far from satisfactory, have prevailed. I will explain myself upon this point with all the deference which so high an authority demands. His explanation of the dilatation of the thorax, now generally admitted, reposes upon bases which I cannot admit. He assumes that the first rib is nearly immovable,* and that the thorax is in- capable of any motion, as a whole, either above or below, f It is difficult to imagine how so acute an observer as Haller should have advanced and supported such an idea; for we have only to examine upon ourselves the motions of respiration in order to see that the sternum and first rib are elevated during inspiration, and depressed in expiration. The examination of the recent subject affords the same result; we have only to press the sternum supe- riorly, and it will be found, with all the sternal ribs, to yield; the first moves upon the vertebral column, and the thorax is consid- erably enlarged. After having assumed that the first rib is nearly immovable, Haller asserts that the second possesses five or six times more motion than the first; that the third is greater than the second; and that their mobility increases as you approach towards the lower ribs. With respect to the true ribs, the only ones which we are at present considering, I believe the fact to be directly the reverse of that advanced by Haller; that is, that the first rib is more movable than the second ; this, again, than the third ; and so on until you arrive at the seventh. But to judge accurately of the degree of mobility of the ribs, we must not confine ourselves to + Primum par (costarum) firmissimum est, inde ut quasque inferiori loco ponitur, ita facilius emovetur, donee infirma mobilissima fluctuet.—Haller, Elementa Physiohgia, torn, hi., p. 59, lib. viii. t Totum tamen pectus, ut nunquam elevari vidi, ita nunquam deprimi.—Haller, he. cit. RESPIRATION. 393 observing, at their extremities, the motions they execute. For as they are of unequal lengths, a slight motion in the articulation, when the rib is long, will appear very great in its extremity; in the same way an extensive motion in the articulation of a short rib would appear trifling, if examined at its extremity. It is neces- sary, therefore, in cosidering the motion of the ribs, to suppose them all of an equal length; if this be done, it will then be evi- dent that their mobility diminishes from the first towards the sev- enth, the last being nearly immovable. The anatomical arrangement of the posterior articulations oc- casions this difference of mobility. The first rib has but one ar- ticulating facette at its head, and is only attached to one verte- bra ; it has no internal ligament nor any costo-transverse liga- ment. The posterior ligament of the joint with the transverse apophysis, is horizontal, and cannot obstruct either the elevation or depression of the rib. None of these circumstances, which are so favourable to mo- tion, are found to exist about the other ribs; they have each two articulating facettes at their head, and are articulated with two ver- tebrae. They have an internal ligament in the articulation, which prevents a gliding motion; a costo-transverse ligament attached to the superior transverse apophysis, which prevents the rib from decending; a posterior ligament directed from below upward is seen behind the articulation of the tuberosity, and prevents the rib from rising. Different shades in the disposition of these dif- ferent ligaments permit the various degrees of mobility of which we have spoken. Besides, it is evident that a less degree of mo- bility existing in the long ribs, this is made up by the circumstance of their length, by which they are enabled to execute as exten- sive motions as the first, although they are less movable; for the- same reason, it is quite possible that they may exhibit even a greater extent of motion. This compensation is indispensable, as the true ribs, their cartilages, and the sternum can only move to- gether, and the motion of one of these pieces must, therefore, fol- low that of all the rest. It would follow, then, that if the infe- rior ribs were the most movable, they would be incapable of ex- ecuting a greater extent of motion than that of the superior; and the solidity of the thorax would be diminished without any advan- tage to its mobility. In most subjects, and frequently even in advanced age, the ster- num is composed of two pieces, articulated by a movable sym- phisis on a level with the cartilage of the second rib. This ar- rangement, by permitting the superior extremity of the inferior piece to project a little forward, assists in enlarging the chest in a manner which I think has never been remarked. But what are the muscles that elevate the sternum and ribs, and, of consequence, dilate the chest ? According to Haller, the intercostal muscles are the principal agents of this elevation. The first intercostals, he remarks, find a fixed point in the first rib, which is immovable, and elevate the second; and all the in- Ddd 394 NUTRITIVE FUNCTIONS. tercostal muscles successively taking the superior rib as their fix- ed point, elevate the inferior. But we have just seen that the first rib is far from being immovable; the explanation of Haller, therefore, necessarily falls to the ground; nor can I believe that the internal and external intercostals, whatever may have been said to the contrary, could produce the elevation of the ribs. The muscles which appear to me to be destined to this purpose are those which, having one extremity mediately or immediately at- tached to the vertebral column, the head, or superior extremities, can act directly or indirectly upon the thorax so as to elevate it Among these muscles I will cite the anterior and posterior sca- leni muscles, the muscles of the neck which are attached to the sternum, &c. I will also add another muscle, to which no one has ever attributed this use; I allude to the diaphragm. This muscle, indeed, is attached, at its circumference, to the inferior extremity of the sternum, the seventh true, and all the false ribs; when it contracts, it forces down the abdominal viscera, but, in order to do this, the sternum and ribs must present a resistance sufficient to counteract the effort made in the opposite direction. Now this resistance can be but imperfect, inasmuch as all these parts are movable ; for this reason, every time that the diaphragm contracts, it must elevate the thorax more or less. In general, the extent of the elevation will be in direct proportion to the re- sistance of the abdominal viscera, and the mobility of the ribs. There is another cause of the dilatation of the thorax, to which little attention has been heretofore given, but which appears to me to be very important. I refer to the pressure of the atmo- spheric air, which is exerted over the whole interior surface of the cavity, through the medium of the lungs. This pressure has such an influence, that if, by any cause, it ceases, the chest no longer dilates. The action of the elevator muscles on the ribs and the contraction of the diaphragm are ineffectual, if the thorax be not pressed upon internally by the atmospheric air. This phenom- enon is very remarkable in certain affections, as pneumonitis, oedema, and emphysema of the lungs, &c. Sometimes this occurs in the whole of one side of the thorax, and partly the opposite side; at others it is confined to three or four ribs on one side, the other ribs of the same side continuing to move. It is certain that the atmospheric pressure is much concerned in the dilatation of the thorax, inasmuch as, if it ceases to act for a certain time, the side which is deprived of it becomes contracted, occasioning a great change in the general conformation of the thorax. Another proof of this that may be mentioned is, the facility with which the chest may be dilated by blowing into the trachea in the dead body, and the difficulty experienced if we endeavour to dilate it by elevating the ribs and sternum. It is not indispensable that this pressure should be exerted through the medium of the lungs, as is proved by the following experiment Close with a ligature the trachea of an animal; it will immediately make impotent efforts to dilate the cavity of the RESPIRATION. 395 chest. Make then an opening in one of the intercostal spaces, when the air will immediately force itself into the open side of the chest, which will enlarge at each inspiration. Make an opening now on the opposite side, and you will observe the same effect. It will be remarked that the elevation of the ribs is more easy and complete than in ordinary respiration. The reason is sufficiently obvious: the pressure of the atmosphere is not through the medi- um of the lung, but directly upon the parts which it concurs in moving. In the general elevation of the thorax, the form of this cavity, and the relations of the bones which compose it, are necessarily •altered. The cartilages of the ribs appear to be peculiarly adapt- ed to this purpose. As soon as they become ossified, and, of con- sequence, lose their elasticity, the chest becomes immovable. At the same time that the sternum is carried superiorly, its inferior extremity is directed a little anteriorly; it experiences thus a slight oscillatory motion ; the ribs become less oblique to the ver- tebral column; and they separate a little the one from the other, the inferior edge being directed outward, in consequence of a slight inflexion which the cartilage undergoes. All these phenomena can only be distinctly observed-in the superior ribs; they are scarcely perceptible in the inferior. To judge accurately of the mechanism of inspiration, it is ne- cessary to study it in a person much emaciated, and under the age of thirty years. All the phenomena I have described will be vis- ible, but will become much more apparent if the individual be at- tacked with difficulty of respiration. Then all the forces which elevate the throat will appear in full action; the scaleni muscles will swell at each inspiration, and relax at every expiration. With respect to the intercostal muscles in laborious respiration, some- times they contract at the moment of inspiration, and sometimes, on the contrary, they relax when there is a remarkable depression in each intercostal space. There results from the elevation of the thorax a general en- largement of this cavity, both from before, backward, laterally, and from above downward. This enlargement is called inspira- tion ; it exhibits three well-marked degrees. First, ordinary in- spiration, which is made by the depression of the diaphragm, and an almost insensible elevation of the thorax. Second, a deep in- spiration, in which the elevation of the thorax is evident, at the same time that the diaphragm is depressed. Third, forced inspi- ration, in which the dimensions of the thorax are augmented in every direction that the physical disposition of this cavity will permit. In the first degree of inspiration, the air only penetrates into a limited portion of the lung; in the second, there is still more; but it is only in the third degree, forced inspiration, that it is introduced through the whole extent of the lung. This last mode of inspiration should be executed by the patient when we study the state of the respiratory organs. To the dilatation of the thorax succeeds expiration; that is, the return of the thorax to its 396 NUTRITIVE FUNCTIONS. ordinary position and dimensions. The mechanism of this mo- tion is precisely the reverse of that which we just described. It is produced by the elasticity of the cartilages and ligaments of the ribs, which tend to react upon themselves, when the relaxa- tion of those muscles which elevated the thorax permit it, and, finally, by the contraction of a great number of muscles, so dis- posed that they depress the thorax and draw it back. Among these muscles, which are very numerous and very strong, it is proper to mention the large muscles of the abdomen, the great dorsal, the sacro-lumbalis, and the serratus posticus inferior, &c. The contraction of the thorax, or expiration, presents also three degrees: first, ordinary expiration; second, deep expiration; third, • forced expiration. In ordinary expiration, the diaphragm, being relaxed, is crowded up by the abdominal viscera, which are press- ed by the anterior muscles of this cavity, and cause a diminution of the vertical diameter of the thorax. The relaxation of the in- spiratory, and a slight contraction of the expiratory muscles, per- mit the ribs and sternum to resume their ordinary relation to the vertebral column, and thus produce a strong expiration. But the retraction of the chest may go still farther than this. If the ab- dominal and other expiratory muscles contract forcibly, there will result from this a more remarkable crowding up-of the diaphragm, a much greater depression of the ribs, and a much stronger con- traction of the base of the chest, and, of consequence, a consider- able diminution of the capacity of the thorax. This is called forced expiration. To comprehend how the lung dilates and contracts with the thorax, Mayo compared the lung to a bladder on the interior of a bellows, which communicated with the external air through the tube of the instrument. This comparison, just in many respects, is inaccurate in one very important point of view. The bladder is an inert membrane, which suffers itself to be distended by the pressure of the air, but which does not return upon itself except by the compression of the walls of the bellows. The lung is in a very different condition; it is continually disposed to return upon itself, and to occupy a less space than the cavity it fills. It ex- erts, then, a traction at all points of the walls of the thorax. Thus traction has little influence upon the ribs, which cannot yield, but has a great influence upon the diaphragm. This muscle is always constantly drawn up by it so as to form an arch. When this muscle is depressed by contracting upon itself, it draws the lungs towards the base of the chest; these organs are more and more distended, and, in consequence of their elasticity, they are dispo- sed to react upon themselves, and to draw up the diaphragm with proportionate energy. The diaphragm, indeed, would be sudden- ly drawn back in the form of an arch as soon as it ceased to con- tract if it were not for a particular movement of the glottis, of which we shall speak below, and which opposes some obstruction to the sudden discharge of the air from the thorax. The ascen- sion of the diaphragm in expiration is also favoured by the elas- RESPIRATION. 397 ticity or even contraction of the abdominal muscles, which have been distended by the crowding down of the viscera at the mo- ment of the contraction of the diaphragm. To judge of this reciprocal action of the diaphragm and lung, it is necessary to lay bare the intercostal muscles on one side of the chest in a young animal, and see, through these muscles, the lung and diaphragm rise and descend together, without there be- ing any perceptible interval between them. We can also see that the lung is always in contact with the walls of the thorax, and that they glide upon these walls in their different movements. It is also easy to reritark that, during expiration, a great extent of the superior face of the diaphragm is applied to the walls of the thorax, and occupies the space that the lung filled during inspira- tion. Of the Air. The earth is surrounded on every side by a very thin and trans- parent fluid called the air, the whole mass of which is called the atmosphere. It extends from the surface of the earth to a height of about fifteen or sixteen leagues. The air is an elastic fluid; that is, it possesses in itself the property of exercising a pressure upon those bodies which it surrounds, and upon the walls of those vessels which contain it This property supposes, in the parti- cles of which the air is composed, a constant tendency to repel each other. Another property of the air is compressibility; that is, its volume changes according to the pressure to which it is submitted. Experiment informs us that the same mass of air, when subjected successively to different degrees of pressure, oc- cupies spaces or volumes which are in an inverse ratio to the de- grees of pressure; so that the pressure becoming double, triple, or quadruple, the volume is reduced one half, one third, or one fourth. In the atmosphere, the pressure that any given mass of air sup- ports is in proportion to the weight of those strata which are above it; its weight and density, therefore, diminish as .we rise from the earth. At the surface of the earth the pressure of the atmosphere is the result of its total weight. This pressure is ca- pable of sustaining a column of mercury thirty-two inches high; the instrument employed for this purpose is called a barometer. Different physical circumstances cause a slight variation in the atmospheric pressure. It is, for example, weaker at the summit of mountains than in valleys; it is greater when the air is char- ged with humidity than when it is dry. These variations may be very accurately appreciated by means of a barometer. Like all other bodies, the air is dilated by heat; its volume aug- ments 1.266 for every degree of heat of the centigrade thermom- eter. The air is heavy; this we may satisfy ourselves of by weighing at first a balloon filled with air, and weighing it after- ward, when it has been emptied by means of an airpump. It has been found in this way, the temperature being at 0, and when 398 NUTRITIVE FUNCTIONS. the barometer was raised to thirty inches, that sixteen cubic inches of air weighs 19 grains; the same volume of water weighed 2 pounds, 3 oz., 5 dr. Water is, therefore, 770 times heavier than air. The atmosphere is more or less charged with humidity; this arises from the continual evaporation of those waters which cover the surface of the earth. We find, from experiment, that water is changed into vapour at all temperatures, but this takes place most rapidly when the temperature is highest. Farther, the air can only contain a certain quantity of vapour at a given tempera- ture ; when it is saturated the humidity is extreme. The nearer it approaches this state the greater is the humidity; the instru- ments which indicate the humidity of the air are called hygrom- eters. When, in consequence of cooling, or any other cause, the air is incapable of containing all the vapour which it before pos- sessed, this excess assumes the form of mist or clouds, or is pre- cipitated in the form of rain, or snow, &c. The vapour of water being lighter than air, and causing it to become dilated when it is mixed with it, the result is, that humid is much lighter than dry air. Notwithstanding its thinness and transparency, the air refracts, intercepts, and reflects light. In a small mass, we see too few rays to have its colour produce a sensible impression upon our eyes ; in a large mass, the colour is very distinctly blue. The in- terposition of large masses of air gives also a bluish tint to distant objects. The air is of great importance in chemical phenomena. It was regarded for a long time as an element; its composition was first suspected by John Ray in the seventeenth century, and was afterward fully established by Lavoisier. The air is com- posed of two gases, possessing very different properties. First. Oxygen is a little heavier than atmospheric air, and combines with all simple bodies; it is one of the elementary principles of water, and vegetable and animal substances; and of the greater parts of known bodies, it is necessary to combustion and respira- tion. Second. Azote is rather lighter than air, is one of the ele- ments of ammonia and of animal substances, and extinguishes bodies in a state of combustion. The proportions of oxygen and azote which enter into the com- position of air are determined by means of instruments called eu- diometers. In these instruments we produce the combination of oxygen with some combustible body, such as hydrogen or phos- phorus, and the result of this combination makes us acquainted with the quantity of oxygen that the air contained. It is thus found that a hundred parts of air in weight contain 21 parts of oxygen and 78 of azote. The proportions are the same in all places and at all heights, and have not undergone any sensible change in the period which has elapsed since chemistry estab- lished this point in a positive manner. The air contains, besides oxygen, azote, and the vapour of water in a variable quantity, as we have already remarked, a very small quantity of carbonic RESPIRATION. 399 acid, the proportion of which is not fixed in a very rigorous man- ner. Nearly all combustible bodies decompose the air, at a tem- perature peculiar to each. In this decomposition, they combine with the oxygen, and leave the azote free. Inspiration and Expiration. The lungs are always filled with air, but this fluid is promptly altered by the act of respiration. It is therefore necessary that it should be frequently renewed; this is accomplished by the two phenomena of inspiration and expiration. In the first, the air is drawn into the lungs, distends them, and extends even to the ex- treme air-cells; during the second, a part of the air contained in the lungs is driven out. In these two physical acts the atmo- spheric pressure and the muscular contraction are the principal agents. If we examine the chest after an ordinary expiration, we see that the air which presses upon its external surface is exactly in equilibrio with that which presses upon the internal surface of the lung. The pressure of the latter occurs through the medium of the column of air in the cavity of the mouth and nasal passages, the pharynx, larynx, trachea, and bronchiae. The least effort of the powers which dilate or contract the thorax will be suffi- cient to cause the air either to penetrate into the lungs, or expel it. The mechanism of respiration is therefore easy; as soon as the dilating muscles of the thorax act, immediately the external air is precipitated into the glottis, the trachea and the lungs are filled, as the tendency to a vacuum is produced by the enlargement of the chest. We may here make a few remarks in explanation of the hard- ness and elasticity of the walls of the passage through which the air passes to arrive at the air-cells of the lungs. Let us sup- pose, for a moment, that the walls of the trachea or larynx had been membranous instead of cartilaginous; then, at the moment of the dilatation of the thorax, the air, which presses equally on all points of the surface of the body, would close up the aerial passa- ges about the neck, and the air could not penetrate into the tho- rax. But the walls of the mouth, nose, and larynx, and the rings of the trachea, resist the pressure of the air, which can only act upon the internal surface of the air-passages. There is such a relation between the pressure of the atmosphere and the cartilaginous aerial passages, that where there is no pres- sure, as on the posterior part of the trachea and the small bron- chial divisions, there is no cartilaginous structure. If we recollect the disposition of the pulmonary cells, the ex- tensibility of their tissue, their communication with the external air by means of the bronchiae, the trachea, and the larynx, we shall be easily able to conceive that every time the chest is dilated the air rushes into the lungs in a quantity proportioned to the degree of dilatation. When the chest contracts itself, a part of the air contained in it is expelled, and rushes out through the glottis. In 400 NUTRITIVE FUNCTIONS. order that the air may arrive at the glottis in inspiration, or pass out from it in expiration, it will sometimes traverse the nasal fos- sae, and sometimes the mouth; the position that the veil of the palate assumes on these occasions deserves attention. When the air traverses the nasal fossae and the pharynx, to enter into the larynx, or to pass out from it, the veil of the palate is vertical, and applied to the anterior surface of the posterior part of the base of the.tongue, so that the mouth has no communication with the pharynx. When the air traverses the mouth, in inspiration or expiration, the veil of the palate is horizontal, its posterior edge embraces the concave surface of the pharynx, and all communica- tion is stopped between the inferior part of the pharynx and the superior part of this canal, as well as the nasal fossae. Hence the necessity of requesting patients to breathe through the mouth, if we wish to inspect the tonsils or the pharynx. These two ways by which air arrives at the glottis are neces- sary, and occasionally supply each other's place. Thus, when the mouth is filled with aliment, the respiration is made through the nose; and it takes place through the mouth when the nasal fossae are obstructed by mucus, a slight swelling of the pituitary membrane, or any other cause. The glottis is by no means passive during inspiration and ex- piration. It opens and closes alternately. Its dilatation, which co- incides with inspiration, favours the entrance of the air into the respiratory organs. The closing takes place at the moment that expiration begins, so that it always presents a certain obstacle to the expulsion of the air from the lungs, and its edges are always moved by the expired air. By completely closing the glottis we can entirely prevent the expulsion of the air, whatever may be the expiratory effort. In this case the small constrictor muscles of the glottis resist the immense powers concerned in expiration. Some diseases appear to consist principally in defective dilatation of the glottis during inspiration ; the consequence is extreme dysp- noea, with the most violent efforts to drive the air into the lungs. I had a striking example of this in a child on whom I performed the operation of laryngotomy. I was led to believe that the suf- focation arose from a false membrane that closed up the glottis. As soon as the operation was performed, the air entered the lungs freely through the wound, and the sense of imminent suffocation at once ceased, which proved that the obstacle was about the glottis. Still it was found without obstruction. I then attempt- ed to close the wound, and make the child breathe through the larynx; but the suffocation immediately returned, so that I was compelled to keep the edges of the incision open for twenty-four hours by an assistant It appears that the number of inspirations made in a given time differs essentially in different individuals. Hale states that there were twenty in the space of a minute. A man upon whom Men- zies experimented, breathed but fourteen times in a minute. Sir Humphrey Davy informs us that he respired twenty-six or twen- RESPIRATION. 401 ty-seven times in that space. Mr. Thompson says that his ordi- nary breathing is nineteen times in a minute ; but I breathe my- self fifteen times in the same period. Taking twenty, then, as the medium, we shall have 28,800 inspirations in twenty-four hours. But it is probable that this number will vary very much, from a variety of circumstances: such as the duration of sleep, motion, distention of the stomach by aliment, the capacity of the chest, and the moral affections. What quantity of air, it may be inquired, enters into the chest at each inspiration ? What quantity passes out at each expira- tion ? And how much remains there habitually ? According to Menzies, the medium quantity of air which enters into the lungs at each inspiration is three hundred and twenty cubic inches. Goodwin thinks that, after a complete expiration, the lungs still contain about eight hundred and eighty cubic inches. Menzies asserts that the quantity is much greater, and that it amounts to fourteen hundred and sixty-one cubic inches. According to Davy, after one strong expiration, his lungs re- tain three hundred and thirty-two cubic inches. After a natural expiration . . . 970 cub. in. After a natural inspiration . . .1106 " After a strong inspiration . . . 3206 " By strong expiration, after a deep inspi- ration, there passed out from the lungs . 1556 " After a natural inspiration . . . 643 " After a natural expiration . . . 353 " Mr. Thompson thinks that we shall not be far from the truth if we suppose the quantity of air generally contained in the lungs to be 2294 cub. in., and that there enters and passes out of the chest, at each expiration and inspiration, 327 cub. in. Thus, sup- posing twenty inspirations in a minute, we should have entering and passing out from the lungs in this time 6500 cub. in.; and in twenty-four hours 75,556 cub. in., or nearly 48 pounds. Chemists have made a great number of experiments to deter- mine whether the volume of air diminishes during the time it re- mains in the lungs. The most recent experiments, those of Messrs. Dulong and Despretz, show the diminution to be considerable. M. Despretz, having caused six small rabbits to breathe in forty- nine pints of air, during two hours, found there was a diminution of one pint. In traversing successively the mouth or nasal cavities, the pharynx, the larynx, the trachea, and the bronchiae, the inspired air acquires a temperature nearly equal to that of the body. Hav- ing become heated, and, of consequence, rarefied, the same quan- tity of air in weight occupies a much greater space in the lungs than before it was introduced into this viscus. Besides this change in volume, the inspired air becomes loaded with the va- pour which is continually thrown off from the mucous membrane of the lungs; it is therefore not only warm, but humid, when it E E E 402 NUTRITIVE FUNCTIONS. arrives at the pulmonary cells ; finally, the portion of air of which we have spoken becomes mixed "with that which the lungs before contained. But expiration soon succeeds inspiration ; a few sec- onds ordinarily intervene; the air that the lungs contain, com- pressed by the expiratory powers, escapes in an inverse ratio to the air inspired. It is proper here to remark, that the portion of air expired is not identically that which had been just inspired, but is a portion of the mass which the lungs contained before in- spiration. If we compare the volume of air that the lungs habit- ually contain with that inspired and expired at each respiration, we shall be induced to believe that the end of inspiration and ex- piration is but to renew, in part, the large mass of air contained in the lungs. This renewal will be much more considerable when the quantity of air expired is very great, and the succeeding inspiration strong. Physical and Chemical Changes that the Air undergoes in the Lungs. The air passes out from the lungs at about the same temperature with the body; a great quantity of vapour, called pulmonary transpiration, escapes with it; its chemical composition is differ- ent from that of the air inspired. The proportion of azote is nearly the same, but the quantity of oxygen and carbonic acid are essentially different. Instead of twenty-one parts of oxygen, and one of carbonic acid, in one hundred, which the atmospheric air presents, the expired air is found to contain eighteen or nine- teen parts of oxygen and three or four of carbonic acid. In gen- eral, the quantity of carbonic acid is less than that of the oxygen that has disappeared. From the late experiments of Messrs. Du- long and Despretz, this difference is about one third in carnivo- rous animals, and only about one tenth in herbivorous. To esti- mate the quantity of oxygen consumed by an adult in twenty-four hours, it is only necessary to recollect the quantity of air respired during this interval. According to Lavoisier and Davy, two hundred and fifty-six cubic inches are consumed in one minute, which gives in twenty-four hours two thousand nine hundred and eighty cubic inches. It is not difficult to appreciate the quantity of carbonic acid that passes out from the lungs at the same time, inasmuch as it is near- ly equal to the volume of oxygen that has disappeared. Thomp- son estimated it at three hundred and twenty cubic inches; though it may be, he remarks, probably less. Now this quantity of car- bonic acid represents about five thousand two hundred and sev- enty grains of carbon. Some chemists say that a small quantity of azote disappears during respiration; but this has not been con- firmed by the most recent researches. Others have thought, on the contrary, that the quantity of this gas is sensibly augmented. This last result has been placed beyond doubt by the labours of Messrs. Edwards, Dulong, and Despretz, who have always found a decided increase of azote in the air when respired by animals RESPIRATION. 403 after a certain time. We are informed of the degree of alteration that the air undergoes in our lungs by a sensation which impels us to renew it. This is hardly perceptible in common respira- tion, because we hasten to obey this impulse; but it becomes ex- tremely painful if this sensation be not satisfied; it soon causes anxiety and fear, which are instinctive evidences of the impor- tance of respiration. While the air contained in the lungs is thus modified, both in its physical and chemical properties, the venous blood traverses the ramifications of the pulmonary artery, which form, in part, the tissue of the cells of the lungs. It then passes into the ramifications of the pulmonary veins, and soon into the veins themselves; during this, the nature of the blood becomes changed from venous to arterial blood. Let us now examine the phenomena of this transformation. Change of the Venous into Arterial Blood. At the moment when the blood passes through the minute ves- sels which cover the pulmonary or air cells, it assumes a bright scarlet colour; its odour is stronger, its taste more distinct, and its temperature elevated about one degree. One part of the se- rum escapes, in the form of vapour, into the air-cells, and mixes with the air. Its tendency to coagulate sensibly augments. This fact is generally expressed by saying its plasticiU is much great- er ; its specific gravity, and its capacity for caloric, are both di- minished. When the venous blood has acquired these charac- ters, it becomes arterial. In order that we may render more ev- ident the differences between arterial and venous blood, we shall recapitulate them in the following table: Principal Differences between Venous and Arterial Blood. Venous Blood. Arterial Blood. Colour . . .a modena red, bright scarlet. Odour .... weak, strong. Temperature . . 98° Far. nearly 100. Capacity for caloric . 852,* 839. Specific gravity . . 1051,* 1049. Coagulation . . less prompt, more prompt. Serum . . . more abundant, less abundant. An analysis of the venous and arterial blood by Messrs. Ma- caire and Marcel has enabled them to point out a striking differ- ence between these two liquids, especially as regards the quantity of oxygen and carbon that enters into their composition. The following is the result of their analysis made by the oxide of cop- per after having dried the blood in a vacuum by sulphuric acid, and reduced the arterial blood to a beautiful red powder, and the' venous to a reddish brown. Arterial Blood. Venous Blood. Carbon .....50.2 55.7 Azote . .....16.3 16.2 Hydrogen Oxygen .....6.6 .....26.3 * Water being as 1000.—J. Davy. 6.4 21.7 404 NUTRITIVE FUNCTIONS. I have already described the changes that the air undergoes in the lungs, and am now about to notice those which take place in the venous blood in traversing these organs; let us now see what connexion exists between these two orders of phenomena. The colour of the blood evidently depends upon its mediate con- tact with the oxygen; for, if any other gas exists in the lungs, or if the atmospheric air be not renewed, this change in colour no longer takes place. But it manifests itself anew as soon as we permit the introduction of oxygen gas into the air-cells of the lungs. It is easy to see the phenomenon of the change in colour of the venous blood, even in the dead subject. At the approach of death, the venous blood often accumulates in the vessels of the lungs ; the bronchiae being deprived of air, it preserves the venous properties long after death. If the atmospheric air be forced into the trachea in such a manner as to distend the tissue of the lungs, it causes a change of colour in the blood, from the modena red to a bright vermilion tint. The same phenomenon is observed whenever the venous blood is brought in contact with oxygen or atmospheric air. Blood drawn from a vein and exposed to the air assumes a brighter tint; immediate contact is not necessary; the same blood con- tained in a bladder, and plunged into oxygen gas, becomes scar- let over its whole surface. Thus the very delicate vascular walls which, in the lungs, separate the atmospheric air and the blood, cannot be considered as an obstacle to this change of colour. But it may be inquired, How does oxygen gas produce this change of colour in the venous blood ? Chemists are not agreed upon this point. Some think that it combines directly with the blood ; others, that it removes from the blood a certain quantity of car- bon ; and there are others, again, who are inclined to believe that both these effects take place ; but neither of these explanations will satisfactorily account for the change of colour. Many chem- ists have attributed the peculiar colour of the blood to the pres- ence of iron, but this opinion is now rejected as extremely doubt- ful ; it will, however, seem less unreasonable, when it is recollect- ed that if this metal be separated from the coloured part of the blood, it loses the property of becoming scarlet on being exposed to oxygen gas.* We may easily imagine the loss of serum which the blood un- dergoes in respiration. It is very probable that a certain quantity of serum escapes from the extreme ramifications of the pulmonary artery, and evaporates into the air which the cells contain. This vapour afterward passes out with the expired air, under the de- nomination of pulmonary transpiration; but it does not necessari- ly follow that all the vapour which passes out from the blood du- ring expiration arises from the pulmonary artery. I have re- marked above, that a considerable portion of this vapour is thrown * We must not confound the colouring matter of the blood described by Messrs. Brande and Vauquelin with hcematine, the colouring matter of logwood, which was dis- covered by M. Chevreul. RESPIRATION. 405 off by the arterial blood, which is distributed to the mucous mem- brane of the bronchiae. In his first researches upon respiration, Lavoisier believed that a combination of hydrogen and oxygen took place in the lungs, from which resulted the formation of a Certain quantity of water; and that this water formed a part of the pulmonary transpiration. This idea, however, is not at pres- ent admitted; but this transpiration is considered as the result of the passage into the air-cells of a part of the fluid which passes through the pulmonary artery. Anatomy seems to confirm this; water injected into the pulmonary artery passes, under the form of innumerable small drops, almost imperceptible, into the air- cells, and mixes with the air which they contain. In living animals we may increase at will the quantity of pul- monary transpiration, by injecting distilled water at, the tempera- ture of the body, into the venous system, as the following experi- ment will prove. Take a small dog, and inject, at different times, a considerable volume of water; the animal will at first be in a perfect state of plethora; its vessels will be so completely distend- ed, that it will move with difficulty; but, at the end of some mo- ments, its respiration will become considerably accelerated, and there will be poured out a great abundance of fluid from the throat, the source of which is evidently the pulmonary transpira- tion considerably augmented. It is not only the aqueous part of the blood which escapes by pulmonary transpiration. I have shown, by direct experiments, that many substances introduced into the veins, either by absorption or direct injection, soon pass out by the lungs. Diluted alcohol, a solution of camphor, of aether, or odoriferous substances, introduced into the cavity of the peri- toneum, or any other part, are soon absorbed by the veins, and, transported to the lungs, pass into the bronchiae, and may be rec- ognised by the peculiar odour of the expired air. Phosphorus acts in the same manner; its odour is not only sen- sible in the expired air, but its presence is still more easily shown, and in the most positive manner. Inject into the crural vein of a dog half an ounce of oil, in which phosphorus has been dissolved; you will scarcely have performed this operation, when there will issue from the nostrils of the animal a dense white vapour, which is the phosphoric acid. It appears from the experiments of Dr. Nysten, that gases act in nearly the same manner; that is, that after they have been injected into the veins, they pass out with the expired air. Some attempts have been made to determine the quantity of vapour that escapes from the lungs of an adult in twenty-four hours. The latest, performed by Mr. Thompson, fix it at about eighteen ounces; Lavoisier and Seguin formerly estimated it at something less than this. It is probable that it is varied by an infinite number of circumstances. It is not yet considered as settled in what mode the carbonic acid contained in the expired air is formed. It is thought by some that it exists, ready formed, in the venous blood, and that 406 NUTRITIVE FUNCTIONS. it is exhaled by this fluid at the moment of its passage through the lungs; by others, that it is the result of the direct combi- nation of the carbon of the venous blood with the oxygen; but neither of these opinions can be considered as fully established; perhaps both these effects may take place at the same time. From our ignorance of the mode of formation of the carbonic acid, we are unable to fix the precise part performed by the oxy- gen in respiration. Some assert that it is employed to combine with the carbon of the venous blood; others, that it passes into the pulmonary veins; and there is still another class who believe that it performs both these offices at the same time. All this part of animal chemistry requires farther investigation; so long as we have not any positive knowledge concerning the formation of carbonic acid, and the disappearance of oxygen, it will be dif- ficult to determine the cause of the elevation of temperature which takes place in the blood in passing through the lungs. It is prob- able, however, that the oxygen combines with the carbon of the blood, and, as every formation of this kind is accompanied by a considerable evolution of caloric, it is probable that this is the cause of the increased heat of the arterial blood. If we suppose, also, that the oxygen is absorbed, passes into the pulmonary veins, and that it combines afterward directly with the blood, we may then account for the elevation in the temperature of the blood; for every combination of oxygen with a combustible body is ac- companied with an evolution of caloric* The slight diminution in the specific gravity of the blood, and its capacity for heat, arises probably from the loss of water from the surface of the air-cells. With respect to the other properties that the venous blood acquires in traversing the lungs, such as its odour, peculiarity of taste, &c, that our opinions on this point may be accurate, it is necessary that an exact and comparative analysis of the venous and arterial blood should make us precise- ly acquainted with these differences. This is a service for which physiology looks to the science of chemistry. Respiration of other Gases than Atmospheric Air. We must not rest satisfied with studying the effects of the res- piration of atmospheric air; we are naturally desirous of knowing what would be the result of the respiration of other kinds of gas. Animals have been plunged into them, and men have voluntarily or involuntarily respired them; it is thus known that atmospheric air alone can serve the purposes of respiration for any consider- able time. Every other gas destroys animal life more or less promptly; oxygen itself, when respired pure, is fatal, and even when it is mixed with azote in proportions different from the com- mon air, it sooner or later causes the death of those animals that respire it. From these facts we are induced to divide gases, as they relate to respiration, into two classes: first, those which are non-respirable; second, those that are deleterious. * See article Animal Heat. RESPIRATION. 407 The first, to which belong the protoxide of azote, hydrogen, &c, destroys animals only because they are incapable of fulfilling the office of oxygen. Among these gases there is one, the pro- toxide of azote or nitrous oxide, which produces very remarkable effects, and which may perhaps be considered as belonging to the second class. Sir H. Davy was the first who examined the ef- fects of this upon himself. After having expired the air from his lungs, he breathed about five pounds of the protoxide of nitrogen; the first sensations which he experienced were those of vertigo; at the end of about half a minute, continuing still to respire this air, these effects gradually diminished, and were succeeded by a sensation analogous to a gentle pressure over all the muscles, ac- companied by a slight, but very agreeable trembling, particularly in the chest and extremities. Surrounding objects appeared to him of a dazzling brightness, and his hearing to become more acute ; towards the last, the agitation augmented, his muscular force seemed much increased, and he felt an irresistible propen- sity to put himself in motion. These effects diminished as soon as he had ceased to respire the gas, and in the course of ten min- utes he found himself as usual. . The effects are not however, always the same; Vauquelin and Thenard, who also respired this gas, did not perceive all the phe- nomena described by Davy, but others analogous to them. The deleterious gases are those which are not only incapable of respi- ration, but destroy, more or less rapidly, men and animals which respire them, even when mixed with certain portions of atmo- spheric air. Of this number are all the acid gases, ammoniacal gas, sulphuretted hydrogen, &c, &c. Influence of the Nerves of the Eighth Pair upon Respiration. The nerves of the eighth pair are the only cerebral nerves which send filaments to the tissue of the lungs; this has induced physiologists to divide them, to ascertain the effects that would result from it. This easy experiment was made often by the older physiologists, and there are few of the modern who have not re- peated it. Every animal in which the nerves in question are di- vided dies more or less suddenly; sometimes death takes place instantly after the division. It never survives more than three or four days. Death has been attributed by authors, in turn, to the cessation of the motions of the heart, imperfect digestion, inflam- mation of the lungs, &c. We are indebted to the labours of many physiologists, and especially to Messrs. Wilson, Philip, and Bres- chet, for some valuable information on this subject. I now pro- pose to give an abstract of their researches and my own. A division of the nerves of the eighth pair, in the neck, on a level with the thyroid gland, or even lower, has an influence, first, upon the larynx; second, upon the lungs. These two classes of effects must be distinguished. In treating of the voice, we have said that the division of the recurrent nerves produced a sudden loss of the voice. The same phenomenon takes place after the 408 NUTRITIVE FUNCTIONS. division of the eighth pair of nerves, which is easy to understand, as the recurrents are but branches of these nerves. But, besides the loss of the voice, it is not uncommon for a section of the nerves of the eighth pair to be followed by such an approximation of the lips of the glottis, that the air is incapable of penetrating into the larynx, and that sudden death happens; as is always the case in an animal which is incapable of renewing the air of its lungs. In ordinary cases, the sides of the glottis are not brought so ex- actly in contact as to entirely prevent the air from entering into the larynx for the purposes of respiration. But, as the glottis has lost its peculiar motion, the air enters into, and passes out from the chest, in a more irregular and constrained manner. At the time when these observations were made, it would have been impossible to have explained satisfactorily these different phenomena. But as the readert is now acquainted with the man- ner in which the recurrent and laryngeal nerves are distributed to the muscles of the larynx, the subject presents no farther diffi- culty. By the division of the eighth pair at the lower part of the neck, the dilator muscles of the glottis are paralyzed. This open- ing no longer enlarges itself at the instant of inspiration, while the constrictors, which receive their nerves from the superior laryn- geal, preserve their action, and close the glottis more or less com- pletely. When the section of the eighth pair is not followed by such a constriction of the glottis as to cause instantaneous death, other phenomena are developed, and death does not occur until the end of three or four days. Respiration is at first constrained, the motion of inspiration is more extensive and frequent, and the animal seems to pay a par- ticular attention to it; he is not inclined to move, is evidently fa- tigued by exertion, and will often preserve a perfect state of re- pose. The formation of arterial blood is not prevented for a short time after the operation; but soon, the second day, for example, the laborious respiration increases, and the efforts in inspiration become greater. The arterial blood has no longer the vermilion tint which is peculiar to it; it becomes deeper coloured, and its temperature diminished ; at last all these symptoms increase ; res- piration can only be effected by the action of all the inspiratory muscles; the arterial blood becomes of a dull red, and similar to venous blood; the arteries containing but little of it, a chilliness becomes manifest, and the animal soon dies. On opening the chest we find the bronchiae, and sometimes the trachea itself, fill- ed with a frothy fluid, sometimes bloody; the tissue of the lungs is engorged and swollen; the ramifications, and even the trunk, of the pulmonary artery, are distended with blood of nearly a black colour; there is likewise found a considerable effusion of se- rosity, or even of blood, into the parenchyma of the lungs. On the other hand, experiments show that, in proportion as this se- ries of phenomena becomes developed, the animals consume less oxygen, and form a less quantity of carbonic acid. It has been supposed, with reason, that in this case the animals perish be- RESPIRATION. 409 cause respiration cannot be performed, the structure of the lungs being so altered that the inspired air cannot arrive at the air-cells. I think we may add to this cause the difficulty which the blood from the pulmonary artery experiences in passing into the vein; a difficulty which appears to me to be the cause of the distention of the venous system after death, and of the small quantity of blood which the arterial system contains some time before this event happens. The section of one of the nerves of the eighth pair produces these effects upon one of the lungs only, and life may be contin- ued by the action of the other of these organs, the animal not per- ishing. I have seen animals live in this state many months. Many authors, worthy of confidence, have stated facts respect- ing the division of these nerves that I have not been able to ver- ify. If we allow an interval of a month or two, say they, be- tween the division of one nerve and that of the second, the ani- mal survives, a union taking place between the divided ends, and that cicatrix transmits the nervous influence like the nerve itself. Cut this cicatrix, divide the nerve a second time, and at the same moment the effects of the simultaneous section of the two nerves will become manifest. I will not pretend to deny these results, but I have endeavoured to repeat them without success. I have cut, in dogs, the eighth pair on one side; three months after I have cut that of the opposite side; the animals died three or four days after the last operation. At the opening, after death, I have found the lung on the side on which the first nerve was cut so changed in its structure that it was incapable of the function of respiration. Hence the division of the second nerve necessarily caused death. According to some physiologists, the simple division of the eighth pair differs much, as respects the results, from a section where a certain portion of the nerve is cut away so as to leave a considerable interval between the divided ends. In general, say they, the effects are much more striking, and the animals die much sooner. It is the same if, instead of cutting off a portion of the nerve, we fold away one of the ends so that it shall be remote from the other. Lastly, here, as in indigestion, it'is said that a galvanic current takes the place of nervous influence. My ex- periments do not agree with these results. I have never seen any difference, as regards the results, be- tween the simple division of a nerve or cutting off a portion. I have never obtained anything, in these circumstances, from the galvanic action. Of Artificial Respiration. The principal object of the motion of the thorax is to draw air into the lungs, and afterward to expel it from these organs. Whenever these motions are stopped, the air of the lungs being no longer renewed, respiration necessarily ceases, and death soon follows. But we may supply, for a certain time, the action of 410 NUTRITIVE FUNCTIONS. the thorax, by introducing air artificially into the lungs. Both an- cient and modern anatomists have often practised this. The air has been gradually introduced with bellows, or bladders, &c. This may also be done with a syringe, with a small hole on the side of its tube. The end of the tube is introduced into the tra- chea, and fixed there by a ligature; afterward we draw the pis- ton, in order to fill the syringe with air ; we then apply one finger upon this small hole, to prevent the air from passing out through it; the piston is then forced down, and the air of the syringe passes into the lungs. We then withdraw the piston, and the syr- inge becomes filled with air from the lungs; we now raise the finger placed upon the small hole, and, by pushing down the pis- ton, cause the air to escape, which has already performed the pur- poses of respiration; we draw immediately the piston, to fill the instrument with pure air, leaving the little hole open, &c. By repeating regularly these motions, we are enabled to protract the life of an animal, in which the thorax has become immovable, either from a division of the spinal marrow behind the occipital bone, or even where the head has been entirely cut off. It, how- ever, fulfils but very imperfectly the function of respiration, and can never be prolonged beyond a few hours. Frequently the lungs become engorged by the blood, or are torn by the air; this fluid is also introduced into the pulmonary veins, and spreads itself into the cellular tissue, so as to prevent the dilatation of the air-cells. In inflating the lungs, great care is necessary not to force the air so as to tear the pulmonary tissue. If the air pass into the cavity of the pleura, the animal will die immediately, as occurred in the curious experiments of M. Leroy d'Etiole. CHAPTER XVII. COURSE OF THE ARTERIAL BLOOD. This function has for its object to transport the arterial blood from the lungs to every part of the body. Of the Arterial Blood. The arterial blood is essential to the execution of the func- tions. A celebrated physiologist defined life as the contact of the arterial blood with the organs, particularly the brain. We have nothing to add here to what has been already said of the arterial blood in the article Respiration. I will only refer to some im- portant facts relative to the blood generally, which will complete the history of this liquid. The learned Vauquelin found in this fluid a large quantity of fatty matter, of a soft consistence, and which was at first regard- ARTERIAL BLOOD. 411 ed as fat. But M. Chevreul, by a series of very ingenious exper- iments, has discovered that this matter is the same as that of the brain and nerves. Its chemical composition is very remarkable. It is an azotic fat, the reverse of all other bodies of this kind, which do not contain azote. Messrs. Prevost and Dumas have demonstrated the presence of urea in the blood of animals deprived of their kidneys. M. Boudet, Jun., has found cholesterine, and some other elements of the bile, in the serum. Thus, as the analyses of the blood multi- ply, and the processes become more perfect, we find in the blood all the elements of the organs. We may now designate with confidence the fibrine as the same substance as the muscular fibre ; the albumen, which forms so great a number of the mem- branes and tissues; the fatty matter that has been described, which, united with osmazome and albumen, form the nervous system; the phosphates of lime and magnesia, which constitute the greater part of the bones; the urea, one of the most remark- able excrementitial elements of the urine; the yellow matter of the bile, and which extends itself by imbibition into the cellular tissue about contusions, &c. When, by the aid of a strong mag- nifying-glass or microscope, we examine the transparent parts of cold-blooded animals, we discover in the sanguineous vessels an innumerable multitude of small, rounded particles, which swim in the serum, rolling one over the other as they pass from the arter- ies to the veins. These are the globules, or, more properly, the discs of the bloogl; they were discovered by Malpighi. Lee- wenhoek soon after engaged in examining them, probably with- out having given much attention to the vague communication of Malpighi on the subject. He described very precisely a great number of them. Since that time many persons have undertaken their examination; but there are only three that can be compared with Malpighi in the accuracy of their observations and their skill in the use of the microscope; these are Leewenhoek, Hewson, and Messrs. Prevost and Dumas. As they agree in the principal facts, and as the last have made use of the facts indicated by the others, we shall confine ourselves to their results. They found globules in the blood of all animals. To ascertain this, a very small drop of blood may be placed upon a plate of glass, taking care to spread it lightly, without crushing it. Upon the edges there will always be found isolated globules or discs, that may be easily seen and measured. With weak lenses they appear like black points; afterward they assume the appearance of white circles, in the midst of which is seen a black spot, when the magnifying power is in- creased. When magnified to three or four hundred times its di- ameter, the last presents the appearance of a bright spot. When the eye has become familiarized with this appearance, it preserves its powers of perception with weaker magnifiers. This is the key to most of the opinions that have been advanced upon this sub- ject, and serves to reconcile them. 412 NUTRITIVE FUNCTIONS. While the blood circulates in the vessels, the particles which it encloses have no other motion than that impressed upon them by the liquid. But it has been said that when removed from the ves- sels, they are vividly agitated, and that the little drop presents a peculiar tremour, which ceases in a few seconds. Sir Everard Home supposed that the blood contains globules, which are en- closed, in health, in a covering of colouring matter, of which they are the nucleus; and within thirty seconds after the blood has been taken from the vessels, that this exterior matter collects to- gether, and forms a sort of collar about the central globule. Messrs. Prevost and Dumas differ from him essentially on this point, they regarding as the habitual state that which seemed to him as the effect of death. Their proofs appear to be irrefraga- ble, as they repose on observing the circulation in the wing of a bat, the foot of a frog, the mesentery of certain fish, the tail of a tadpole, and the lung of a salamander. They satisfied themselves, by numerous observations, that the appearances and diameter of the globules or discs were the same within and without the vessels. They saw that they were not endowed with a movement of rotation on their centre, as some writers had supposed, but that they followed simply the direction of the blood. It is easy to distinguish, in the foot of the frog and the tail of the tadpole, the different phases of the globules, and to satisfy ourselves of their flatness. Sometimes they are seen full; at others, more or less obliquely; again, their edge is presented to the observer. They balance themselves in the liquid in which they swim, and sometimes we see them turn slowly upon them- selves, so that we can exactly appreciate their form. Still farther, we can see them pass directly from the arteries into the veins, and the blood arrive on the one side and return on the other. There may be seen, at the same time, all the varie- ties of position which render so clear the truo form of the globules of the blood. This disposition of the vessels enables us to con- ceive the alteration that has been sometimes remarked in the course of the blood, and the retrograde motion of the circulation during death, on which Spallanzani and Haller have so much in- sisted. These different observations are sufficient to demonstrate that the globules of the blood are the same during life, and for some mo- ments after they have issued from the blood-vessels, and that they are flattened in both instances. But they leave it still doubtful whether they possess elasticity, and whether they consist, as Hew- son believed, and as Messrs. Prevost and Dumas thought they had proved, in a globule enclosed in a membranous sack. Since the publication of their memoir, the latter gentlemen have examined the lung of a salamander with a magnifier of three hun- dred diameters' magnifying power. The spectacle presented to them cannot easily be comprehended by the reader. The san- guineous particles moved with such velocity that at first caused a sensation of vertigo in the observer. But the circulation soon be- ARTERIAL BliOQD. 413 came slower, and the particles could be seen to pass tranquilly along in the fluid in which they were contained; they crept slow- ly, as it were, in the small vascular ramifications, elongating them- selves when the space was too narrow; or they stopped and re- mained for some time in the narrowest passages, until, pressed upon by those coming after them, they broke through the obsta- cle, and passed on. Sometimes they were suddenly stopped by the compact space which separated two of the vessels. It ap- peared as if a very flexible floating body had struck, at its centre of gravity, an obstacle which suddenly stopped its farther progress, the particle bending itself to the form of the opposing body. Still, as the current of the liquid continued to press on in the same di- rection, it would continue to oscillate for some time, uncertain whether to direct itself upon the vessel at the right or the left. Sometimes this state of things would continue for several min- utes. It would probably have been still longer delayed, if the new particles coming in the same direction had not determined it One way or the other. These different movements left no doubt in their minds as to the form of the particles of the blood being membranous sacks, with a globule enclosed. Though, at the pe- riod of the publication of their memoir on this subject, their proofs of this were not decisive, yet they have not since found any rea- sons to doubt the conclusions at which they then arrived. [On this point, however, it would seem there is still some rea- son to doubt. According to Dr. Carpenter, in man and most of the mammalia these particles or globules of the blood, as they have been usually called, are, in fact, discs with a circular out- line. In man the sides of .the disc are somewhat concave, the bright spot constituting the centre. This, which has been regard- ed as indicating the existence of a nucleus, Dr. Carpenter thinks, in reality, is attributable simply to the greater thinness of the disc at this point. The form of the disc appears to be altered by vari- ous re-agents. In water they assume a globular form. The fol- lowing cuts, after Wagner, will illustrate these views. (Fig. 37.) Discs of the Blood, magnified about 500 diameters. ©©•-* ^ D® C$ A. Single discs, a a. Their flattened globules. B. Globules seen edgeways. C D. Lymph globules. With respect to the existence of a nucleus, Dr. Carpenter thinks it doubtful as regards the mammalia. But in the frog, the parti- cles of which are much larger than in man, a nucleus may be ob- served to project. 414 NUTRITIVE FUNCTIONS. (Fig. 38.) Particles of Frog's Blood. The red globules in the blood of the frog are larger than in man. A A. Their flattened face. B. Globule turned edgeways. D. Appearance when changed by dilute acetic acid. C. Lymph globule. Thus, it appears, by taking fresh blood from an animal, and spreading it in thin laminae, we may arrive at results as to its state during life. This is precisely the method of Messrs. Prevost and Dumas. They have described in their memoir their mode of measuring the diameters of the particles. The process presents some difficulties, undoubtedly; we may hope that a long use of the microscope has enabled them to execute it with some precis- ion. In the works of Haller may be found his attempts to do this, as of others who had preceded him. The following are some of the results : Jurin......3^40 part of an English inch. According to experiments revised and approved by Leewenhoek Young..... Wollaston .... Bawer..... Kater..... The last-mentioned number very nearly agrees with the obser- vations of Messrs. Prevost and Dumas in twenty examinations of sound, and nearly the same number of diseased persons. They could trace no difference connected with age, sex, or disease. It is probable, however, that some difference exists, and the late re- searches of M. Bawer may lead to the discovery. With respect to inequalities in the particles in the same blood, this is very doubtful. Nothing can be more regular than that of the particles in the human blood. It is very rare that particles are observed different from the rest in their diameter. Messrs. Prevost and Dumas always found, where this appeared to be the case, it was a mere optical illusion. It appears, then, that the method adopted by Messrs. Prevost and Dumas presents results comparatively, if not absolutely, ac- curate. They are all that the present necessities of the science claim. They show that the particles of the blood are circular in the mammiferi, and elliptical in birds and cold-blooded animals; ARTERIAL BLOOD. 415 and that they are flat in all animals, and composed, at least in some, of a nucleus enclosed in a membranous sack.] Apparatus of the Arterial Blood. It is composed, first, of the pulmonary veins ; second, of the left cavities of the heart; third, of the arteries. Pulmonary Veins. They arise, like the other veins, in the tissue of the lungs; that is, they consist at first of an infinite number of radicles, which are continuations of the pulmonary artery; these branches, uniting, form small trunks, which gradually become larger. At last all these trunks terminate in four vessels, which, after running a short distance, open into the left auricle of the heart. The pulmonary veins differ from 'all other veins in this, that they do not anasto- mose with each other when they have acquired a certain size. We have observed a similar disposition in the divisions of the ar- tery which is distributed to the lungs. The pulmonary veins have no valves, but their structure in other respects is similar to the other veins ; their middle membrane is, however, a little thick- er, and seems to possess a greater degree of elasticity. Left Cavities of the Heart. The form and size of the left auricle differ but little from the right; its surface only is smoother, and does not present any fleshy column (except in the appendix called oricule). It com- municates by an oval opening with the left ventricle, which is distinguished from the right by the greater degree of thickness of its walls, and the number, volume, and disposition of its fleshy columns. The opening by which the auricle and ventricle com- municate is garnished by what is called the mitral valve, which is very analogous to the tricuspid. The ventricle gives origin to the artery called the aorta, the orifice of which presents three semi-lunar valves very similar to the pulmonary artery. Of the Arteries. The aorta is to the left ventricle what the pulmonary artery is to the right, though it differs in many important particulars. Its capacity and extent are much greater; nearly all its divisions are considered as arteries, and have each received particular names. Its branches anastomose with each other in various modes; they often present numerous and remarkable flexuosities. They are distributed to every part of the body, and effect in each a pecu- liar arrangement; they communicate with the veins and lym- phatic vessels. In other respects the structure of the aorta strong- ly resembles the pulmonary artery; its middle membrane is, how- ever, much thicker, and more elastic. Through pearly its whole extent the aorta is accompanied by filaments, arising from the ganglions of the great sympathetic nerve. These filaments ap- pear to be distributed to its walls. 416 NUTRITIVE FUNCTIONS. Course of the Arterial Blood in the Pulmonary Veins. In treating of the course of the blood in the pulmonary artery, we pointed out how this fluid arrived at the extreme branches of this vessel. The blood does not stop there; it passes into the ex- treme branches of the pulmonary vein, and soon into the trunks of this vein ; in its passage, its motion is gradually accelerated as it passes from the small into the large veins. It does not run with a jerk, and is nearly of equal rapidity in the four pulmonary veins. But let us inquire, What cause determines the progress of the blood in these veins ? We naturally refer this to the contraction of the right ventricle, and the elasticity of the walls of the pulmonary ar- tery. Indeed, having forced the blood to the extreme ramifica- tions of the pulmonary artery, we cannot conceive why these two causes should not continue its motion even in the pulmonary veins. This was the opinion of Harvey, who first demonstrated the true course of the blood; but modern physiologists have found this explanation too simple. It is now generally admitted that, when the blood has arrived at the extreme ramifications of the pulmonary artery, and entered the radicles of the pulmonary veins, or, as they are commonly called, capillary vessels of the lungs, it no longer moves from the influence of the heart, but by an action peculiar to the small vessels that it traverses. This idea of the action of the capillary vessels is extremely convenient in physiol- ogy ; after the vital properties, there is nothing which more facil- itates our explanation of the most obscure phenomena. Let us, therefore, examine it with attention; and first, has this action of the capillaries been witnessed by any observer ? Does it fall with- in the scope of our senses ? No ; no one pretends to have seen it; it is only a thing supposed.* But let us admit for an instant the existence of this capillary action; in what does it consist ? Is it a greater or less degree of contraction, by which the blood, with which they are filled, is forced forward ? In contracting from their elasticity, they would undoubtedly propel the blood ; but can any reason be assigned why they should direct it rather towards the veins than arteries ? Finally, when the small vessels were once emptied, how would they be filled again ? This could only be by the force of the heart propelling blood into them, or else from their dilating in such manner as to attract this fluid from the neighbouring vessels; according to this supposition, it would be as likely to attract the blood from the veins as from the arteries. If we admit, therefore, a position, which is merely gratuitous, that the capillary vessels dilate and contract themselves alternately, we still should not be able to explain the function attributed to them. That they may perform this function, it would be neces- sary that each capillary vessel should be arranged in a manner * This action is directly contrary to observation. In the lungs of reptiles we may see the blood pass from the arteries into the veins with a common magnifying glass, but no action of these vessels. But the slightest.change of dimension is very apparent; it is the same in certain warm-blooded animals, where the blood can be seen traversing the capilla- ries. ARTERIAL BLOOD. 417 analogous to the heart; that it should be composed of two parts, in which one dilated, while the other contracted itself, and that there should be between them a valve analogous to the mitral valve. Yet, even with this complicated apparatus, the course of the blood in these vessels would not be uniform. In whatever point of view, therefore, we examine this action of the capillary vessels, it is found vague and contradictory. In reptiles, in which, by the aid of a microscope, it is easy to distin- guish the blood of the pulmonary artery passing into the veins, no motion can be perceived at the point where the artery terminates in the veins ; the motion of the blood is nevertheless manifest, and even rapid. We must conclude, then, that the capillary action of the vessels of the lungs giving motion to the blood in the pulmo- nary veins is a mere supposition, an effort of the imagination; in a word, purely hypothetical; and that the true cause of the pas- sage of the blood into the pulmonary artery and veins is the con- traction of the right ventricle of the heart. I am far from thinking that the small vessels at all times equal- ly favour the passage of the blood; we have a proof to the con- trary at each inspiration and expiration. When the lungs are distended with air, its passage is easy; but when the chest is con- tracted, the lungs containing but little air, it becomes more diffi- cult. It is, besides, extremely probable that they dilate them- selves, according to the quantity of blood which traverses the lungs, and many other circumstances. I am ready to believe that, according as they are distended or contracted, they may in- fluence the progress of the fluid that traverses them; but I cannot admit that they are capable of modifying the course of the blood, or that they are the sole agents of its motion. The eighth pair of nerves appears to have a great influence upon the passage of the blood through the lungs. It is very prob- able that it modifies the disposition of the capillary vessels of these organs; when we inject water into the pulmonary artery, in the dead body, it passes immediately into the veins; a part of it, how- ever, escapes into the cells of the bronchiae, where it mixes with the air, and forms froth; another portion escapes, and becomes infiltrated into the cellular tissue of the lungs. After a certain time, when this infiltration has become somewhat considerable, it then becomes impossible to force the injection farther into the pul- monary veins. Similar phenomena occur when, instead of water, blood is injected into the pulmonary artery. These phenomena, as we have seen, have a great analogy with those produced by the section of the eighth pair of nerves in living animals. When we recollect the extremely small calibre of the capilla- ries of the lungs, we can comprehend the remarkable tenuity of volume of the globules of the blood, and their utility. If the solid and insoluble part of the blood had not been divided into these very minute masses, it could not have traversed the minute ves- sels by which the arteries are united to the veins. Experiment proves this; I injected into the veins of an animal an impalpable G G G 418 NUTRITIVE FUNCTIONS. powder of charcoal and sulphur, suspended in a little gum-water. The animals died almost immediately; on opening their bodies, I found the pulmonary capillaries completely choked up by the in- jected powder, which was too gross to pass them. If the blood be very viscid, and its particles separate with great difficulty, the circulation will soon stop, because the blood cannot traverse the lung, and it becomes engorged. Many grave mal- adies, no doubt, owe their origin to this cause. We may cause almost immediate death in animals by introducing viscid substan- ces into the circulation, such as oil, mucilage, metallic mercury, &c, as was observed by M. Gosford (Journ. de Physiol., t. L). In diseases attended with alteration of the pulmonary tissue, as pneumonitis, gray hepatization, &c, I have satisfied myself that the passage of an aqueous injection from the pulmonary artery to the veins is extremely difficult, or even impracticable. In certain ca- ses, where there existed before death an abundant expectoration, the injection passed into the bronchiae. In a word, I have strong reasons to suspect that most organic lesions of the lungs consist in an obstruction, to a greater or less extent, of the blood through the pulmonary capillaries; consequently, of an extravasation of the different elements of the blood into the parenchyma of the lungs. Absorption of the Pulmonary Veins. Like the other veins, the pulmonary veins absorb, and carry to the heart, those substances which are in contact with the spongy tissue of the air-cells of the lungs. It is sufficient to inspire once air charged with odoriferous particles, in order that it may be- come manifest in the animal economy. The deleterious gases, medicinal substances spread through the air, contagious miasmata, certain poisons or medicines applied to the tongue, produce effects which astonish us by their promptitude. The mode by which the absorption is effected, which was long unknown, and the object of numerous speculations, is extremely simple. It depends on the physical properties of the vascular walls. If a gas or vapour penetrate into the lung, these substances traverse the membranes which form the walls of the small vessels, and mingle with the blood. If it be a liquid, it is imbibed by the same walls, and en- ters the cavity of the vessels. It soon becomes mingled with the blood, and as the walls are very thin, the passage, or, what is the same thing, the absorption, is very rapid. In epidemic and contagious diseases, it is most desirable to seek for remedies which, in the form of vapour, gas, &c, may be introduced with the air into the lungs. The attendants upon per- sons labouring under dangerous diseases, where the emanations are fetid, should take great precautions, by ventilation and clean- liness, to avoid breathing them. ARTERIAL BLOOD. 419 Passage of the Arterial Blood through the Left Cavities of the Heart. The mechanism by which the blood traverses the left auricle and ventricle is the same as that by which the venous blood trav- erses the right cavities of the heart. When the left auricle dilates, the blood is poured in by the four pulmonary veins, and fills it. When, afterward, it contracts itself, one part of the blood passes into the ventricle, another flows back into the pulmonary veins. When the ventricle dilates, it receives blood from the auricle, and a small portion from the aorta. When it contracts itself, the mi- tral valve is raised, and closes the opening between the auricle and ventricle, so that the blood cannot return into the auricle; it is, therefore, forced into the aorta, pushing before it the three semilunar valves with which the vessel had been closed during the dilatation of the ventricle. It is proper, however, to remark that, as there are no fleshy col- umns existing in the left auricle, it cannot be supposed to have the same influence upon the blood that we have supposed to be exerted by the right; and, as the left ventricle has much thicker walls than the right, it must compress the blood with much great- er force, which is indispensable, from the great distance this fluid has to pass over. Course of the Blood in the Aorta, and its Divisions. Notwithstanding the differences which exist between this and the pulmonary artery, the phenomena of the course of the blood are nearly the same. Thus, a ligature being applied upon this vessel near the heart in a living animal, it becomes contracted through its whole extent, and the blood, with the exception of a certain quantity which remains in the principal arteries, passes in a few moments into the veins. Some authors have called in question the fact of the contraction of the arteries under these circumstances. We may demonstrate this by the following experiment: Lay bare the carotid artery in a living animal for several inches in extent; tie it at two differ- ent points; take with a compass the transverse dimensions of the vessel, and you will then have a portion of the artery full of blood; make into the walls of this portion of the artery a small opening, and you will immediately see the blood almost entirely pass out, darting even to "some distance. Measure, afterward, the size with a compass, and you will not then doubt that the artery is very much contracted, if the prompt expulsion of the blood has not already convinced you. The experiment proves also, con- trary to the opinion of Bichat, that the force with which the ar- teries react upon themselves is sufficient to expel the blood they contain. I will immediately give other proofs of this. During life, this total expulsion cannot take place, because the left ventri- cle throws out, at every moment, new masses of blood into the aorta, and this blood replaces that which is continually passing into the veins. 420 NUTRITIVE FUNCTIONS. Every time that the ventricle forces blood into the aorta, it is distended, as well as all its ramifications of a certain calibre. But this dilatation becomes less as the arteries become smaller, and it ceases altogether in those which are very small. These phenomena are, as we see, the same already described in speak- ing of the pulmonary artery. The explanations that we then gave may with propriety be applied here. The polished surface of the interior of the arteries must be very favourable to the motion of the blood; we know, at least, that it diminishes when this is removed by certain diseases ; the course of the fluid becomes slower, and sometimes ceases altogether. This is probably also the reason why blood will not pass long through a tube introduced into the extremity of an open artery. It is very probable that the friction of the blood against the walls of the arteries, its adhesion to these walls, its viscid nature, &c, must have great influence upon its motion. But it is impossible justly to appreciate these different causes, either combined or sep- arate. Independently of these phenomena common to all the ar- teries, there are some which are peculiar to the aorta, and which depend upon the anastomoses existing between its branches, and the innumerable curvatures which are found in the greater num- ber of them. Whenever an artery presents a curvature, there is, every time the ventricle contracts, a tendency in it to assume a straight line; this tendency manifests itself by an apparent motion, called by some authors locomotion of the artery, and which may be consid- ered as a principal cause of the pulse. This motion is most re- markable when it is observed near the heart, and in one of the large arteries. In the arch of the aorta it is most apparent. It may be easily explained. One consequence to be deduced from this fact is, that it is mechanically impossible that the windings of the artery, particularly when they are sudden, should not retard the course of the blood. Bichat is entirely mistaken in this re- spect, when he asserts, that the meanderings of the artery have no influence. This could not happen, he says, unless the arteries were empty when the heart sent forward its blood to them ; but, as they are constantly filled, this effect cannot take place. Now, inasmuch as each curve of the artery has such a force expended upon it as to give the vessel a tendency to become straight, there will be, necessarily, so much less force for the motion of the fluid ; and, of consequence, its motion will be retarded by these curvatures. It is much more difficult to explain the influence of the different anastomoses. Their utility is very evident; through them the ar- teries mutually supply each other, and distribute blood to the or- gans ; but we are unable to say, with accuracy, what influence they exert upon the progress of the blood. If the dimensions, curves, and anastomoses of the arteries essentially modify the course of the blood, it is impossible that all the organs in which each of these circumstances exist in different degrees should re- ceive the blood with the same degree of rapidity, and, of conse- ARTERIAL BLOOD. 421 quence, with the same force. The brain, for example, receives four large arteries for itself alone; but these arteries run in a very tortuous direction, with many sudden turns, before they penetrate the cranium; when they have arrived there, they anastomose very frequently; and, finally, they do not enter into the tissue of the* organ until they have become extremely small. The blood must therefore circulate but very slowly in this organ. The kid- ney, on the contrary, has but one artery, which is short and volu- minous, which at once buries itself in its parenchyma, and is di- vided into large branches; the blood must, therefore, pass through it with great rapidity. Thus, by all the concurrent circumstances which modify the course of the arterial blood, it becomes resolved into a very com- plicated hydraulic problem, viz., the continued distribution of a fluid, varying essentially in quantity and rapidity in different parts, through a single system of tubes, of unequal capacity, by means of a single agent of alternate impulsion. In the number of phenomena exhibited in the course of the ar- terial blood, we have placed the dilatation and contraction of the arteries. Bichat does not admit the existence of these phenome- na. This author will not allow that the arteries dilate at the in- stant when the ventricle contracts; and he formally denies that they contract to force the blood into the different parts. I think, however, that, with a little attention, it is possible to see distinct- ly these two phenomena when the artery is laid bare. They are, for example, evident in the large arteries, such as the thoracic and abdominal aorta, especially in large animals; but to render them apparent upon smaller arteries, we may make the following experiment: lay bare the crural artery and vein of a dog to a cer- tain extent; then pass behind these two vessels a ligature, which must be drawn very tight over the posterior part of the thigh. The arterial blood will thus be prevented from arriving at the limb, except through the crural artery, and can only return through the crural vein. Measure with a compass the diameter of the ar- tery, afterward press it between the finger and thumb, so as to in- tercept the blood, and you will see, in a short time, that part of the artery which is beyond the fingers become emptied of the blood which it contained. Allow the blood afterward to pene- trate into the artery, by removing the compression; you will then see it again become distended with blood at each contraction of the ventricle, and resume its former dimensions. But though I consider the contraction and dilatation of the ar- teries as a point completely ascertained, I am far from thinking, with some authors of the last century, that they dilate themselves, or that they are contracted by muscular fibres. I think, on the contrary, that they are passive in both cases; that is, that their dilatation and contraction are simply the effects of the elasticity of their walls acted upon by the blood, which is continually for- ced" into their cavity by the contraction of the ventricles of the heart. 422 NUTRITIVE FUNCTIONS. There is a difference in this respect between the large and small arteries; I have proved, by direct experiments, that the ar- teries do not exhibit any evidences of irritability; that is, they re- main immovable under the application of pointed instruments, caustics, and a stream of the galvanic fluid. Not being able to detect the contractility of the walls of the arteries, Bichat thought it necessary to deny the important phenomenon which he suppo- sed to be the effect of it. He did not believe that the blood ran on in a continued stream in these vessels; but he supposed that the entire mass of fluid was displaced at the instant that the ven- tricle contracted, and was immovable when it was in a state of relaxation, as would happen if the walls of the arteries were in- flexible. This opinion has been supported very recently by Dr. Johnson, an English physician. He has even constructed a ma- chine which, according to him, renders this thing evident. But it is sufficient to open the artery in a living animal to see that the blood will pass out in a continued stream; with a jerk if the ar- tery be large, and uniformly if it be small. Now the action of the heart being intermitting, it is impossible that it should pro- duce a continued stream. The arteries must, therefore, act upon the blood. The elasticity of the arterial walls has the effect of a reservoir of air in certain pumps, which act alternately, and which, there- fore, furnish the fluid in a continued stream. We know, in gen- eral, in mechanics, that every intermitting motion may be chan- ged into a continued one by employing the force that produces it to compress the receiver, which reacts in a continued manner. Passage of the Arterial Blood into the Veins. When an injection is forced into an artery in the dead body, it returns promptly by the corresponding vein. The same thing takes place, and with still greater facility, if the injection be made into the artery of a living animal. In cold-blooded animals, by the aid of a microscope, we can distinguish the blood passing from the arteries into the veins ;* the communications between these two kinds of vessels is, then, direct, and extremely easy. It is natural to suppose that when the heart has forced the blood into the extreme arteries, that it continues to give it motion after it has reached the branches, and even the trunks of the veins. Har- vey and a great number of distinguished anatomists have thought the same. Bichat has opposed, with great force, this doctrine, and has endeavoured to fix limits to the influence of the heart. He supposes that this action ceases at the point where the arteries terminate in the veins. According to him, the action of these small vessels alone is the cause of the motion of the blood. We have already combated this supposition, in speaking of the course of the blood in the lungs; the same reasoning applies per- fectly here. Bichat asserts that this capillary action consists in a * Cowper asserts that he witnessed the same phenomenon in warm-blooded animals: I have repeated his experiments without success. ARTERIAL BLOOD. 423 " kind of oscillation or insensible vibration of the walls of these ves- sels." Now I ask how an oscillation or insensible vibration of the walls can determine the motion of a fluid contained in a canal ? Again, if this vibration be insensible, who can undertake to decide upon its existence ? Let us not, therefore, render complicated a simple question, by a supposition vague and destitute of proof; but let us admit an explanation which presents itself naturally to the mind, viz., that the contraction of the heart is the principal cause of the motion of the blood, both in the arteries and veins. The following experiments appear to me to render this phe- nomenon very evident. After having passed a ligature about the thigh of a dog, in the mode just pointed out, that is, without including either the crural artery or vein, apply a ligature separ- ately upon the vein near the groin, and make a slight puncture in the vessel; the blood will then escape, forming a jet. Then press the artery between the finger and thumb so as to prevent the arterial blood from passing to the limb ; the jet of venous blood will not stop instantly, but it will continue for a few moments. At last, however, the column will diminish, and finally stop, though the vein may be full through its whole extent. If, during the pro- duction of these phenomena, we examine the artery, we shall see that it becomes gradually contracted, and at last completely empty. At this period of the experiment, let the compression upon the artery be removed, and the blood, being propelled by the heart, will soon arrive at the extreme ramifications of the ar- tery ; the column of blood will now be soon seen to pass out from the opening in the vein, and by degrees the jet will become per- fectly established as before. Compress anew the artery until it becomes empty ; afterward, allow the blood to penetrate slowly. Under these circumstances, the blood will continue to pass out in a small stream from the vein, but not in a jet, which will, how- ever, take place when the artery is left entirely free. Analogous results may be obtained by forcing an injection of warm water into the artery instead of allowing the blood to penetrate it; the more force used in pushing forward the injection, the more prompt- ly will the fluid pass out from the vein. I observed, in speaking of the lymphatic vessels, that they com- municate with the arteries, and that injections pass readily from one into the other. This communication becomes still more evi- dent when we inject saline or coloured fluids into the veins in a living animal. I have satisfied myself often that these substan- ces pass into the lymphatic vessels in the course of two or three minutes, and that their presence may easily be demonstrated in the lymph extracted from these vessels. As long as the veins which pass out from the organs are free, the blood which arrives by the arteries traverses their parenchy- ma, and is not accumulated. But if the veins are compressed, or are unable to empty themselves of the blood which they contain, this fluid, still continuing to arrive by the arteries, and finding no opportunity to escape into the veins, becomes accumulated in the 424 NUTRITIVE FUNCTIONS. tissue of the organ, distends the sanguineous vessels, and augments more or less its volume, especially if its physical qualities be such as to favour these changes. This phenomenon may be observed in many organs; but, as it is most apparent in the brain, it has been most frequently remarked there. This swelling of the brain from an obstruction in the circulation happens whenever the course of the blood through the lungs is interrupted; and as this takes place generally during expiration, the brain at this moment becomes swollen in proportion as the expiration is longer and more complete. In young animals, where the brain receives pro- portionally more arterial blood, the swelling is much more re- markable. Remarks on the Motions of the Heart. The right auricle and ventricle, and the left auricle and ventri- cle, the actions of which we have investigated separately, really form but one organ, the heart. The auricles contract and dilate at the same moment; the motion of the ventricles is also simulta- neous. When we speak of the contraction of the heart, it is to the ventricles that we particularly refer. Their contraction is called the systole, and their dilatation, the diastole of the heart. The contraction of the auricles is generally abrupt and rapid, and is often twice to one contraction of the ventricles. Their dilatation is slower, because it depends upon the blood of the venae cavae and pulmonary veins ; if these veins be full, it distends them promptly. The sanguineous columns are sometimes poured so rapidly into the auricles, that their walls do not contract, except as far as depends upon their elasticity. I have frequently observ- ed this phenomenon in the inferior animals, and have no doubt that it also often happens in man. Here, as in many other in- stances, elasticity advantageously supplies the place of muscular contractility. Every time that the ventricles contract, the whole of the heart is thrown suddenly forward, and the apex of this organ strikes against the walls of the left side of the chest, near the space be- tween the sixth and seventh true ribs. This is accompanied with a particular sound, of which we shall soon speak. This dis- placement anteriorly of the heart during its systole has given oc- casion to a long and spirited controversy. Some contend that the heart becomes shortened during its contraction; others main- tain that it becomes elongated, and that this is necessarily the case ; otherwise it could not strike against the walls of the tho- rax, inasmuch as it is more than an inch distant from it during its diastole. A great number of animals were uselessly sacrificed in examining this motion of the heart; at the same moment some asserted that they saw the heart shortened, while others as strong- ly affirmed the reverse. What experiments could not determine, a very simple reasoning makes clear. Bossuet interfered in the controversy, and showed that, if the heart were elongated in its systole, the mitral and tricuspid valves, being retained by the ARTERIAL BLOOD. 425 fleshy columns, could not close the openings between the ventri- cles and auricles. The partisans of the lengthening of the heart persisted no farther; but it remained to be shown how the ventri- cle could be shortened as the heart was carried forward. Senac proved that this depended upon three causes. First, the dilata- tion of the auricle, which takes place during the contraction of the ventricle; second, the dilatation of the aorta and pulmonary ar- tery, in consequence of the blood introduced into them by the ventrieles; third, the tendency in the arch of the aorta to be thrown into a straight line by the contraction of the left ventricle. The contraction of the ventricles and the motion of the heart against the left wall of the thorax are accompanied with a dull, but distinct sound, when the ear is applied to the cardiac region. This sound is preceded by another sound, that has been noticed in speaking of the right ventricle, which accompanies the dilatation of that cavity. These two sounds, which succeed each other rap- idly, constitute what are called in pathology the sounds of the heart, and are important in the organic and other affections of this organ. Both result from the shock or impulsion of the heart against the walls of the chest. The first, or the dull sound, depends, as I have said, on the impulsion of the apex of the heart on the interspace between the sixth and seventh rib. It may be produced at other points, if by any cause the heart is displaced, or the parietes of the thorax deformed. The dull character of the sound appears to depend on the mass of the striking body, and the little elasticity of the body struck. The second sound corresponds to the dilatation of the ventri- cles, and the consequent rapid entrance of the blood into its cavi- ties. The production of this sound has been attributed to the con- traction of the auricles ; and also to the blood being suddenly in- troduced within the ventricles, and striking against the walls, so as to excite sonorous vibrations. But neither of these explana- tions is well founded. I have already stated, that when the heart is exposed, at the moment it acts with the greatest energy, no sound is produced unless it strikes against some of the neighbour- ing parts. If we introduce through the thoracic walls of a dog, as I have repeatedly done, a small movable stem over the right ventricle, and another over the apex of the heart, it will be easy to see that each of these sounds is accompanied by a shock, which manifests itself clearly on the outside by an extensive movement of these small stems. If the second sound be clearer, it is no doubt attributable to the inconsiderable mass of the striking body, and to the part struck, the sternum, which is much more sonorous than the lateral wall of the thorax, which is chiefly muscular. The number of pulsations of the heart is considerable, and is greatest in the early periods of life. At birth it is from 130 to 140 in a minute. At one year, 120 130 " At two years, 100 110 " At three years, 90 100 " Hhh 426 NUTRITIVE FUNCTIONS. At seven years it is from 85 to 90 in a minute. At fourteen years, 80 95 At the adult age, 75 80 In old age, 65 75 Extreme old age, 60 65 " But these numbers vary according to an infinite number of cir- cumstances, such as sex, temperament, individual disposition, &c. The affections of the mind have a great influence upon the rapid- ity of the contractions of the heart; every one knows that an emo- tion, however slight, modifies these contractions, and often accel- erates them. Diseases produce great changes in this respect Many researches have been made to ascertain the force with which the ventricles contract. To appreciate that of the left ventricle, an experiment has been made, which consists in crossing the legs, placing the ham of one leg upon the knee of the other, and suspending at the end of the foot a weight of fifty-five pounds. This considerable weight, though placed at the extremity of so long a lever, is raised at every contraction of the ventricle, in con- sequence of the tendency to become straight, which occurs in this accidental curve of the popliteal artery, when the legs are cross- ed in this manner. This experiment shows that the contractile force of the heart is very great, though it does not enable us to form any accurate estimate of it. The mechanical physiologists made great efforts to express it in numbers ; Borelli compared the force with which the circulation is carried on to a power that would be necessary to raise a weight of 180,000 pounds ; Halles supposed it to be 51 pounds 5 ounces; and Keil reduced it to five or eight ounces. Which shall we consider the truth among such palpable contradictions? M. Poiseuille has invented an ingenious instrument with which he proposes to measure the force of the heart, avoiding the obstacles which opposed the means of appreciation employed by his predecessors. This instrument consists of a curved tube, the vertical part of which is graduated with a metrical scale, and filled with mercury; the horizontal part, which is to be adapted to the arteries and veins, is filled with a solution of the sub-car- bonate of soda, which prevents the blood from coagulating. He has called this instrument the hemo-dynamometer. With this instrument M. Poiseuille has arrived at results which, though not such as might have been desired as relates to deter- mining the force of the heart, are at least very remarkable as re- spects the mechanical phenomena of the circulation. I will cite the following fact, that it would have been difficult to foresee in the actual state of science. If the instrument be fitted to a large or a small artery near to or remote from the heart, the height of the mercurial column is the same. Thus, when applied to the carotid of a horse, the point of elevation of the mercury is the same as when applied to a small dog. From the identity of these results, the author con- cludes that a molecule of the blood is moved with the same force ARTERIAL BLOOD. 427 through the whole course of the arterial system; a conclusion which appears to us to go beyond what the experiments prove. To generalize, as this author has done, would require certain experi- mental data, not in those vessels which are large enough to have this instrument adapted to them, but the more minute vessels, even the capillaries, if possible. M. Poiseuille afterward establishes the following general theo- rem : The total static force which moves the blood in an artery is exactly in direct proportion to the area which the circle of that ar- tery presents, or in direct proportion of the square of its diameter, wherever it may be situated. It appears to be impossible to determine precisely the force developed by the heart during its contraction. It is obvious that it must vary with a multitude of causes, such as the age and size of the individual, the quantity of blood, state of the nervous sys- tem, the action of the organs, health and disease, &c. All that has been said respecting the force of the heart applies to its contraction. Its dilatation has been regarded as an active phenomenon, and I have myself entertained that opinion. But it does not appear to me to be so at present. In again carefully studying the dilatation of the heart, it has seemed to me that its contraction compresses the fibres of the organ, that their elas- ticity is developed under this influence, and that immediately, as soon as the contraction ceases, the fibres return to their natural length with the more energy in proportion as they have been compressed. There is developed, as we have seen, a phenome- non of this kind immediately after the contraction of a bundle of muscular fibres, the effect of the galvanic current To this phys- ical cause of the dilatation of the cavities of the heart we must add the force of the column of blood which is introduced into them by the auricles, and which is undoubtedly a powerful influ- ence in separating their walls. It must be kept in mind that the auricles contract with considerable force, pouring the blood into the cavities of the ventricles. The contraction of the right ventricle, then, through the medium of the pulmonary artery and veins, is one of the causes of the dilatation of the left ventricle. The con- traction of the left ventricle acts in the same way in the dilata- tion of the right auricle, through the medium of the blood that fills the arteries and veins; lastly, the contraction of each auricle contributes to enlarge the ventricle to which it is attached. From the first moment of the existence of the embryo until death takes place from decrepitude, the heart continues to beat. What is the cause of this ? This question has often been propo- sed, both by ancient and modern philosophers and physiologists. The causes of phenomena are not easily assigned in physiology. It almost always happens that what are considered such are no- thing more than descriptions of these phenomena in different terms. But it is curious to remark the facility with which we suffer our- selves to be abused in this respect; the different explanations of the motion of the heart are most palpable proofs of this. The 428 NUTRITIVE FUNCTIONS. ancients asserted that there was in the heart a peculiar virtue, a concentrated fire, which gave motion to this organ. Des Cartes imagined that there took place in the ventricles a sudden explo- sion, like that from gunpowder. The motion of the heart was af- terward attributed to the animal spirits, the nervous fluid, the pra- ses systematis nervosi, and the archeus; Haller considered it as an effect of irritability. Recently M. Legallois has endeavoured to prove, by experiments, that the principal cause of the motion of the heart had its seat in the spinal marrow. These experiments of M. Legallois consisted in destroying suc- cessively, in living animals, the spinal marrow, by introducing a metallic staff into the vertebral canal. The result is, that the force with which the left verticle contracts diminishes in pro- portion to the destruction of the spinal marrow, and when it is complete, the heart no longer possesses power of propelling the blood to the extremities. From these experiments, which have been multiplied and varied with great ingenuity, M. Legallois concludes that the cause of the motion of the heart exists in the spinal marrow. As it has been remarked that this organ contin- ues to contract for a considerable time after the complete destruc- tion of the spinal marrow, and that its motions continue regular even after it has been separated from the body, M. Legallois ex- plains these facts by saying that these motions are not the true contractions of the heart; that they are only the simple effects of the irritability of the organ. To make good this explanation of M. Legallois, it would be ne- cessary to show, by experiments, in what the difference between the irritability of muscular fibres and their power of contraction Consists. This important distinction not haying yet been estab- lished, I conceive that we cannot conclude from the labours of M. Legallois anything more than that the spinal marrow has an in- fluence upon the force with which the heart contracts; but we can by no means infer that it is the cause of the motions of the heart. The organs which transmit to the heart the influence of the brain and spinal marrow are nervous filaments coming from the eighth pair, and perhaps a great number of filaments of the cer- vical ganglions of the great sympathetic. M. Dupuytren and myself have endeavoured, for several years, to determine, by the extraction of the cervical ganglions, and even the first of the tho- rax, the influence of the ganglions upon the motion of the heart; but our efforts have been thus far unsatisfactory. The animals have nearly all died in consequence of the wound unavoidable in extracting them. We have never remarked any direct influence upon the heart. Remarks on the Circulation of the Blood. We are now acquainted with all the links that form the chain Which the sanguineous system represents. We know how the blood is carried to the lungs, and to every part of the body, and ARTERIAL BLOOD. 429 how it returns again to the heart. Let us now examine these phenomena in a general manner, that we may impress the most important of them more strongly upon our minds. The quantity of blood contained in the sanguineous system is very considerable,. It has been estimated, by many authors, at from twenty-four to thirty pounds. This estimate cannot be very exact, as the quantity must vary according to a variety of causes. Youth and infancy have a larger proportion of blood than advan- ced age. It is more than probable that full-grown individuals, whose bodies are well developed and life active, have more blood than debilitated and emaciated persons, Plethoric .persons, also, who are subject to hemorrhages from the nose and hemorrhoi- dal veins, must have a larger quantity of blood than those wlio are not thus constituted. Experiments made by me upon dogs have given results analogous to these conjectures as respects man. A dog of middle size does not furnish, by rapidly bleeding to death, but about a pound if emaciated and weak; if vigorous and in good condition, it may furnish double that quantity. We know but little better the difference between the mass of arterial and venous blood. The last, being contained in vessels the car pacity of which is superior to the arteries, must necessarily conT tain the most, though we cannot say exactly how much it exT ceeds. The size of the body bears a certain relation to the quantity of the circulating fluid. Persons of great stature have an enor- mous quantity of blood, as we may see by the copious and re- peated bleedings they are capable of enduring, and from the state of the blood-vessels after death. In some individuals the aorta and its divisions, and the venous system, are two, or even three times more capacious than the same organs in others of the same height, but less corpulent. In living animals the dimensions of several of the organs may be increased at pleasure. Take, for example, the spleen of a dog; after the abdomen has been opened, transfuse a pint of the blood of another dog into its veins. On doing so, you will see the spleen gradually enlarge, until, by the time that the injection is comple- ted, it will become a third, or even a half larger than at first Or, perform the opposite experiment; after measuring the size of the spleen in an animal, bleed it until it faints. On doing so, you will see the spleen diminish sensibly in volume in proportion as the blood is poured out. Similar observations may be made on the liver, but the tissue of that organ being less extensible than that of the spleen, the changes in volume are less remarkable. It is easy to satisfy one's self that the length of the intestinal canal and the thickness of its walls are also in proportion to the circulating mass. In strong, vigorous, and plethoric individuals, in whom the abdomen is much developed, the walls of the intes- tines are very thick, the cavity large, and the length of the canal more than twelve yards. In thin persons, whose abdomen,is flat instead of prominent, and who have little blood, the parietes of 430 NUTRITIVE FUNCTIONS. the tube are thin, the cavity narrow, and the whole length often does not exceed five yards. We may easily make analogous ob- servations upon the skin. What has been said of the dimensions of the spleen, as relates to the volume of blood, may throw some light upon the functions of this singular organ. From what we have said, the spleen is a true reservoir, with elastic walls, which press constantly on the contained blood, and which tends to make it pass into the system of the vena portae. The thinness and want of elasticity in the walls of that vein, and the absence of valves, readily allow the blood pressed by the spleen to penetrate there. The spleen also may more readily expel the blood contained in it, not only from its elasticity, but from its possessing a peculiar contractile power, which is quite apparent under the influence of certain drugs, par- ticularly the nux vomica. The circle through which the blood passes being uninterrupt- ed, and the capacity of the canal being very variable, the rapid- ity of this fluid must be very different; because the same quantity must pass through every part in a given time, which is confirmed by observation. The rapidity is greatest in the trunk and princi- pal branches of the aorta and pulmonary artery; it diminishes much in the secondary branches, and still more at the point where the arteries terminate in the veins. It afterward aug- ments, as the blood passes from the extreme vessels into the larger trunks of the veins, but its rapidity is never as great in the venae cavae as in the aorta. In the trunks and principal divisions of the arteries, the motion of the blood is continued, not only by the influence of the elastic power of the arteries, but it is also thrown out in a jerk by the contraction of the ventricles ; this jerk manifests itself in the arter- ies by a simple dilatation in those which are straight, and by a dilatation and an effort to become straightened in those which are flexuous. The first phenomenon with which this second cir- cumstance is connected is the pulse. It is not easy to study this in man or animals, except at those places where the arteries run upon the bones, because there they do not move from the finger applied over them, as is the case with those which float in the midst of soft parts. The pulse frequently makes us acquainted with the principal modifications of the contraction of the left ventricle, its prompti- tude, intensity, weakness, and regularity or irregularity. We know also by the pulse the quantity of the blood; if it be great, the artery is rounded, large, and resisting; if little, the artery is small, and easily compressed. Certain states of the arteries in- fluence the pulse, and may render it different in the principal ar- teries. The pulsations of the arteries are necessarily perceptible in the neighbouring organs, in proportion as the arteries are large, and the organs yield easily. The agitation they experience is consid- ered favourable to their action, though there is no positive proof ARTERIAL BLOOD. 431 of this. In this respect no organ is influenced more than the brain. The four cerebral arteries, uniting in circles at the base of the cranium, elevate the brain at each contraction of the ven- tricle, as may be easily seen by laying bare the brain of an ani- mal, or by observing this organ in wounds of the head. It is probably to moderate this agitation that the numerous curves of the internal carotid and vertebral arteries are jfia.de, before their entrance into the cranium. These flexuosities must necessarily retard the course of the blood through these vessels. When the arteries penetrate into the parenchyma of organs in large trunks, as the liver, kidney, &c, the organ must undergo great agitation at each contraction of the heart. The organs where the vessels do not penetrate until they have become divided and subdivided, do not experience this. All the blood that passes from the lungs to the left auricle of the heart is of the same nature; it, however, sometimes happens that it is not precisely similar in the four pulmonary veins.* I£ for example, a portion of the lungs be altered to such an extent that the air cannot penetrate into its air-cells, the blood that traverses it will not be changed from venous to arterial blood; but it will arrive at the heart without having undergone this transformation. In its passage, however, through the left cavi- ties, it will be intimately mixed with the rest of the blood. The blood which goes from the left ventricle must necessarily be homogeneous, until it reaches the farthest branches of the aorta; but when it arrives at the smallest vessels, its elements become separated. There exist a great number of parts, such as the serous membranes, the cellular tissue, the tendons, the aponeu- roses, the fibrous membranes, &c, in which we cannot distinguish the red blood, and where the capillary vessels contain only se- rum. This division of the elements of the blood is only found in a state of health. When the parts just mentioned become dis- eased, it often occurs that their small vessels are filled with red blood. It has been attempted to explain this analysis of the blood in the small vessels. Boerhaave, who .admitted the existence of several kinds of globules of different sizes in the blood, asserts that globules of a certain size can only pass into vessels of a given calibre. We have already seen that the globules as de- scribed by Boerhaave do not exist. Bichat believed that there existed in the small vessels a peculiar sensibility, in consequence of which they would receive only that part of the blood adapted to them. We have already frequently combated ideas of this kind; they are not admissible here, because the most irritating fluids, when introduced into the arteries, pass immediately into the veins, without their passage being opposed by the capillary vessels. One of the most singular ideas that has ever entered the ima- * See the experiments of Legallois. 432 NUTRITIVE FUNCTIONS. ginations of physiologists is, that living bodies are not subject to physical laws; that life is in constant opposition to these laws: as if such opposition were possible ; as if one phenomenon could be op- posed to another. It is on this principle, which is repugnant to common sense, that the influence of weight, and the different posi- tions of the body upon the circulation, has been but little studied. However, there can be no doubt of the existence of such; influ- ence, and that it is very great. Both medical and surgical em- piricism is forced to recognise it. In many cases it is quite evi- dent that the blood moves with more difficulty when propelled against its own weight; while, on the other hand, it passes more easily to those parts where it is carried by its own weight. During sleep, and in the horizontal position, the blood is more freely directed towards the head. Dr. Bourdon remarked in himself that, when lying upon one side, the blood accumulated in the more dependant part of the head, swelling the pituitary mem- brane on that side, and intercepting the passage of air in the cor- responding nostril. When he turned to the opposite side, the ob- structed nostril became free, while that on the opposite offered the same phenomenon. Thus the powers which circulate the blood have often to over- come the weight of the fluid, while universal gravitation exer- cises a remarkable influence over the circulation. This fact mer- its the attention of physicians; for, however slightly the functions are deranged, the effects of physical laws become manifest In traversing the small vessels, the blood is deprived of its ele- ments ; sometimes the serum escapes, and spreads itself over the surface of the membrane ; at others, the fat is deposited in its cells; here it is the mucus, there the fibrine; and, besides, there may be foreign substances that have become accidentally mixed with the arterial blood. By losing these different elements, this fluid ap- proaches the character of venous blood. At the same time that the arterial blood supplies those parts which are lost, the small veins absorb the substances in contact with them. For example, in the intestinal canal they take up the drinks; on the other hand, the lymphatic trunks pour the lymph and chyle into the venous system. It is certain, therefore, that the venous blood cannot be homogeneous, and that its composition must vary in the different veins. But having arrived at the heart by the motions of the right auricle and ventricle, and the disposition of the fleshy col- umns, all its elements become intimately mixed before it passes into the pulmonary artery. There is a general law of the economy, that no organ can con- tinue to act unless it receives arterial blood; the result, therefore, is, that all the functions are dependant upon the circulation. But, in its turn, the circulation is dependant upon respiration, which forms the arterial blood ; nor can it exist without the action of the nervous system, which has a great influence upon the rapidity and course of the blood, and its distribution to the organs. In fact, under the influence of the nervous system, the motions of the heart ARTERIAL BLOOD. 433 increase or diminish, and, of consequence, the general course of the blood is increased or retarded. Again, when the organs act voluntarily or involuntarily, observation shows that they receive an increased quantity of blood without the general circulation being at all accelerated ; if their action be very considerable, the arteries leading to them have their action increased; if, on the contrary, their action diminishes, the arteries are retracted, and only allow a small portion of blood to arrive at the organ. These phenomena are manifest in the muscles; the circulation becomes more rapid when they contract; if they often contract, these ar- teries increase in volume; if they are paralyzed, the arteries be- come very small, and the pulse scarcely perceptible. The nervous system, then, influences the circulation in three different ways. First, in modifying the motions of the heart. Sec- ond, in modifying the capillaries of the organs so as to accelerate or retard the course of the blood. Third, in producing the same effects in the lungs, that is, in rendering more or less easy the course of the blood through these organs. The acceleration of the motions of the heart becomes perceptible to us from the pul- sation of its apex against the walls of the chest; an obstruction in the capillary circulation is known by a sensation of numbness, and a particular sort of pricking. When the pulmonary circulation is difficult, we are aware of it from a sense of oppression or suffoca- tion. It is probable that the distribution of the filaments of the great sympathetic nerve to the walls of the arteries answers some important purpose, but we are completely ignorant of their use; experiment has thrown no light upon this point. The composition of the blood must exercise great influence upon the mode of action of the organs ; but we have still very imper- fect notions of the chemical variations that this liquid undergoes. According to some works upon the blood, this fluid is always the same. It is probable that the progress of animal analysis will soon lead us from these imprecise ideas; some facts, at least, seem to indicate this. If we introduce into the jugular vein of a dog a few drops of water which has remained a little time in contact with animal substances in a state of putrefaction, in the course of an hour after the introduction the animal will be depressed, and lie down. Soon he will be attacked with an ardent fever; will vomit black and fetid matter; his alvine evacuations will be similar; the blood will have lost its power of coagulation, will be extrav- asated into the tissues, and death will soon follow. These phenomena, which are very analogous to certain diseases of the human subject, as the black vomit in yellow fever, &c, ap- pear to originate in an alteration in the composition of the blood. I think, even, that I have discovered that the dimensions of the globules diminish in proportion as these symptoms become devel- oped. This is in harmony with the passage of the blood through the walls of the small vessels, and the hemorrhages which are its effect. There is one mode of alteration that may be easily appreciated, 111 434 NUTRITIVE FUNCTIONS. I mean the respective proportions of the serum and coagulum. I wished to see what would be the effect upon an animal to gradu- ally diminish the solid and insoluble portion of the blood. For this purpose, I took a healthy dog and bled it eight ounces. The blood, when examined the next day, had but little serum; about one eighth part. I replaced the blood drawn, by injecting about half a pound of water into the jugular vein. The next day I re- peated the bleeding and injection ; the blood was now one fourth part serum, and three quarters coagulum. Two days afterward I repeated the same processes, and continued in this way every two days until the tenth day. Then there was three fourths serum and one fourth coagulum; the animal had become weak, moved with difficulty, appeared to have lost his instincts and caressing habits, his cerebral faculties were diminished and stupified; indeed, he was no longer the same animal. No doubt, then, a certain composition of the blood is one of the conditions important to the exercise of the different functions. These remarks induced me to try the injection of warm water into the veins in the human subject. The individual on whom I made this experiment was labouring under hydrophobia, and at the point of death. The introduction of a pint of water calmed his fury as if by enchantment.—(See Journal de Physiol., t. hi.) Of the Influence of the Inspiratory and Expiratory Muscles upon the Motion of the Blood. We have demonstrated that the heart is the principal agent of the circulation. For the most part, its contractile force deter- mines the progression of the blood ; but there are other auxiliary powers which often intervene with great energy, and which ex- ercise a great influence over the course of the blood, so as to sus- pend it completely. These powers are those which draw in and expel the air from the chest. During the dilatation of the thorax, the blood of the venae cavae superior and inferior, and proportionally that of the other veins, is attracted towards the heart. The mechanism of this attraction is similar to that of the air in the lungs ; it is, if we may be allowed the expression, an inspiration of venous blood. On the contrary, during expiration, all the pectoral organs being compressed, the venous blood is repelled; it flows back in the veins towards the organs, and the arterial blood arrives at its destination with the more promptitude, because to the pressure of the left ventricle is added that of the expiratory muscles. These different phenomena are not striking in a quiet state, but when the respiration is forced, in the great muscular efforts which often accompany it, they are very remarkable. The knowledge of these facts is derived from the labours of Haller, Lamure, and Larry; it supplies the means of explaining many phenomena which have much embarrassed physiologists. I now propose to enter into some details, in consequence of the great importance of the subject. ARTERIAL BLOOD. 435 If we observe for some time the external jugular vein of one whose neck is very thin; or, what is still better, lay bare this vein in a dog, it will be very obvious that the blood moves through its cavity under very different influences. In general, when the chest dilates to inspire, the vein will be seen to be suddenly emptied; its walls will be flattened, and in contact The vein on the other hand, swells, and is filled with blood when the chest contracts. These effects are more striking as the respiratory movements are more marked. Those of expiration are most remarkable when the animal struggles. The respiratory actions are not the only causes of the motion of the blood in the jugular veins. With a little attention, we may perceive that the contractions of the right auricle sensibly influ- ence it; they produce a sort of irregular palpitation in the vessels. When the auricle contracts, the blood is repelled towards the head; on the contrary, it is attracted towards the heart by its dil- atation. When there is an accidental coincidence of the dilata- tion of the chest and the auricle, or of the contraction of these parts, the movement of the blood in the jugular is regular; i. e.f the vessel is emptied and filled suddenly. But as the motions of the auricle are much more frequent than those of the thorax, it necessarily happens that this coincidence frequently does not ex- ist ; hence the beatings of the jugular are very irregular. This phenomenon is especially observed in very severe diseases, and was called by Haller the venous pulse. The explanation of these phenomena, as given by Haller and Lorry, is very simple and satisfactory. When the chest is dilated, it inspires, or sucks up the blood from the venae cavae and the other veins. The mechanism of this inspiration or motion is nearly the same as that by which the air is drawn into the trachea. When the chest contracts, on the contrary, the blood is crowded back into the venae cavae in consequence of the pressure that all the pectoral organs, the heart, blood-vessels, and lungs, necessarily undergo during expiration. Hence the alternate fulness and emp- tiness of the jugulars. To prove that this phenomenon is exactly in relation with a similar phenomenon which takes place in the venae cavae, I intro- duced a gum-elastic sound into the jugular vein until it reached the vena cava, or even the right auricle of the heart. I found that the blood escaped from the extremity of the sound only at the period of expiration. On the contrary, during inspiration the air was suddenly drawn into the heart, and gave rise to certain accidents that will be hereafter mentioned. The same results were obtained by passing the sound through the crural vein to- wards the abdomen. There can be no reasonable doubt, then, of the modifications that respiration exerts upon the blood in the principal venous trunks. We may also easily discover that expiration sensibly acceler- ates the movement of the arterial blood, by opening an artery in 436 NUTRITIVE FUNCTIONS. one of the extremities. This is especially observable when the animal struggles and makes strong expiratory efforts. As we cannot always induce the animal to make these expiratory efforts at our will, we may have recourse to the process recommended by Lamure, i. e., compress the sides of the thorax with the hands. On doing so, we shall see the arterial jet of blood enlarge or di- minish in proportion to the pressure exerted. Inasmuch as respiration was observed to produce this effect on the course of the blood in the arteries, it seemed probable that it might influence the progress of the venous blood, not only through the medium of the veins, as we have already seen, but also through the arteries. I thought this conjecture worth testing by experi- ment. I placed a ligature upon one of the jugular veins of a dog; the vessel was emptied below the ligature, and swelled very much above it. I then pricked slightly with a lancet the distended por- tion, so as to make a very small opening. I thus obtained a jet of blood that the ordinary movement of respiration did not sensibly modify, but which tripled or quadrupled in size when the animal made a vigorous effort. It may be objected that the effect of the respiration was not transmitted by the arteries to the open vein, but by the veins which remained free, and which would have transported the blood repelled from the venae cavae towards the vein that was tied, by means of the anastomoses. It was easy to remove this difficulty. The dog has not, like man, large internal jugulars, which re- ceive the blood from the interior of the cranium. In this animal, the internal jugular is little more than a vestigium, the blood from the head and neck passing almost entirely by the external jugu- lars, which are very large. By tying at the same time both these veins, I was sure of preventing the reflux referred to, to a great extent. But so far from this double ligature preventing the phenomenon spoken of, the jet, on the contrary, was still more strikingly in accordance with the movements of the respiration; it was even obviously modified in ordinary respiration, which, as we have seen, did not take place with a single ligature. To ren- der this still more evident, I might observe, the action of the cru- ral vein, which, with its branches, is garnished with valves which may be said to oppose the reflux ; if there was an increase of the jet during expiration, it is manifest that the impulsion must cer- tainly come from the side of the arteries. This result I uniformly found in many experiments. The cru- ral vein being tied and pricked below the ligature, the jet was ob- served to increase sensibly in full expirations, and during the me- chanical compression of the walls of the thorax with the hands. With the instrument of M. Poiseuille I recognised and obtained a sort of admeasurement of these phenomena. These, as well as the preceding experiments, necessarily lead to a striking change in the explanation of the swelling of the veins ARTERIAL BLOOD. 437 during expiration. According to Haller, Lamure, and Lorry, this swelling is the consequence simply of the crowding back the blood of the venae cavae into the branches which open into them, mediately or immediately. But it is now manifest that to this must be added the arrival into the veins of a larger quantity of blood coming from the arteries. The same modification must apply to the motions of the brain in connexion with resjAation. It is not necessary, then, to at- tribute the swelling of that organ, at the moment of expiration, to the mere reflux of the blood in the veins; nor its sinking, at the moment of inspiration, singly to the sucking up of the fluid to- wards the chest. But the influence of respiration upon the prog- ress of the arterial blood, and of it upon the blood in the veins, through the medium of the arteries, must constitute an important element in that explanation. It appears to me that we may comprehend the phenomenon in this way. At the moment of a strong expiration or effort, all the thoracic and abdominal organs are compressed ; the arterial blood is driven forward, more particularly in the ascending branches of the aorta. The abdominal aorta is also compressed, and admits the blood with difficulty in proportion to the pressure it undergoes, as has been well described by Lorry. The blood thus arrives more abundantly at the head, and tends to pass more promptly to- wards the veins which return it to the heart, which would im- mediately take place if the veins were free. But so far from this, the pressure exerted upon the thoracic organs has caused a reflux of the venous blood in the vessels which contain it, though this retrograde movement does not extend very far, in consequence of the valves which oppose it. But the blood which flows back in the veins soon meets with the blood which arrives from the arteries; the vessel becomes distended, and the course of the fluid in the veins is suspended. This is the simple explanation of the swelling of the brain. We must also refer to these movements of flux and reflux of the blood, the entrance of the cephalo-rachidian fluid into the cav- ities of the brain through the opening of the fourth ventricle, and its passing out from these cavities. At the moment when the si- nuses and rachidian veins are distended, the compressed liquid passes into the aqueduct, traverses the third ventricle, and. soon reaches the lateral ventricles. Afterward it passes in an oppo- site direction, by the same route, at the instant of respiration or the sucking up of the venous blood. But what takes place in the brain must also occur in the other organs, with modifications, as relates to the disposition of their san- guineous vessels. The whole of the medulla spinalis becomes enlarged, the spleen elongated, the face reddened and swollen during crying, prolonged running, muscular efforts, and violent passions. The veins of the extremities swell under the same cir- cumstances, and if you induce a person while bleeding to breathe strongly, the jet of blood sensibly augments. An individual suf- 438 NUTRITIVE FUNCTIONS. fering with a phlegmon of one of the limbs experiences more vivid pain in the diseased part, on lifting a weight, running or crying, &c. All these phenomena, and many others analogous to them, depend evidently on the accumulation of blood in the organs du- ring expiration, which urges forward the arterial, and opposes the return of the venous blood. It results from these facts, that one of the consequences of great expirations and violent efforts is the mo% or less prolonged sus- pension of the circulation, which is more or less complete as the expiration or effort is more violent. Hence, probably, the im- possibility of continuing great efforts beyond a few seconds, and the necessity of profound inspirations immediately afterward. Many circulatory phenomena appear to be connected with this momentary stagnation of the blood in the tissues; as apoplexies, nasal and other hemorrhages, sometimes the consequence of violent efforts ; copious perspiration of tumblers after their exertions ; the sudden headaches which follow defecation in some individuals; priapism observed in persons executed by hanging, &c. It is not necessary that the glottis should be completely closed in order that the effects of expiration become manifest, as some have supposed ; for considerable efforts often take place concur- rently with cries forming grave sounds, which permit an easy issue to the expired air. We have demonstrative proof of this in the practice of veterinary surgeons, who often introduce a large metallic canula between the thyroid and cricoid cartilages of hor- ses, in order to render their respiration easier. Though the pas- sage to the lungs is thus kept constantly free, these animals are still enabled to continue their laborious employments. Another proof may be drawn from experiments in which we compress the sides of the thorax with the hands, and thus accelerate the course of the arterial or venous blood. In this case there is no indica- tion of the glottis being closed when the thorax is compressed. I am farther assured of this by the following experiment: I made an opening into the trachea of a dog more than an inch in length, and from four to five lines in width. I then tied one of the jugu- lar veins, and made a small opening above the ligature, through which there passed a continued jet of venous blood. This jet was considerably increased whenever the animal struggled or the thorax was compressed. In terminating this article, I may remark, that the different phenomena above described are more apparent in proportion to the quantity of blood. If studied in an animal that has naturally but little blood, or which has lost a considerable quantity, they will be recognised with difficulty, and their reality appear doubt- ful, as has actually happened to some highly-respectable observ- ers. But if we inject a suitable quantity of water into the circu- latory system, all these phenomena become sufficiently palpable. This fact, which I have repeatedly demonstrated in my courses of lectures, is important to be remembered as respects the phe- nomena that have been thus described. It furnishes another ARTERIAL BLOOD. 439 proof of the great caution necessary to be observed in noting all the physical circumstances that may influence the results when we undertake to investigate an animal function. Of the Transfusion of Blood, and the Infusion of Medicinal Agents. Such is the opposition that men of genius have always met from their contemporaries, that it was thirty years before the dis- covery of Harvey was acknowledged, though the proofs were then most evident But as soon as the circulation was admitted, a sort of delirium seems to have seized upon the profession; it was supposed that the means of curing all diseases, and render- ing man immortal, were discovered. The causes of all our dis- eases were attributed to the blood. To cure them, therefore, no- thing more was supposed to be required than to remove the bad blood, and to replace it with that which was pure, taken from a healthy animal. The first attempts were made upon animals, and were very successful. A dog having lost a large quantity of blood, received by transfusion that of a sheep, and was perfectly restored; an- other dog, old and deaf, recovered by these means the use of his hearing, and seemed to renew his youth. A horse twenty-six years old, having received into his veins the blood of four lambs, acquired new vigour. The experiment of transfusion was now tried upon man. Denys and Emerez, the one a physician, and the other a surgeon, of Paris, were the first who made the attempt They introduced into the veins of an insane young man the blood of a calf, in a larger quantity than had been taken from him; he recovered his reason. A case of leprosy, and a quartan fever, were cured by these means; and many cases of transfusion were tried upon men in health without any injurious results. But some sad accidents soon calmed the general enthusiasm excited by these few successful cases. The young man, soon af- ter the experiment, became frantic; he was the second time sub- jected to transfusion, and soon died with a discharge of blood, and in a state of stupor. A prince of the blood royal having also fallen a victim to this practice, it was forbidden by the Par- liament of Paris. A short time afterward, G. Riva, having per- formed the operation of transfusion upon two individuals who died in Italy, the pope forbade it. From that period transfusion has been considered as not only useless, but dangerous ; but as it seems to have succeeded in some cases, it would be an interest- ing inquiry for a person skilled in such experiments to pursue the subject farther. I have had occasion to make a certain number of these experiments, but have never known any instance where the introduction of the blood of one animal into the veins of an- other was attended by any serious inconvenience, even when the quantity of blood thus introduced was much greater than be- fore. But in order that the transfusion may be made without incon- 440 NUTRITIVE FUNCTIONS. venience, it is necessary that the blood should be passed immedi- ately from the animal that gives to that which receives it. If the blood be first received into a vessel or syringe, and afterward in- jected, it will be more or less coagulated, and often becomes the cause of death by choking up the pulmonary vessels. All the ex- periments where this circumstance is not taken in the account have little value. I have seen the transfusion fail and cause death because the blood had to traverse a small tube two inches long, where it partly coagulated before passing into the new circula- tion. A short time after the discovery of the circulation, it was at- tempted to introduce medicines directly into the veins. Some advantages resulted from it in some instances, and inconveniences in others, and it soon fell into discredit; but it has been tried with success in some experiments upon animals. It is an excellent way of judging promptly of the mode of action of a medicine or poison. This process is employed in administering medicine to large animals, in the Veterinary School of Copenhagen; great benefit is found from the promptitude of its action, and great economy in the quantity of medicine employed. An American physician has given to the world a striking ex- ample of his devotion to the progress of knowledge. He injected into his veins a certain quantity of castor oil; fortunately, there was some difficulty in the operation, or he would have been infal- libly the victim of his love of science. We have already shown that viscid liquids, like oil, cannot traverse the pulmonary capilla- ries, but arrest the circulation, and cause immediate death. He estimated the quantity of oil introduced at about two drachms. During the first few minutes Dr. Hales experienced no remakable sensation. " The first extraordinary sensation that I observed," says he, " was an oily taste. A little after twelve, while washing the blood from my hands, and while conversing in very good spirits, I ex- perienced a little nausea, with eructations and rumbling of the bowels ; soon after a singular sensation, but which it is impossible for me to describe, appeared to me to mount suddenly to my head. At the same time I perceived a slight rigidity in the mus- cles of the face and jaw, which cut short my speech, accompani- ed with a sense of alarm and slight faintness. I sat down, and in a short time I felt better. By a quarter past twelve o'clock, I had a good deal of the oily taste, and some dryness of the mouth. I exposed myself freely to the air, and felt better; after having reposed for some time, my pulse was at seventy-five beats in the minute. At thirty-five minutes past twelve, the disorder of the bowels continued, and increased. I felt slight griping pains, as if I had taken a purgative; great nausea and vertigo; my arm felt stiff, but this I attributed to the bandage. At three quarters past twelve, the uneasiness of the bowels had much increased ; the nausea was very great, and there was still the taste of oil; the mouth less dry; in five minutes after, urgent but ineffectual ARTERIAL BLOOD. 441 desire for defecation, and slight pains in the head. At five min- utes past one the pain of the bowels had augmented, and was much aggravated on pressure; the prompting to defecation ur- gent, without the power, the pain continued. At the end of two hours he felt better, and in the course of the day the more urgent symptoms gradually subsided. But he remained ill for three weeks, and did not recover for a long time his usual strength." The injection of medicine into the veins is the only efficacious resource in certain extreme cases where the ordinary use of med- icine is hopeless. ^ On the Introduction of Air into the Veins. It is not easy to conceive by what inadvertence Bichat has re- peated, in twenty places in his works, that a bubble of air acci- dentally introduced into the veins causes sudden death. This assertion is inaccurate. Any may satisfy themselves of this by foroing air into the veins with a syringe. This was announced by me as early as the year 1809, in a memoir read by me before the first class of the Institute. Since that time Nysten has pub- lished a memoir on this subject He not only injected atmo- spheric air into the veins, but most of the known gases. He pro- ved that most of the gases which are soluble in the blood, as ox- ygen and carbonic acid, may be thrown into the blood-vessels in considerable quantity, without serious inconvenience. On the contrary, that those gases which are insoluble often cause acci- dents and death. In my lectures, I have frequently pointed out the difference in the results which arise according to the mode of introduction of air into the veins. If introduced slowly, no injurious effect is pro- duced ; if suddenly, the animal does not fail to experience a re- markable acceleration of the respiration. A peculiar sound is heard in the chest, the evident effects of the change the air under- goes in the venae cavae, the right auricle and ventricle, and the pulmonary artery, &c.; the animal shrieks and dies. The open- ing of the body shows the heart, especially the right side, the pul- monary artery, &c, very much distended with air or a light san- guineous froth, consisting chiefly of air. The same will be found in the cellular tissue of the lungs, where it produces emphysema of the organ, and in the arteries in all parts of the body, particu- larly the brain. Some animals may receive enormous quantities of air into the veins without causing death. On one occasion I introduced with a syringe, with my whole strength and as rapidly as I could, from twenty to twenty-four pints into the veins of an old horse, with- out causing immediate death, though he ultimately sank. On opening him, we found the whole circulating system filled with air mingled with blood, and, what seemed quite remarkable, the lymphatic system distended with an enormous quantity of lymph, slightly yellow, and mingled with a little air. I have often since repeated this experiment, which seems to throw some light on the K K K 442 NUTRITIVE FUNCTIONS. lymphatic system, the uses of which are still but little understood. It would seem from this that it serves as a sort of reservoir, under certain circumstances, for the circulating system when too full. But in artificial plethora, that I have often produced by injecting water, I have never observed the distention of the lymphatic system. These fatal effects of the sudden introduction of air into the veins has been often observed in man during surgical operations, especially where veins in or near the neck have been opened. At the moment of inspiration the external air is drawn into the vein in considerable quantity, and followed by sudden death. The opening of the body shows appearances like those above descri- bed. A similar accident not unfrequently happens in bleeding horses from the jugular vein; generally at the moment when the Vein is in the act of being closed with a pin. CHAPTER XVIII. OF SECRETION, NUTRITION, AND THE GENERATION OF ANIMAL HEAT. In traversing the innumerable small vessels by which the arter- ies and veins communicate, one part of the elements of the blood spreads itself over all the external and internal surfaces of the body; another is deposited in the small hollow organs situated in the substance of the skin and mucous membranes; a third is dis- tributed to the parenchyma of those organs called glands, under- goes a particular elaboration, and is afterward poured out, under certain circumstances, on the surface of the mucous membranes or skin. We give the generic name of secretion to that phenomenon by which a part of the blood escapes from the organs of circulation, and is afterward poured out, either externally or internally, whether it preserves its chemical properties, or whether its ele- ments have undergone a new order of combinations. We gener- ally distinguish the secretions into three kinds: the exhalations, follicular, and glandular secretions. But this division, as it re- spects secreting organs and secreted fluids, is very imperfect. Many organs which secrete cannot be referred either to follicles or glands; what are generally called follicles or glands are organs which differ so much from each other in their form, structure, and the fluids they secrete, that it would perhaps be best not to con- found them under the same denomination. Nevertheless, to avoid anything like an unnecessary spirit of innovation, we shall hereaf- ter speak of the secretions according to this classification. We shall not dwell on this article; for were we to allow it the ex- tension of which it is susceptible, we should greatly exceed the bounds to which we have limited ourselves in this work. OF SENSATION. 443 Of the Exhalations. The exhalations take place either within or without the body, upon the skin or mucous membranes. Hence their distinction into external and internal. Internal Exhalations. Wherever large or small surfaces are in contact, an exhalation takes place ; whenever fluids are accumulated in a cavity with- out an apparent opening, they are deposited by exhalation; the phenomenon of exhalation also manifests itself in almost every part of the animal economy. It exists in the serous, synovial, and mucous membranes, the cellular tissue, the interior of the vessels, and the adipose cells, the internal parts of the eyes and ears, and the parenchyma of many organs, such as the thymus and thyroid gland, and the capsulae renales, &c. It is by exhalation that the aqueous and vitreous humours, and the fluid contained in the lab- yrinth, are renewed. The fluids exhaled in these different parts have not all been analyzed; among those that have, many are found to resemble, more or less, the elements of the blood, and particularly the serum; such are the fluids of the serous mem- branes, of the cellular tissue, and chambers of the eye. Others differ more, e. g., the synovia, fat, &c. Serous Exhalation. All the organs of the head, chest, and abdomen are covered with a serous membrane, which is also extended over the walls of these cavities, so that the organs are not in contact with the walls, or neighbouring viscera, except through the medium of this membrane. As this membrane is very highly polished, the organs can move easily upon each other and upon the walls. The prin- cipal cause that preserves the fine polish is the exhalation. There passes continually from every point of this membrane a very thin fluid, which spreads itself over the neighbouring parts, forming a humid coat, which favours the motion of the organs upon each other. It appears that this power of gliding upon each other is very favourable to the action of the organs. Whenever they are de- prived of this by disease of the serous membrane, their functions are disturbed, and sometimes cease altogether. In a state of health, the fluid secreted by the serous membranes nearly resem- bles the serum of the blood, with a certain quantity of albumen. Serous Exhalation of the Cellular Tissue. The cellular tissue is spread over almost every part of the ani- mal economy. It serves sometimes to separate, and at others to unite different organs, and parts of the same organ. This every- where consists of very small, delicate plates, crossing each other in a thousand different directions, so as to form cells. The size and arrangement of these plates vary in different parts of the 444 NUTRITIVE FUNCTIONS. body. In some they are broad, thick, and form large cells; in others they are very small, thin, and form extremely small cells. In some places this tissue is very extensible; in others it is rigid, offering considerable resistance. But whatever may be the dis- position of the cellular tissue, it exhales from its surfaces a fluid very analogous to that of the serous membranes, and which ap- pears to serve the same purposes. Its use is to facilitate the mo- tion of these membranes upon each other, and, of consequence, to favour the reciprocal motions of the organs and the changes of relation in their different parts. Adipose Exhalation of the Cellular Tissue. Besides the serosity, we find in the cellular tissue, in many parts, a fluid of a very different nature; this is fat. As respects the presence of fat, the cellular tissue may be divided into three kinds, viz., that which contains it constantly, that which contains it oc- casionally, and that in which it is never found. The orbit, the sole of the foot, the ball of the fingers and toes, are always found to exhibit fat. The subcutaneous cellular tissue, and that found on the surface of the heart, loins, &c, present it often; but that of the eyelids and scrotum, and interior of the cranium, never contain it. The fat is contained in distinct cells, which do not communi- cate with the neighbouring ones. This has led to the belief that the tissue containing the fat differed from that containing the se- rum ; but as no one has yet demonstrated these fatty cells, unless when filled with fat, this anatomical distinction appears to me to be very doubtful. The size, form, and disposition of these cells do not differ more than the total quantity of fat that they contain; in some individuals there are but a few ounces, while in others there are many pounds. From the experiments of M. Chevreul it appears that the human fat is almost always yellow ; it is in- odorous, and congeals at variable degrees of temperature. It is composed of two parts, the one fluid and the other concrete; which are again composed qf two new immediate principles, but in different proportions, discovered by M. Chevreul, who calls them " elaine" and " stearine." It is principally by its physical qualities that the fat appears to be useful in the animal economy. In the orbit it forms a sort of elastic cushion, upon which the eye moves with facility; on the sole of the foot and the nates it forms a cushion, which prevents the skin from being injured by the pressure of the body in standing or sitting. Its presence beneath the skin assists in giving rotun- dity to the form, diminishing the projection of the bones and mus- cles, and embellishing the body. As all fatty substances are bad conductors of caloric, it is useful in this respect, fat persons sel- dom suffering from cold in winter. Age and mode of life have a great influence on the production of this substance; young infants are generally fat. It is seldom that it is much developed in youth; but after the age of thirty, especially if the food be nutritious and OF SECRETION. 445 the mode of living sedentary, its quantity augments very much. The abdomen at this period becomes prominent, and the nates and mammae in females become large. The yellow colour of this substance increases in old age. Synovial Exhalation. About the movable articulations we find a very delicate mem- brane, having great analogy to the serous membranes, but differ- ing from them in having small reddish prolongations, containing numerous sanguineous vessels; they have been called franges synoviales. They are very visible in the large articulations of the extremities. It has been long believed by anatomists, and there are some who still think, that the capsules of the joints are folded over the movable cartilages, and cover the surfaces to which they correspond. I have lately satisfied myself that these mem- branes do not extend beyond the circumferences of the cartila- ges. We have spoken of the uses of the synovia in treating of motions. Exhalation of the Interior of the Eye. The different humours of the eye are also formed by exhalation. They are each enveloped by a membrane, which appears to be destined to exhale and absorb them. The humours of the eye are, the aqueous humour, at present supposed to be formed by the ciliary processes ; the vitreous humour, secreted by the membra- na hyaloidea; the crystalline; the black matter of the choroid coat, and that on the posterior surface of the iris. The chemical composition of the aqueous, crystalline, and vit- reous humours has been explained in the article Vision. The black matter of the iris and choroid coat has been analyzed by M. Berzelius. It is insoluble in water and acids; the caustic alkali dissolves it, and the acids precipitate it from this solution. It burns like vegetable matter, leaving a ferruginous cinder. Expe- rience informs us that the aqueous and vitreous humours are rap- idly renewed; when pus or blood have been extravasated into the eye, in a few days they disappear, and the humours resume by degrees their transparency. It does not appear that the cho- roid matter can be reproduced. According to Messrs. Leroy d'Etiole and Coiteau, it would ap- pear that the crystalline may be reproduced. Exhalation of the Cephalo-Rachidian Fluid. Among the most important and abundant, but least known of the exhalations, is the fluid which fills the sub-arachnoidean cavity, which extends to*all parts of the encephalon, fills the inequalities of all parts of its surface, and which extends, with variable de- grees of thickness, from the upper part of the cerebrum to the apex of the sacrum. We have already stated that this fluid passes into the ventricles of the cerebrum and cerebellum, traversing the opening situated at the lower extremity of the fourth ventricle, at 446 NUTRITIVE FUNCTIONS. the part called by the ancient anatomists the point of the calamus scriptorius. The quantity of the cephalo-spinal fluid varies according to many circumstances; this is mechanically necessary in the inverse proportion of the volume of the brain. When the latter is in a state of atrophy, this fluid occupies a considerable part of the cranio-spinal cavity. If one lobe be defective, as sometimes oc- curs in those in whom one arm or leg is contracted and paralyzed, this liquid fills the space which should have contained the deficient portion of the encephalon. I witnessed a case of this in a girl about fifteen years of age, in whom the cerebellum and pons varolii were completely wanting. Having extracted the cephalo-spinal fluid from a horse that had been killed, I placed it in the hands of M. Lapaigne for analysis; the following was the result: Composition of 100 parts. Water . . . . . . . 98.180 Osmazome......1.104 Albumen.......0.033 Chloruret of sodium.....0.610 Subcarbonate of soda .... 0.060 Phosphate and traces of carbonate of lime . 0.009 The soluble phosphorates and phosphates were unsuccessfully sought for in this liquid. The principal agent of secretion of this liquid is the vascular network which clothes the brain and spinal marrow, viz., the pia mater. Sanguineous Exhalations. In all the exhalations that we have now considered, only a part of the principles of the blood pass out from the vessels. The blood itself appears to be poured out into several of the organs, and to fill up the cellular tissue that forms their parenchyma; such are the cavernous bodies of the vagina and clitoris, the ure- thra and glans penis, the spleen and the mammary processes, &c. The anatomical examination of these different tissues seems to show that they are habitually filled with venous blood, the quan- tity of which differs in different circumstances, particularly ac- cording to the state of action or inaction of the organs. There exist many other exhalations of internal, parts, among which I would mention the cavities of the internal ear, of the parenchyma of the thymus and thyroid gland, and of the capsulae renales, &c. But we are scarcely acquainted with the fluids formed in these different parts; they have never been analyzed, and their uses are unknown. * Physiologists have often endeavoured to explain the phenome- non of exhalation. Indeed, each one has given his own opinion on this subject. Some admit the existence of exhaling mouths, others of lateral pores. Bichat has created particular vessels, which he calls exhalants. I say he has created them, for he ac- OF SECRETION. 447 knowledges that these vessels cannot be seen; as the existence of these pores, mouths, and exhalants are not sufficient to explain the diversity in the exhalations, they have been supposed to pos- sess a peculiar sensibility and particular motions, in virtue of which they suffer certain parts of the blood to pass, and refuse a passage to the others. We have little to remark on such expla- nations. It is very certain, however, that the physical disposition of the small vessels has an influence upon exhalation, as the following facts will show. When we inject, in the dead body, warm water into an artery passing to a serous membrane, as soon as the stream is established in the artery and vein, there will be seen upon the membrane a multitude of small drops, which evaporate promptly. Has not this phenomenon great analogy with exhalation ? If we employ a solution of gelatin, coloured with vermilion, to inject a whole body, it frequently happens that the gelatin is deposited about the circumvolutions and inequalities of the cerebrum without the colouring matter having escaped from the vessels; the injec- tion spreads itself, on the contrary, over the external and internal surface of the choroid coat. If we employ linseed oil, coloured with vermilion, we often find the colouring matter separated from the oil, and deposited in the synovial capsules of the large joints, while there is no transudation on the surface of the brain or the interior of the eye. Is not this one of the true post mortem secretions which evi- dently depend on the physical arrangement of the small vessels ? Is it not very probable that the same arrangement presides over exhalation, at least partly, during life ? The theory of exhalation has necessarily changed its aspect since the imbibition of the tissues has been recognised as an es- tablished doctrine. Before seeking in this phenomenon the special influence of life, or, in the received language, the effect of the vital properties, we must begin with the examination of the physical influences. Now we know, by experiment, that the sanguineous and other vessels may be traversed from within outward, or from without in- ward. M. Fodera has made many experiments which leave no doubt on this point. A poisonous substance was introduced with- in an artery which was tied above and below. In a short time the poison was imbibed by the walls of the vessel, spread out- ward, and the animal was suddenly killed. If it had been possi- ble to repeat this experiment on the small vessels, there can be scarcely a doubt that the result would have been still more rapid. The primary physical cause of exhalation is probably the same, then, as that of absorption. Another cause is the pressure the blood undergoes in the circulatory system. This pressure must powerfully contribute to the passage of the more fluid or aqueous part of the liquid through the walls of the vessels. This phenom- enon is easily seen after death, or even during life. If we push forcibly with a syringe an injection of water into an artery, the 448 NUTRITIVE FUNCTIONS. whole surface of the part to which the vessel is distributed, in- cluding its trunk and branches, allows the injected liquid to ooze out, more or less freely, according to the force with which the in- jection is pushed. Another mode of exhibiting this curious phenomenon is to in- ject into the veins of an animal a sufficient quantity of water to double, or even triple the usual volume of its blood. You will thus produce considerable distention of its circulating organs, and of course, by so much, augment the pressure upon the circulating liquid. Examine, then, a serous membrane, the peritoneum, e. g., and you will see the serosity rapidly ooze out from its surface and accumulate in the cavity, producing under your eyes a true drop- sy. I have even seen the colouring matter of the blood escape from the surface of some of the organs, as the liver, spleen, &c. This happens when the veins are compressed, as in oedema and serous extravasations, and no doubt from a similar physical cause. In a word, every cause that increases the pressure upon the blood increases the exhalation. I have often observed this increased exhalation in the vertebral canal, on the pia mater of the medulla spinalis, under the following circumstances. I have also remarked that the sub-arachnoidean cavity, in the living animal, is always filled by the cephalo-rachidean fluid. I have observed that, at certain moments when animals make violent struggles, this seros- ity sensibly increases. It may be seen oozing from the vascular ramifications which constitute the proper envelope of the medulla spinalis. The same thing may also be seen on the surface of the brain, where there exists constantly a thin coat or layer of this liquid. External Exhalations. They consist only of the exhalations of the mucous membranes, and of the skin, or cutaneous transpiration. Exhalations of the Mucous Membranes. There are two mucous membranes : the one covers the surface of the eye, the lachrymal passages, the nasal cavities, the middle ear, the mouth, the whole of the intestinal canal, the excretory ducts, which terminate in it, and, lastly, the larynx, the trachea, and the bronchiae ; the other mucous membrane covers the surface of the organs of generation and the urinary apparatus. These two membranes are constantly lubricated by a fluid they secrete, called mucus. This fluid is transparent, viscid, and of a saltish taste; it reddens litmus paper, contains much water, muriate of potash, and soda, lactate of lime, soda, and phosphate of lime. According to Fourcroy and Vauquelin, the mucus is the same in all the mucous membranes. M. Berzelius thinks, on the contrary, that it varies much according to the parts from which it is taken. Many persons suppose that the mucus is formed exclusively by the follicles of the mucous membranes. I am satisfied, however, by recent experiments, that it is formed in the parts where the follicles OF SECRETION. 449 do not exist; I have also remarked, that it continues to be Jbrmed for some time after death. This merits the particular attention of chemists. [The secretions which cover the mucous membranes appear to be derived from different structures. The glands of the mucous membrane of the intestinal canal have been distinguished by Muller into three kinds, viz., the glands of Lieberkuehn,Brunner,and Peyer. 1st. The follicles of Lieberkuehn are foramina or depressions so small as not to be visible without the aid of a glass, which are spread over the whole extent of the mucous membrane of the small intestines, and are so numerous that, when sufficiently mag- nified, they give to the membrane the dotted appearance of a sieve. The accompanying figure represents the appearance of these fol- licles. (Fig. 39.) Follicles of Lieberkuehn. 1. Are the openings on the surface. 2. The follicles them- selves seen in a perpendicular section. 3. The surface of the cel- lular membrane, with pits for the closed extremities of the follicles. These structures, like those of Brunner and Peyer, are changed in typhoid fever. The annexed figure represents a magnified por- tion of the mucous membrane in fever, after Bcehm. (Fig. 40.) Mucous Membrane in Fever, with the Follicles of Lieberkuehn filled with tenacious white Se- The second kind are the glands of Brunner. These follicles are visible to the naked eye, are distributed singly, and are most numerous in the upper part of the small intestines, especially the duodenum. They are sometimes called the glandulee disgregatee. These glands are deposited in the submucous tissue; their size in health is scarcely that of a hemp seed, and their structure is con- glomerate and very complex. The following figure represents one of these conglomerate mu- cous glands from the duodenum, magnified one hundred times, after Bcehm. L L L 450 IUTRITIVE FUNCTIONS. (Fig. 41.) Gland of Brunner. The third kind of mucous glands found in the alimentary canal are the glands of Peyer, or the glandules agminates. They are chiefly found at the lower portion of the ilium. They are here collected into clusters, or patches, assuming an elliptical form, called from this circumstance by the French les plaques ellip- tiques. Below is a magnified representation of one of these ellip- tical patches, after Boehm. In this view we see also the follicles of Lieberkuehn, the small black dots, and the villi which cover the mucous coat. These structures have become particularly interesting from the changes which are found to take place in them with great uni- formity in typhoid fevers and some other diseases. (Fig. 42.) These oval patches are found on the side of the tube opposite to the mesentery. Their precise nature and uses are unknown, though it is probable that, with the other innumerable 'glandular structures with which the surface of this membrane is covered, one of their functions is to supply mucus to the canal. They are particularly liable to both acute and chronic diseases; care is therefore required to select those subjects for their examination in which this part is perfectly healthy. It appears, from the investi- gations of Boehm and Muller, that in this state, if carefully washed and observed with a good magnifying-glass, they present an ap- pearance thicker than other portions of the canal, owing to the size and number of the villi, which are broader here than in other parts, particularly at their root. The mucous membrane between the villi presents here, as in other parts of the intestines, the nu- merous follicles of Lieberkuehn; but, in addition to these, there are circular white spots, about one line in diameter, in which the mu- OF SECRETION. Ql cous membrane is free from villi; on very few there are traces of very short villi. ' In the human subject these spots are slightly raised. Each of these white spots, of which there are several in a patch of the glands of Peyer, is surrounded by a zone of open- ings like the follicles of Lieberkuehn, presenting in the plate an appearance of small dots. No secretion can be expressed from these white bodies. On rupturing them, a cavity corresponding to their size is found, containing a white, grayish mucus. The appearance of cells or follicles about this part is a morbid appear- ance, and only occurs, according to Muller, after the delicate membrane which covers this cavity has been destroyed, as is fre- quently observed in disease. In most cases of acute and chronic diarrhoea, but especially in typhoid fevers, these structures are found diseased. Modern observations have gone far to show that in the latter the glands of Peyer are diseased from the commence- ment of the fever, and only restored with the restoration of the general health. . A fourth variety of the mucous glands of the intestines are sometimes described under the name of solitary glands. By some physiologists they have been considered as identical with the glands of Brunner. According to Boehm, they are single sacculi, similar to those which, when aggregated, form the patches of Peyer. They are surrounded with a zone of openings, contain a white matter, and become diseased in the same class of cases as the glands of Peyer. They chiefly differ from them in being beset with villi. The accompanying figure is a magnified view of one of these solitary glands, with its openings and villi, after Boehm. (Fig. 43.) When the mucous membrane of the small intestines is inflamed, as in typhoid fevers, the villi become prominent and the follicles of Lieberkuehn become evident, in consequence of their being fill- ed with an opaque, whitish secretion.*] The mucus forms a covering of various degrees of thickness on the surface of the mucous membranes, and is frequently re- newed. Its water evaporates under the name of mucous exhala- tion. It protects the membrane from the action of the air, ali- ments, and various glandular fluids; it seems, indeed, to perform the same office for these m*nbranes as the epidermis for the skin; independently of its general uses, its functions are modified ac- cording to the particular parts of these membranes. Thus, the nasal mucus assists the sense of smell; that of the mouth facili- *Ed. w NUTRITIVE FUNCTIONS. tates taste; that of -the stomach and intestines concurs in diges- tion ; and that of the genital and urinary' passages assists in the functions of generation and urinary excretion. A great part of the mucus is absorbed by the membranes which secrete it; the rest is either thrown off alone, as when we spit, or is mixed with pulmonary transpiration, fecal matter, urine, &c. Cutaneous Transpiratiop.. There is a transparent fluid, with an odour more or less strong, and of a salt and acid taste, constantly passing through the innu- merable openings with which the epidermis is pierced. Most frequently this fluid evaporates as soon as it is brought in contact with the air; but sometimes it runs over the surface of the skin. In the first instance it is imperceptible to the sight; it is then call- ed insensible transpiration; in the second, it is called sweat. Whatever may be the form assumed by this fluid when it escapes from the skin, it is composed, according to M. Thenard, of a large proportion of water, a small quantity of acetic acid, muriate of soda and potash, a little phosphate of lime, an oxide of iron, and a trace of animal matter. M. Berzelius conceives, the acid of the sweat not to be the acetic acid, but the lactic acid of Scheele. The skin also exhales an oily substance, and the carbonic acid. [The sudoriferous glands are seated just beneath the cutis. The excretory ducts open by minute pores in the epidermis, which are seen in elevated lines on the skin of the palm of the hand and the sole of the foot; they penetrate the epidermis rather obliquely, so that a sort of valve is formed, which is lifted up by the excreted fluid. The ducts pass through the epidermis and cutis in a spiral direction, and then enter the glands, which con- sist of the convolutions of the ducts more or less subdivided, on which blood-vessels are distributed; when the epidermis is thin, the canal is straighten The secretion by these glands appears to be continually going on.—(Carpenter.) (Fig. 44.) Opposite is a representation of two of the Sudoriferous Glands. sudoriferous glands from the palm of the hand magnified 40 diameters, after Gurlt. A A. The epidermis.. B B. The tactile pa- pillae. C C. The chorion. D D. The adipose tissue. E E. The two sudoriferous glands. The contorted tubes, or excretory ducts, are seen passing through the skin, and perfora- ting the cuticle.] A great number of experiments have been made to determine the quantity of transpi- ration formed in a given time, and the range of its variation* under different circumstan- ces. The first attempts of this kind were made by Sanctorius, who for thirty years, with extreme care and unwearied patience, weighed his aliments, drinks, solid and fluid OF SECRETION. 453 excretions, and afterward himself. But, notwithstanding his zeal and perseverance, Sanctorius never arrived at any very precise re- sults. Since his time, the subject has been examined with more success; the most remarkable efforts on this subject were made by Lavoisier and Seguin. These gentlemen were the first who distinguished between the loss from pulmonary and cutaneous transpiration. Seguin enclosed himself in an oiled cloth bag that covered the head, with an opening for the mouth, the edges of which were made to adhere about the mouth by a mixture of pitch and turpentine. In this way the pulmonary transpiration alone escaped into the atmosphere. To ascertain the quantity, it was only necessary to weigh himself with the sack, at the begin- ning and end of the experiment, with a very delicate balance. By weighing himself out of the sack, he determined the total quan- tity of the transpired humour; so that, saying nothing of the fluid which he knew had passed out from the lungs, he was in posses- sion of the quantity of humour exhaled by the skin. He kept, besides, an accurate account of his food, solid and fluid excretions, and, in general, of all those causes that might influence transpi- ration. The following are the results of the inquiries of Lavoisier and Seguin: . . . 1. The largest quantity of insensible transpiration, including that of the lungs, is thirty-two grains per minute. 2. The least loss was eleven grains in a minute. 3. During digestion, the loss of weight occasioned by insensi- ble transpiration was at its minimum. 4. Immediately after dinner the transpiration was at its maxi- mum. 5. The medium quantity of insensible transpiration was eigh- teen grains in a minute ; of these, eleven depended upon cutane- ous, and seven on pulmonary transpiration. 6. Cutaneous transpiration only varied during and after eating. 7. Whatever might be the quantity of food taken by any one, or whatever the variations of the atmosphere, the same individ- ual, after having increased in weight to the amount of the whole quantity of food taken, returned every day, at the end of twenty- four hours, to nearly the same weight that he was before ; provi- ded that he was not at the time growing, nor had committed any excess. It is to be regretted that this important undertaking was not continued, and that these authors limited themselves to the'irive|| tigation of insensible transpiration, without extending their obser^ vations to the sweat Whenever cutaneous transpiration is not reduced to vapour, as soon as it is brought in contact with the air,,it appears on the surface of the skin in the form of a liquid; now this effect may occur either from the abundance of the tran- spiration, or from the dissolving power of the air being dimin- ished. We sweat readily in a warm and moist atmosphere by the influence of these two causes, but we sweat much less easily 454 NUTRITIVE FUNCTIONS. in a warm and dry air. Certain parts of the body transpire more abundantly, and sweat more easily, than others; such as the hands, feet, armpits, groins, forehead, &c. In general, the skin of these parts receives proportionally a much greater quantity of blood; and some of them, the armpit, sole of the foot, &c, are excluded from the air. The sweat does not appear the same in every part; every one knows that its odour varies in different parts of the body: the same is true of its acidity ; this appears to be much greater in the armpits and soles of the feet than in other parts. We have seen what influence the volume of the blood, its composition and compression in the vessels, exercise over the in- ternal exhalations. The same circumstances act in an analogous manner on the cutaneous transpiration. Plethoric persons per- spire freely; after the use of warm drinks, which are rapidly ab- sorbed, the exhalation and transpiration equally increase. Last- ly, continued exertion, as walking fast, running, &c, are followed by sweat, especially if the weather be warm. I am acquainted with a person who, when in bed, can sweat at will by contract- ing forcibly, for a short time, his muscular system. Cutaneous transpiration has various uses in the animal econ- omy ; it preserves the softness of the skin, and is favourable to the sense of touch. By its evaporation, together with pulmonary transpiration, it is the principal means of cooling the body, and preserving it at a certain temperature. It would appear that its expulsion from the economy is very important, as, whenever it is diminished or suspended, derangement of the health follows ; and many diseases do not yield until copious perspiration is produced. Follicular Secretions. We give the name of follicles to the small, hollow organs lodged in the skin and mucous membranes, and which have, for this reason, been distinguished into mucous and cutaneous; the follicles are also divided into simple and compound. Mucous Follicular Secretions. The simple mucous follicles are found, over nearly the whole extent of the mucous membranes, more or less abundant; there are, however, parts of these membranes, of considerable extent, where they cannot be detected. Those bodies called the fun- gous papillae of the tongue, the amygdalae, the glands of the car- dia, prostate, &c, are considered by anatomists as collections of s#iple follicles. Perhaps this opinion is not well founded; we know little of the fluid they secrete; it appears to be analogous to the mucus, and to answer the same purposes. Cutaneous Follicular Secretions. In almost every part of the skin there exist small openings, the orifices of small, hollow organs, with membranous walls, ha- bitually filled with albuminous and fatty matter, the consistence, OF SECRETION. 455 colour, odour, and even taste of which vary in different parts of the body, and are continually poured upon the surface of the skin. These small organs are called the follicles of the skin; there is at least one at the base of each hair ;vthe hairs, indeed, often trav- erse the cavity of a follicle in passing out. The follicles form that shining, fatty substance that we see upon the scalp and car- tilage of the ear. The follicles secrete the wax in the meatus auditorus externus, and likewise the thick, whitish matter that we force out from the skin of the face by pressing it^under the form of small worms. This substance, from its external surface being in contact with the air, becomes blackened, and produces the numerous spots that we see in the face of sorne persons, partic- ularly about the nostrils and cheeks. It appears, also, that these follicles secrete the white, odorous matter that is continually renewed about the parts of generation. From being spread upon the surface of the skin, hair, &c, this substance preserves the softness and elasticity of these parts, ren- ders their surface smooth and polished, and favours their motion upon each other. In consequence of its unctuous nature, it in some measure defends them from humidity. Glandular Secretions. We give the name of gland to a secretory organ, which pours the fluid formed by it over the surface of a mucous membrane or the skin by one or more excretory ducts. The number of glands is very considerable ; their action has received the name of glan- dular secretion. There are seven secretions of this kind; the tears, the saliva, the bile, the pancreatic juice, the urine, the semen, and the milk. We may, perhaps, add to these the secretions of the mucous glands and the glands of Cowper. Secretion of Tears. The gland that forms the tears is very small; it is situated in the upper and outer part of the orbit, and a little on the outside of the eye ; it is composed of small granulated masses, united by cellular tissue. Its excretory ducts, small and numerous, pass out at the posterior part of the upper eyelid ; it receives a small ar- tery, a branch of the ophthalmic, and a nerve derived from the fifth pair. In health, the tears are not very abundant; the fluid is lim- pid, inodorous, and of a saltish taste. They were analyzed by Fourcroy and Vauquelin, who found them composed of a great proportion of water, some hundredths of mucus, and muriate, and phosphate of soda, a very little soda, and pure lime. What is generally called the tears is not entirely, however, the fluid se- creted by the lachrymal gland; it is a mixture of this with the matter secreted by the conjunctiva, and probably that of the glands of Meibomius. The tears form a covering to the conjunctiva of the. eye, and defend it from the contact of the air; they facilitate the motion of the eyelids upon the eye, favour the expulsion of foreign bodies, t 456 NUTRITIVE FUNCTIONS. and prevent the action of irritating substances upon the conjunc- tiva ; under these circumstances, their quantity becomes suddenly very much increased. They also assist in expressing the pas- sions ; disappointment, grief, joy, and pleasure cause the tears to be poured out in abundance ; their secretion, it is manifest, is strongly influenced by the nervous system. This influence takes place, probably, through the medium of the nerve sent to the lachrymal gland from the fifth pair of cerebral nerves.* Secretion of the Saliva. The salivary glands are, first, the two parotids, situated before the ear, and behind the neck and ascending process of the inferior maxillary bone ; second, the sub-maxillary gland, situated be- neath and on the surface of this bone; third, the sub-lingual, placed immediately below the tongue. The parotids and sub- maxillary glands have each only one excretory duct; the sub-lin- guals have several. All these glands consist of granulated mass- es, of different forms and sizes. They receive arteries of consid- erable size, in proportion to their volume, and are amply supplied with nerves derived from the brain and spinal marrow. The sa- liva secreted by these glands is continually running into the mouth, and occupies its lower part. It is placed between the anterior and lateral parts of the tongue and the lower jaw at first, and when this space is filled, it is lodged between the inferior lip, the cheek, and the external side of the lower jaw. When deposited in the mouth, it becomes mixed with the fluids secreted by the mucous membrane and follicles. No one has ever analyzed the fluid of the salivary glands sep- arately, but only the fluid found in the mouth, which is, no doubt, almost entirely composed of saliva. It is limpid, viscid, without colour or smell, of a bland taste, and somewhat heavier than wa- ter. Berzelius asserts that it is composed of 992.9 of water, 2.9 of a particular animal matter, 1.4 of mucus, 0.7 of muriate of pot- ash and soda, 0.9 of tartrate of soda and animal matter, and 0.2 of soda. It is probable that the composition of the saliva varies, as it is sometimes sensibly acid. We owe to M. Mitscherlich, a learned physician and skilful chemist, a curious analysis of the saliva taken from an accidental opening in the parotid gland. The same author has also made many interesting remarks on the secretion of the saliva itself. The following are some of them. The quantity of saliva is by so much the less as there is a large quantity of ahments introduced within the mouth. The motion of the jaws increases the afflux of the fluid. During quiet sleep, the parotid secretes so little that it is impossible to collect any. Du- ring speech, M. Mitscherlich collected from his patient, in the course of a few minutes, several drops of very limpid saliva. In twenty-four hours the fistula furnished from sixty-five to ninety- * See, for the other uses of the tears, article Vision. OF SECRETION. 457 five drachms of saliva, varying according to the nature of the ali- ments. The saliva was most frequently found slightly acid; sometime's it was strongly alkaline ; at others, neutral. During the intervals between eating, it was acid; while eating, it became alkaline. The acidity was often observed to disappear with the first mouthful of aliment. The saliva contained hydrochloric, sulphuric, and phos-t phoric acids, but not sufficient to neutralize the alkali. The saliva is one of the fluids most useful in digestion; it fa- vours the mastication and division of the aliments; it assists in deglutition and the formation of chyme, and facilitates the motion of the tongue in speech and singing. The greater part of this fluid is carried into the stomach by the action of deglutition; a small part passes out with the expired air, and evaporates. [The structure of the salivary glands and pancreas in man bears considerabe resemblance to that of the mammae. The fol- lowing figure represents a lobule of the parotid gland of a new- born infant injected with mercury. It is magnified fifty diam- eters.] (Fig. 45.) Lobule of Parotid Gland. Secretion of the Pancreatic Juice. The pancreas is situated in the abdomen, behind the stomach ; its excretory duct opens into the duodenum near to that of the liver. From the granulated structure of this organ, it has been considered a salivary gland; but it differs from them in the small size of the arteries it receives, and from its not having any cere- bral nerve. De Graff, the celebrated Dutch anatomist, discovered a mode of collecting the pancreatic juice ; it consisted in introducing into the intestinal extremity of the excretory duct the barrel of a small quill, which terminated in a little bottle, placed in the abdomen of the animal. I have often attempted to repeat this process, but have always failed. The quill, and every other tube, wounded the mucous membrane of the duct, and the blood, oozing out, grad- ually closed up the mouth of the tube. I had, therefore, recourse to a much more simple method ; having laid bare the orifice of the duct in a dog, I wiped carefully, with a piece of fine linen, the sur- Mmm 458 NUTRITIVE FUNCTIONS. rounding mucous membrane, and then waited until a drop of the juice passed out. As soon as it appeared, I sucked it up by means of a peculiar sort of pipe (pipette), an instrument used in chemis- try. In this way I have been able to collect several drops of this fluid at a time, but never a sufficient quantity to make a regular analysis. I have found it of a light yellow colour, of a saltish taste, and without odour; it possessed alkaline properties, and was partly coagulated by heat.* The circumstance which has appeared the most remarkable to me in endeavouring to procure this fluid, is the small quantity which seems to be secreted. It frequently happens that a drop will not pass out once in a half hour; and I have sometimes waited for a much longer period be- fore it has appeared. Its secretion does not seem to be increased during digestion, but, on the contrary, rather retarded. In gen- eral, I think it is most abundant in very young animals. Messrs. Levret, Lassaigne, and Watrin have made some curi- ous chemical researches on the secretion of the pancreatic juice in the horse. Having placed a horse on his left side, they made an incision into the abdominal walls, and laid bare the duodenum. Having divided the intestine longitudinally, and penetrated into its cavity, they perceived two openings, through which there escaped two sorts of liquids. The one was of a yellowish green; the other less abundant, and colourless; the first, no doubt, was the bile; the other, the pancreatic fluid. They then introduced a sound of gum elastic into the duct of the pancreas, and secured it by a liga- ture. At the other end of the sound there was a gum elastic bot- tle, strongly compressed by a ligature, so as to expel all the air. When the sound was well secured in the pancreatic duct, the lig- ature about the bottle was removed, when, in consequence of its elasticity, the bottle expanded, thus causing a sort of sucking of the pancreatic juice favourable to the experiment. On detaching the bottle at the end of half an hour, it was found to contain about three ounces of a limpid, saltish, and alkaline fluid. Its specific gravity was 1.0026. This fluid, on being analyzed, con- tained, Water......99.1 Animal matter soluble in alcohol ^ The same in water Traces of albumen . . 1 ~ q Mucus,' free soda . . . \ ' ' Chloruret of sodium and potassium J Phosphate of lime . . J Total.....100.0 The same authors have tried the process of Graff and Schuyl upon dogs, but were not more fortunate than myself. They sat- * In birds, which have two organs of this kind, I have remarked that the excretory ducts are endowed with a constant peristaltic motion. The pancreatic juice is also much more abundant; it is almost entirely albuminous; at least, it hardens like albumen, by heat. OF SECRETION. 459 isfied themselves that applying excitants, particularly weak acids, on the duodenal orifice of the pancreatic duct, produced promptly an abundant excretion of the pancreatic juice. Messrs. Tiede- mann and Gmelin procured the pancreatic juice of a dog and a sheep by a process very analogous to that of De Graaf The most important result at which they arrived was, that this fluid differs much in its chemical properties from the saliva, with which many physiologists had confounded it. Notwithstanding the im- portance of the researches that have been cited, and the light thrown upon the subject, still it must be admitted that, in the pres- ent state of knowledge, we are unacquainted with the uses of the pancreatic juice. Secretion of the Bile. The liver is the largest gland in the body; it differs from all the other secretory organs still more in being constantly traver- sed by a large quantity of venous blood, besides the arterial blood sent to this as to every other part. Its parenchyma does not re- semble the other glands, and its secretions differ essentially from. all other glandular fluids. [When the liver is closely examined by the naked eye, it is found, according to Kiernan, to consist of small granular bodies, about the size of a millet-seed, of an irregular form, and present- ing a number of rounded, projecting processes upon the surface. These are called lobules or acini. When longitudinally divided, they present a foliated appearance, from their connexion with the hepatic vein, which, passing into the centre of each division, is named the intra-lobular vein. The exterior of each lobule is cov- ered by a process of the Capsule of Glisson, and its substance composed of the minute ramifications of the before-mentioned ves- sels, the spaces between which are filled up with a parenchyma composed of nucleated cells. The following figure, after Kier- nan, shows this structure; thus it will be seen that each lobule represents the essential character of the whole gland. Figure 46 shows the connexion of the lobules of the liver with the hepatic vein. (Fig. 46.) A is the trunk of the hepatic vein. B B B are the lobules de- pending from its branches, like the leaves of a tree, the centre of each being occupied by a venous twig; this is the intra-lobular vein. 460 NUTRITIVE FUNCTIONS. Below is a magnified view of the lobules of the human liver, with ramifications of the hepatic vein, marked A. B indicates the nucleated cells, composing the parenchyma of the gland, aa represented by Wagner. (Fig. 47.) Lobules of Human Liver. The lobules, when transversely divided, are found to present a somewhat pentagonal or hexagonal shape, rounded so as to form a series of passages or interlobular spaces. On these lie the branches of the vena porta, and of the hepatic vein, artery, and duct, from which are derived the plexuses that compose the lob- ules. Each lobule, when examined with the microscope, is seen to be apparently composed of numerous minute bodies, of a yel- low colour and of various forms, called by Malpighi acini. The vena porta, it will be recollected, is found by the convergence, of the veins, which return the blood from the chyloporetic viscera. —(Carpenter.) The following is a magnified horizontal section, after Kiernan, of three superficial lobules, showing the interlobular spaces, and the two principal systems of blood-vessels. (Fig. 48.) Horizontal Section of Hepatic Lobules. A A. Intra-lobular veins proceeding from the hepatic veins. B B. Interlobular plexus, formed by the branches of the portal veins.] The excretory duct of the liver terminates in the duodenum, OF SECRETION. 461 but before reaching this part it communicates, by means of a small duct, called cystic, with a small membranous sac, called the vesicula fellis, which is almost constantly filled with bile. The cystic duct is garnished with a small spiral valve, discovered by M. Amusat. There are few fluids which so materially differ from the blood as the bile. Its colour is greenish; its taste extremely bitter; it is viscid, stringy, sometimes transparent and sometimes clouded. It contains water, albumen, a substance called by chem- ists resin, a yellow colouring principle,* soda, and salts, viz., mu- riate, sulphate, and phosphate of soda, phosphate of lime, and ox- ide of iron. These properties are particularly found in the bile contained in the gall-bladder. That which passes directly from the liver, and which is called the hepatic bile, has never been an- alyzed. It is not of so deep a colour, is less viscid, and less bit- ter than the cystic bile. M. Lassaigne, who examined that extracted from a living dog, has not found it to differ from that taken from the gall-bladder. According to M. Thenard, 800 parts of the bile is composed of Water .... . 700. Green resinous matter . 15. Picromel . 69. Yellow matter . 00. Soda . 4. Phosphate of soda . . 2. Hydro-chlorate of potassa and soda 3.5 Sulphate of soda . 0.8 Phosphate of soda and ma smesia . 1.2 Traces of oxide of iron . . 00. M. Chevreul found in this fluid cholestrine. The result of a great number of experiments by Messrs. Tiede- mann and Gmelin is, that the bile in the human subject contains cholestrine, resin, picromel, oleic acid, a great quantity of matter soluble in water, colouring matter, mucus ; and undoubtedly, add these authors, many other substances. The formation of bile seems to be continual. Whatever may be the circumstances in which the animal is placed, if the orifice of the duct, called the ductus communis choledochus, be laid bare, we can distinguish this fluid passing drop by drop over the surface of the intestine. It appears that the gall-blad- der becomes filled when the stomach is empty and the abdom- inal pressure least. It has always appeared to me to be more distended at this time, but it does not lose all its contents when the stomach is full. The circumstance which contributes most to the expulsion of the bile is vomiting. I have often found it flaccid in animals that had died from vomiting, the effeets of poi- sons. But in no instance have I perceived indications of contrac- tility either in the gall-bladder itself or the hepatic or cystic ducts, * It is thought that the yellow colouring matter of the bile is the same as that of the se- rum and urine. 462 NUTRITIVE FUNCTIONS. notwithstanding I have tried upon these parts all those excitants which cause intestinal and vesical contractions. In birds these. parts are contractile. With respect to the manner in which the bile passes from the liver towards the gall-bladder, and^ accumulates so as to distend it, this appears to be owing to the great contraction of the ductus communis choledochus at the moment it pierces the walls of the duodenum. The bile, thus meeting with an obstruction to its free discharge, undergoes a reflux motion through the cystic duct to- wards the gall-bladder, where it meets no obstacle. This effect is produced even in the dead body; if we push gently an injec- tion through the hepatic duct, a part of the liquid passes into the intestine, and a part into the gall-bladder. It is probable that the spiral (spiroide) valve discovered by M. Amusat acts an impor- tant part, both in the entrance of the bile into the gall-bladder, and its discharge from that reservoir. The liver receiving both venous blood from the vena portae, and arterial blood by the hepatic artery, physiologists have anx- iously inquired which of these two bloods serve for the formation of the bile. Many have said that the blood of the vena portae, being more highly charged with carbon and hydrogen than that of the hepatic artery, was more suitable to produce the elements • of the bile. Bichat combated successfully this opinion ; he demon- strated that the quantity of arterial blood that arrived at the liver was more proportioned to the quantity of bile secreted than that of the venous blood; that the volume of the hepatic duct was not in proportion with the vena portae ; that the fat, a substance high- ly charged with hydrogen, was secreted with arterial blood. We do not take sides in this discussion; both opinions are equally des- titute of proof. Besides, nothing is more probable than that both kinds of blood may serve in the secretion. Anatomy seems to indicate it; for injections show that all the vessels of the liver, arterial, venous, lymphatic, and excrefory, communicate together. The bile concurs in digestion in a very useful manner, though the mode is unknown. In our ignorance relative to the causes of diseases, we attribute to the bile injurious properties which prob- ably do not exist. Secretion of Urine. The secretion to which we are now about to call the attention of the reader differs in many respects from the preceding. The fluid which is the result of it is much more abundant than that of any other gland ; and, instead of performing any farther uses in the economy, it is destined to be expelled. We are informed of the necessity of doing this by a peculiar sensation, which, like other instinctive phenomena of this kind, becomes very vivid and painful; if it be' not satisfied promptly, its retention is accompa- nied by the most troublesome consequences. There are few of the organs of secretion s6 complicated as that of the urine. It is composed of the two kidneys, the calices, the pelvis, the ureters, OF SECRETION. 463 the urinary bladder, and the urethra. The abdominal muscles also concur in the action of these different parts; the kidney's alone secrete the urine ; the others only serve the purposes of re- taining, transporting, and expelling it. [Organs destined to urinary secretion are found low in the scale of animals. The following figure is a representation of a ver- tical section of the kidney surmounted by the supra-renal cap- sule. (Fig. 49.) Vertical Section of Kidney. No. 1. The supra-renal capsule. No. 2. The vascular or corti- cal portion. No. 3. The tubular portion, consisting of cones. No. 4. The calices, receiving the apices of the corresponding cones. No. 5. The infundibula. No. 6. The pelvis. No 7. The ureter. The cortical part of the kidney is very vascular; the plexus formed by the tubuli uriniferi coming into the closest connex- ion with the sanguiferous capillaries of this part. This appears to be the principal seat at which the process of secreting the urine takes place, the tubuli uriniferi conducting the secreted fluid towards the ureters. As the tubuli pass towards the cortical portion, they increase in number by divarication, their diameter remaining the same. When they arrive at the cortical substance, their previous straight direction is changed, and they become very much convoluted. The closeness of the texture formed by their interlacement with the blood-vessels renders it difficult to obtain a clear view of their mode of termination. There seems, however, no doubt that they inosculate with each other, forming a plexus, with a free extremity here and there. But the number of these free or coecal extremities does not appear to be nearly equal to that of the uriniferous tubes themselves. Scattered through the plexus formed by the blood-vessels and uriniferous tubes, a number of little dark points may be seen with the naked eye, known as the Corpora Malpighiana. These, when examined by a high magnifying power, are found to consist of a convolu- 464 NUTRITIVE FUNCTIONS. ted mass of minute blood-vessels, somewhat resembling the con- volute masses of absorbents known as the lymphatic glands. It was at one time supposed that the uriniferous tubes arose direct- ly from these bodies; but the careful examinations of Miiller and Huschke have proved that the vascular bodies have no direct connexion with that system, being only capable of injection from the arteries or veins. Of their use nothing is positively known; it is evident, however, that they must have some special function, since they are found in the kidneys of all vertebrated animals. —(Carpenter.) (Fig. 50.) Portion of the Kidney in a New-born Infant, after Wagner. A. Of the natural size, a a. Corpora Mal- pighiana, as dispersed points in the cortical substance, b b. Papillae. B. A smaller portion magnified, a a. Corpora Malpighiana. 6. Tu- buli uriniferi. The walls of the tubuli uriniferi appear to be the parts in which the secretion takes place. When one of the coecal extremities is examined with a high magnifying power, its mucous membrane is found to be covered with a layer of nucleated cells, forming an epithelium. The following is one of these coecal extremities, from the kidney of an adult, magnified 250 diameters, after Wagner, showing the tesselated epithelium. (Fig. 52.) Extremities of Tubuli Uriniferi The cut on the opposite page (fig. 51) is a representation of a smal^portion of the kidney magnified sixty times, after Wagner. OF SECRETION. 465 (Fig. 51.) A is a coecal extremity of a tubulus uriniferus. B B. Recur- rent loops of tubuli. C C. Bifurcations of tubuli. D E F. Tu- buli, converging towards the papillae. G G G. Corpora Malpighi- ana, seen to consist of plexuses of blood-vessels connected with a capillary network. H. An arterial trunk.] r Nnn 466 NUTRITIVE FUNCTIONS. The kidneys are small in proportion to the quantity of fluid they secrete. They are generally surrounded with a large quantity of fat, and are situated on the sides of the vertebral column, before the last of the false ribs and the quadratus lumborum. Their parenchyma is generally composed of two substances: the exte- rior, which is very vascular, is called the cortical; the other part, called medullary or tubular, is arranged into a certain number of cones, the bases of which correspond to the surface of the organ, and the apices unite in a membranous cavity, called the pelvis. These cones appear to be formed by a large number of small hol- low fibres, which are excretory ducts of a particular kind, and are constantly filled with urine. There is no organ which re- ceives so much blood, in proportion to its volume, as the kidney. The artery is short and large, and arises directly from the aorta; it communicates very freely with the veins and tubular substance, as may easily be shown by injections of the coarsest kind, which, when pushed into the renal artery, pass into the veins and pelvis, after having filled the cortical substance. Filaments of the great sympathetic are the only nerves distributed to the kidney. The calices, pelvis, and ureters form together a canal, which passes from the kidney, where it embraces the papillae, and ter- minates in the bladder. This last organ is an extensible and con- tractile sac, destined to receive the fluid secreted by the kidney, and which communicates externally by a canal called the ure- thra ; this is long in man, but short in the female. The posterior extremity of the urethra in man is surrounded by the prostate gland, which has been considered by some anatomists a mass of mucous follicles. Two small glands, placed before the anus, pour out a particular fluid into this canal. Two muscles descend from the pubis towards the rectum, pass along the sides of that part of the bladder which terminates in the urethra, approach each other posteriorly, and thus form an arch which embraces the neck of the bladder, and raise or depress it. If we divide the pelvis of the kidney in a living animal, we can perceive the urine oozing out slowly from the papillae ; this fluid is deposited in the cavity of the calices, afterward in that of the pelvis, and gradually in the ureter, through which it at last pen- etrates to the bladder, into which it continues constantly to trick- le, as it is easy to perceive in persons affected by a deformity, called a retroversion of the bladder, in which the internal surface ef this organ is exposed to view. A slight compression of the pa- pillae forces the urine out in a considerable quantity, but instead of being limpid, as it is naturally, it is thick and turbid. It ap- pears, therefore, to be filtered by the hollow fibres of the tubular substance. The passage of the urine into the bladder through the ureters is not constant; at regular and short intervals, the ure- ters, dilated by the urine, open at their vesical orifice, and allow the urine to pass. Sometimes it enters in a small jet at first, but afterward gradually oozes in. Then for a few seconds the ure- ters and their orifices sink down, and the discharge of urine ceas- OF SECRETION. 467 es. Generally, the entrance of the urine into the bladder takes place during inspiration. Neither the pelvis nor the ureter being contractile, it is probable that the force which determines its prog- ress is partly that by which it is poured into the pelvis, and partly the pressure of the abdominal muscles; to which may be added, when the body is erect, the weight of the fluid.* Under the in- fluence of these causes, the urine is introduced into the bladder, and by degrees distends this organ; sometimes to a considerable extent, the extensibility of its different membranes permitting this accumulation.! Why does the urine accumulate in the bladder? why does it not immediately pass out by the urethra, or flow back into the ureters ? The answer, as respects the ureters, is very easy; these ducts pass for a considerable distance through the substance of the walls of the bladder. In proportion, therefore, as tne urine distends this organ, it flattens the ureters, closing them most ex- actly when it is abundant This effect takes place as well in the living as the dead body ; a liquid, or even air, pushed with great force into the bladder, cannot be introduced into the ureters. It is owing, then, to a mechanism analogous to that of certain valves, that the urine does not return towards the kidney. It is not so easy to explain the reason that the urine is not im- mediately poured into the urethra; many causes seem to concur in producing this effect. The walls of this canal, especially to- wards the bladder, tend continually to react upon themselves, and to efface its cavity. M. Amusat has demonstrated, by a series of very curious anatomical and physiological researches, that the membranous part of the urethra is formed externally by muscular fibres, and that these fibres are endowed with a very energetic contractility. I am satisfied of the accuracy of these facts. But the principal cause which prevents this effect is the contraction of the levatores ani muscles, which, either from the disposition in their fibres to shorten themselves, or from their contraction under the direct influence of the brain, press the urethra from below upward, thus bringing its walls in contact, and closing its poste- rior orifice. * As it is proved .that the heart and the elasticity of the arteries have a marked influence on the course of the blood in the capillaries and veins, may not these causes act upon the fluids in certain excretory ducts ? t Physiologists have often compared the introduction of the urine into the bladder to that of a fluid into a cavity with resisting walls, by a narrow, vertical, and inflexible ca- nal ; but the comparison is not exact. In the supposed canal, the fluid runs and presses continually the fluid contained in the vessel which receives it. The urine does not run in the ureter; it trickles, drop by drop, and in this respect its influence upon the distention of the bladder cannot be compared to that which is produced by the weight of a fluid. The abdominal pressure must have a great influence in the dilatation of the bladder by the urine. If the bladder and ureters be equally pressd, this cause will be sufficient-to intro- duce the urine into the bladder. Supposing the pressure to be equal in every part of the abdomen, if the surface of the pelvis of the kidney and ureters be superior to the bladder, the urine should enter easily into the last. But the abdominal pressure appears to be much weaker in the cavity of the pelvis than in the abdomen, properly so called. It is thus easy to conceive how the urine passes from the ureters into the bladder. However, the disten- tion of the bladder by the urine has its limits. When it is carried to such an extent that the organ contains more than a pound of urine, the distention stops, and the ureters, in their turn/become dilated from their inferior towards their superior part. 468 NUTRITIVE FUNCTION?. Excretion of the Urine. When the urine is accumulated in certain quantities in the blad- der, we feel a desire to expel it. The mechanism by which this is effected deserves particular attention, as it has not been always rightly understood. If the urine be not constantly passing out, this is not owing to any want of contraction in the bladder, for this organ has always a tendency to react upon itself. But, by the influence of causes that we shall now point out, the internal orifice of the urethra resists this with a force that the contraction of the bladder is incapable of overcoming. This condition of things is removed by the will; first, by adding to the contraction of the bladder that of the abdominal muscles; second, by relaxing the elevator muscles of the anus, which close the urethra. When this resistance is once overcome, the contraction of the bladder is sufficient for the complete expulsion of the urine which it con- tains ; but if the action of the abdominal muscles be added, the force and size of the stream is much increased. We can sud- denly stop the flowing of the urine by contracting the levatores ani muscles. The contraction of the bladder is not voluntary, though, by the action of the abdominal and levatores ani muscles, we can permit its contraction at pleasure. This contraction is sufficient to expel the urine; I have often seen dogs urinate after the abdomen was opened, and the bladder no longer exposed to the action of the ab- dominal muscles. If we detach the bladder with the prostate, together with a small part of the membranous portion of the ure- thra, in a male dog, in a few minutes the bladder will contract, and the urine be thrown out with a jet to a considerable distance, until entirely expelled. What urine remains in the urethra after the bladder is emptied is expelled by the contraction of the mus- cles called the acceleratores urines. Though the quantity of this fluid is very abundant, and though it contains many immediate principles not found in the blood, and which are, therefore, formed by some chemical action in the kid- neys, the secretion of urine is very rapid. During health the urine is of a yellow colour, more or less deep, its taste saltish, and a little acid, and its odour peculiar. It is composed of water, mu- cus, probably derived from the mucous membrane of the urinary passages, of other animal substance, uric acid, phosphoric acic[, lactic acid, muriate of soda and ammonia, phosphate of soda and ammonia, lime, magnesia, sulphate of potash, lactate of ammonia, and silex. The physical properties of the urine are subject to great variations. If we make use of rhubarb or madder, it be- comes of a deep yellow ; if we respire air loaded with the vapours arising from turpentine, or if we take this drug internally, the urine assumes an odour like violets ; every one knows the disagreeable odour of the urine after eating asparagus. Its chemical composition is equally variable. The more water we drink, the greater the proportion of water in the urine ; and the OF SECRETION. 469 reverse. The uric acid becomes abundant when the diet is very generous, while the person exercises but little; but this acid di- minishes,' and may even be made to disappear entirely, by the continued and exclusive use of non-azotic aliments, such as sugar, gum, and butter, &c. Some salts, when introduced into the stomach, even in small quantity, are found in a very short time in the urine. The extreme rapidity with which this is effected has given rise to the belief that there exists a direct communication from the stomach to the bladder; even at this time there are many persons of this opinion. For a still longer time it has been sus- pected that there was a duct passing from the stomach to the bladder ; but no such part has ever been demonstrated. Some have thought, but without adducing any proof of the fact, that this took place through the cellular tissue, by the anastomoses of the lymphatic vessels.. . Darwin having given to one of his friends a few grains ol the nitrate of potash, collected the urine at the end of a few hours, and then bled him. The salt was found in the urine, but eould not be recognised in the blood. Mr. Brande made a similar ob- servation with the prussiate of potash; he concluded that the cir- culation is not the only medium of communication between the stomach and bladder, but did not undertake to explain what this medium was. Sir Everard Home is likewise of the same opin- ion I have made some experiments with a wish to throw some light on this important question ; and I have found, first, that when we inject the prussiate of potash into the veins, or into those parts where it will be rapidly absorbed, as the intestines or serous cav- ities it soon passes into the bladder, where it may be recognised mixed with the urine; second, if the quantity injected be very ereat, its existence in the blood may be demonstrated by re- agents ; but if the quantity used be very small, it is impossible to detect its presence by any known method; third, the same thing takes place when we mix in a vessel the prussiate and blood; fourth, we can detect the existence of this salt in all proportions in the urine. There is nothing very remarkable, therefore, in the fact that Darwin and Brande could not find this substance in the blood, though its presence in the urine was distinctly perceived. With respect to those organs which transport the fluids of the stomach and intestines into the circulating system, from what has been already said in speaking of the lacteal vessels and the ab- sorption of the veins, it is evident that the veins absorb the fluids directly, and transport them to the liver and heart. The route which the fluids pass through, therefore, to arrive at the kidneys, is much shorter than is generally supposed; that is, through the Ivmphatic vessels, mesenteric glands, and thoracic duct* Experiment has given many results relative to the secretion _, ,___.,;„t, tn cPp some verv curious experiments on the secretion of urine, and * Those who wishJ.o see sjeve^^^^ ^ ^ & ^ ^ particular^on the variations or fa a h sician of Pisa, m the fifth volume of Thi jttnTde PhysllgieThese researches were continued for many years with a perse- verance worthy of Sanctorius. 470 NUTRITIVE FUNCTIONS. of urine that I ought not to pass over in silence. The removal of one of the kidneys of a dog is not followed necessarily by in- jury to its health. The most remarkable change is an increase in the quantity and promptitude with which the urine is secreted. If both be removed, death invariably follows in from two to five days. I have constantly observed, in these experiments, that the secretion of bile increases in an extraordinary proportion; the stomach and intestines become filled. It was observed by Messrs. Prevost and Dumas, that after the ex- traction of both kidneys, a considerable quantity of urea was found in the blood. Thus it is shown that this substance is not formed by the kidneys, as has been generally supposed, they merely separating it from the blood, where it is formed. This fact was verified by Messrs. Vauquelin and Segalas. He farther remarked, that the introduction of Urea into the. blood excited the secretion of the urine, so that he regards the urea as an excellent diuretic. In explaining glandular secretion, physiologists have given a loose rein to their imaginations. The glands have been succes- sively considered as sieves, filters, and fermenting vats. Bor- deu, and more recently Bichat, have attributed to their molecules a sensibility and peculiar motion, by which they elect from the blood which traverses them the particles proper to enter into the composition of the fluids they are destined to secrete.* Some have given to them atmospheres, departments; others have sup- posed them susceptible of erection, sleep, &c. But notwithstand- ing the efforts of many very eminent men, it must be acknowl- edged that we are at present entirely ignorant of what takes place in a gland when it acts. Chemical phenomena are neces- sarily developed. Many secreted fluids are acid while the blood is alkaline ; many of them contain immediate principles which do not exist in the blood, and which are formed in the glands; but the particular mode of these combinations is unknown. But we will not confound among these hypotheses of the ac- tion of the glands a very ingenious suggestion of Mr. Wollaston. This distinguished chemist, being under an impression that elec- tricity, even when very weak, might have a decided influence upon the secretions, had recourse to the following curious experi- ment. He took a tube of glass about two inches high, and about three quarters of an inch in diameter, and closed one extremity with a piece of bladder. He then poured into the tube a little water with 1.240 part of its weight of muriate of soda; he then moistened the bladder, placed it upon a bit of silver, and bent a piece of zinc wire so that one of its extremities touched a piece of metal, and the other penetrated into the tube to the depth of about one inch. At this moment the external face of the bladder indicated the presence of pure soda. There was, therefore, from this very weak action of the electric fluid, a decomposition of the * Bordeu acknowledges that this is a mere metaphorical mode of expression. Vidt Researches on the Glands. OF SECRETION. 471 marine salt, and at the same moment the soda separated from the acid, and penetrated through the bladder. Mr. Wollaston thinks that it is not impossible that something analogous takes place in the secretions. It will be perceived that, before this idea can be fully admitted, many other proofs must be required.* The discovery of M. Dutrochet of endasmosis and exosmosis may, no doubt, throw some light on the theory of secretion, but no decided result has been yet obtained; it has.only furnished some conjectures of doubtful probability. Many organs, such as the thyroid and thymus, the spleen, and the capsular renales, have been called glands by anatomists. Pro- fessor Chaussier has substituted for this denomination glandi- form ganglions. We are totally ignorant of the uses of those parts, as they are, in general, most voluminous in the foetus; it is thought that they perform some important function during this state, but there is no absolute proof of this. The works of phys- iologists contain a great number of hypotheses constructed for the purpose of explaining their functions. General Doctrines of Secretion. [When we recollect the vast variety of materials that compose the solids and fluids of the animal body; how essentially they dif- fer from each other in their mechanical and chemical properties; the solids varying in density from a mineral to a, mere jelly, the fluids from a bland halitus to the most virulent poison ; and when we recollect that all these different substances are ultimately de- rived from a single fluid, the blood, we at once perceive the dif- ficulties in which every inquiry must be involved which aspires to throw light on a subject so recondite and averse to all our knowledge and experience as these transformations. The vari- ous processes by which these alterations in the living body are effected have received the general denomination of secretion, by which is usually understood the operation of secerning or separa- ting the newly-formed substance from the blood. But though our knowledge on this abstruse and mysterious subject is, in the nature of the case, loose and imperfect, yet so intimately are these secretory processes connected with every vital phenomenon, both in health and disease, that it becomes practically important to form as just ideas as possible on this subject. The material from which all the solid and fluid parts of the body are ultimately derived is the blood; the instruments by which these transmutations appear to be effected are the nervous, vascular, and lymphatie systems and membranous structures, controlled by that unknown power, life. In our reasonings in +ne physical sciences, we refer all the changes which take place "in matter to the simple or combined effects of three powers. These are mechanical agency, chemical attraction and repul- sion or one or both of these powers modified by the circum- stance of life in organized bodies. The mechanical powers are * For the secretion of the semen and milk, see Generation. 472 NUTRITIVE FUNCTIONS. few, simple, and admit of great precision in their investigation. They refer to the forms and motions of considerable masses of matter, which thus come within the scope of our senses, and are, therefore, well understood. The chemical changes which take place in bodies appear to be dependant upon the influence which the atoms or minute particles of matter exert on each oth- er at insensible distances. These operations are too minute to come within the scope of our senses, and are, therefore, chiefly judged of by their results. But by examining them in this way, modern chemists have attained a great degree of precision re- specting the chemical changes which thus take place in the com- position of bodies. It is perfectly demonstrable that the most ex- traordinary transformations take place, not only in the chemical properties, but the physical characters of bodies, in consequence of chemical attraction and decomposition. The same elements, chemically combined in different proportions, produce substances so widely different from each other in their appearance and qual- ities, that it seems scarcely credible that any such relation can exist. Take, for example, a few of the most common chemical elements, oxygen, hydrogen, nitrogen, and carbon, and recollect the great variety of different substances that may be produced by these chemical elements combined in different proportions; wa- ter, atmospheric air, nitrous oxide, nitric acid, hydrocyanic acid, &c, &c. Many of the operations of living organized bodies are evident- ly referrible to mechanical and chemical laws similar to those that control dead matter. When we examine the physical arrangements of the various organs and systems which compose the human body, we perceive their admirable adaptation to secure every mechanical advantage. The more we study and the better we comprehend the general objects and minute details, the more we are surprised at the ex- quisite skill with which these objects are accomplished. In the circulation of the blood, the numerous fragments into which the osseous system is broken up and each fitted to the other, and in the arrangement of the muscles, we recognise the most striking and beautiful illustrations of those hydraulic and mechanical prin- ciples which philosophy inculcates. We cannot examine the mechanism of the eye, as connected with our knowledge of the properties and laws of light, without something of the same sort of admiration we experience on viewing some exquisite produc- tion of art. There is such an obvious adaptation of the most simple and effective means to produce a given end, that we can- not doubt what objects the designer proposed to accomplish. Reasoning, then, from those things which are palpable and may be # understood, to those which extend beyond the ken of our senses, we may legitimately infer that the same fitness exists between the structure and function of those parts which, from their mi- nuteness, transcend our senses and comprehension. Thus, though we can perceive no relation between the mechanical structure of the muscles and their power of contraction, yet there can be no OF SECRETION. 473 reasonable doubt that such relation exists, and so of many other organs. But these mechanical arrangements are of no avail with- out the superaddition of that unknown power, life, by which these mechanical powers and laws are put in action and modified. It is also obvious that many of the changes which take place in the living animal body are the results of chemical affinity and repulsion, modified by the same unknown, mysterious princi- ple, life. The changes which take place in the external form and internal constitution of bodies, so that they acquire new proper- ties, is believed to depend on certain attractions and repulsions which their elementary parts exert on each other. Now these changes are incessantly going on, both in living and dead bodies. But though the laws by which these changes take place in these two classes of bodies are analogous, they are not identical. Thus, all those substances appropriated to the support of the animal body, commonly called the ingesta, when once they have become absorbed into the system, come under a new series of chemical influences. Their elements still continue to attract and repel each other, thus forming new compounds, differing essentially in their properties ; but the nature of these attractions, and, of course, the new substances thus formed, are essentially different from what is observed in dead matter. But when death takes place, then the elements which compose the animal body are again reduced to the same physical laws which govern other dead matter, and a necessary consequence is a decomposition into their original ele- ments. Hence, in modern physical science, the expression living chemistry has been very appropriately introduced, referring to this manifest distinction. One of the most remarkable circumstances in the economy ot organized bodies, especially the more perfect animals, is the vast variety which their elements exhibit, both in their physical and chemical characters. The large surfaces are kept moistened, and in a state most suitable for performing their functions, by fluids exactly adapted to their circumstances. In the larger, close cavi- ties, as those of the cranium, thorax, and abdomen, a thin hahtus is constantly transuding from every point. The smaller, close cav- ities, as the joints, are kept lubricated by a fluid essentially differ- ent, and exactly adapted to their uses ; while those cavities which communicate with the atmospheric air, are covered by fluids dif- fering essentially from either. In health, these fluids are con- stantly deposited and taken away, and are not suffered to exist either in excessive or deficient quantity, so as to impede the func- tion of the parts in which they are formed. There are, again, other new substances, formed for certain specific purposes, and which have certain apparatus expressly appropriated to their formation, as the chyme, the chyle, the saliva, the gastric and pancreatic juice, the bile, the semen, the milk, &c, while the sol- ids themselves are undergoing a constant change and renovation. Now when we recollect that these numerous solid and fluid substances differ from each other essentially in their physical and O o o 474 NUTRITIVE FUNCTIONS. chemical qualities, we naturally inquire, From what source are they derived, and how are they produced? Does our knowl- edge of the properties and laws of dead matter afford us any clew as to the modes by which the living body, by its own inherent power, accomplishes these extraordinary changes ? It cannot be pretended that there is, at the present day, any generally-received theory of secretion. To arrive/ at a correct view respecting the present state of our knowledge on this sub- ject, it will be necessary to look back for a moment at those spec- ulations which have occupied the greatest space in the confidence of the profession. Through the whole history of speculative med- icine, we find one error uniformly prevailing. Physiologists, in all their attempted explanations of vital phenomena, have reasoned as if they must necessarily be the results of a single class of in- fluences or agencies. Whatever has happened to be the favourite topic of the philosophy of the day, has been assumed as the only power to which these vital phenomena were referrible. Thus, the mechanical and chemical sects and the animists are the three classes of speculative opinions which have exerted the greatest sway in the profession. The opinion was at one time almost universally received, that the secretions exist ready formed in the blood, and that they are separated from it by means of arteries of different sizes and forms, and going off at different angles from the main trunks. That the glands were mere filters, which only allowed their peculiar fluid to pass through. The effect of chemical agency was not admit- ted, but everything was referred to mechanical power. These were the opinions of Haller and others, who may be regarded as modern physiologists. But this hypothesis will not bear examina- tion. In the first place, we find among the secretions substances which have no resemblance to the blood, and which it can be proved do not exist ready formed in the blood. For example, the bile differs as much in its chemical composition from the blood, or any of its known elements, as it does in colour, taste, and appear- ance. The same remarks hold good, in a greater or less degree, in all the secretions. They differ not only from the blood, taken as a whole, but the parts into which it spontaneously resolves itself, and also those into which it may be artificially divided. In a word, it is impossible to extract from the blood a substance ex- actly resembling even the most simple of the secretions, as the exhalations or serous transudations, as they are called. But it is not meant by this to, deny that foreign substances are sometimes found in the blood. A free, oleagenous substancenas been alleged to have been found in the blood in cholera and some other dis- eases ; it has been said that the uric acid to exists in the blood of gouty persons, and that the formation of urinary and arthritic calculi may be prevented in these cases by avoiding aliments in which nitrogen abounds; while the presence of madder, indigo, &c, in the blood, appears to have been proved by chemical tests. Even the secretions haVe been occasionally observed preserving OF SECRETION. 475 some of their distinctive characters, and mixed mechanically with the blood; this has been particularly noticed with regard to the bile, the urine, and pus. The general belief, however, in these cases, is, that they have been absorbed after having been secreted by their appropriate organs. But even admitting, for the sake of argument, that all the secretions exist ready formed in the blood, and that they are separated by these small arteries and strainers; this does not get rid of the difficulty; it only throws it back, and keeps it out of sight, If we admit that all the secretions exist ready formed in the blood, the next question that arises is, Where does the blood get them ? We are thus thrown into a new di- lemma. But though the exclusively mechanical doctrines of secretion have necessarily fallen before' the progress of modern science, yet it has been more recently supposed that some of the secre- tions are formed by a mechanical operation, a mere filtering, while others undergo a chemical process. Thus, some are called serous exhalations, as the watery fluids formed on the surfaces of the serous membranes lining the close cavities, and in the cells of the-cellular tissue; and others, resembling them, called the pulmo- nary and cuticular transpiration, thrown out from the surfaces of the lungs and the skin. These are considered by some physiologists as consisting of the more serous or watery parts of the blood ex- haling or transpiring mechanically through openings in the tex- tures ; hence the name given to these fluids. At the same time, it has been perceived that the wax of the ear, the black pigment of the eye, the bile, &c, &c, which do not resemble any portion of the blood, require a much more elaborate process. The fluids called serous exhalations, and cuticular transpiration, resemble the serum of the blood. In very debilitated states, when the liv- ing fibre may be supposed to be in a very relaxed state, these fluids are often poured out in inordinate quantities. Thus, the serous exhalations are very apt to accumulate in the cellular tis- sue and close cavities in very enfeebled conditions, constituting dropsies ; one of the most invariable symptoms which mark the close of chronic diseases is the copious cuticular transpiration commonly called colliquative sweats; while in those acute dis- eases where the energies are suddenly and effectively broken down, as in the collapsed state of cholera, and in the article of death from whatever cause, a cold sweat is poured out from the whole surface of the skin. All these phenomena seem at first satisfactorily explained by considering them a mere transudation of the serum of the blood, or leaking out between the interstices of the tissues or small openings in the capillary arteries, and, there- fore, increasing with the relaxed state of the living fibre. But there is great reason to doubt whether any of the fluids formed by the living body are produced by a mere mechanical process. It has been shown, by the nicest chemical analyses, that these exhalations and transpirations differ in their composition essentially from the serum. The cuticular and pulmonary trans- 476 NUTRITIVE FUNCTIONS. piration are composed of the largest proportion of water, and the smallest of animal matter, of any of the secretions, except the aqueous and vitreous humours. It differs, however, from the se- rum, not only in containing much less animal matter, but also, ac- cording to Berzelius, in containing a free acid, the lactic, which is not found in the serum. Traces of iron were also found by The- nard in the pulmonary and cuticular transpiration, which do not exist in the serum. The fluids poured out by the serous mem- branes differ from the serum of the blood in containing a much smaller proportion of albumen. Thus these fluids, so essentially^ different from the serum, or any other part of the blood, in their physical characters and chemical composition, cannot manifestly be separated from that fluid by a mere mechanical arrangement, but are no doubt elaborated by distinct organs and peculiar pro- cesses. Still we are not authorized, from these facts, to infer that the mechanical arrangement does not constitute an essential circumstance in every secretory organ for the due performance of its functions. On the contrary, the moment the mechanical arrangement of the organ is disturbed, the process is proportional- ly rendered imperfect. This rule appears to hold true from the most minute and simple to the largest and most complicated organs. Thus, the derangement in the secretion of an organ is sufficient to raise a suspicion that a change has taken place in its mechanical structure. The accurate observations which have been made on this point is the foundation on which have been erected many of the most valuable improvements in the modern practice of physic. This has been most remarkable in the organs contained within the cavity of the chest; but every day is showing its applicability to the other organs. The great difference in the forms, sizes, and general arrange- ments of the different secretory organs is sufficient to show that the mechanical form is an important circumstance. While some are small and simple, others are large and loose, and complicated. We cannot doubt that the greater size of the latter, and all this display of apparatus, are for some important end ; nature is too eco- nomical in the expenditure of materials and power to use them unnecessarily. Compare, for example, the structure of the kid- ney with that of the testis. We can discover a manifest relation between the mechanical form of the former and its functions, it closely resembling a filtering machine. But when we trace in the testis the long, tortuous course of the blood-vessels, the infinite- ly delicate and complicated seminiferous tubes and excretory ducts, we can perceive no such relation, yet we cannot reasona- bly doubt that all this complex and delicate machinery is indis- pensable for elaborating this important fluid. The apparatus for forming the secretions is simple or complica4ed, large or small, supplied copiously or sparingly with blood, according to the na- ture of the secretion, the purposes for which it is supplied, and the quantity to be employed. We are, undoubtedly, quite ignorant of the ultimate structure of these organs, and can perceive no OF SECRETION. 477 more reason, e. g., that the liver should secrete bile, or the mammae milk, than the reverse. Nor is this surprising, for. after all, the structure of the glands does not appear to be much more incomprehensible to an enlightened mind than the apparatus of the chemist to one entirely ignorant of that science. If the mi- nute parts of the glandular apparatus could be unfolded to our senses, no doubt we should perceive that the mechanical arrange- ments were indispensable in facilitating the combinations and elaborating the secretions. This remark probably holds good in all the structures of the body, though, from the imperfection of our organs of sense, we cannot discover these relations. We cannot perceive anything in the structure of the muscles which indicates a power of shortening themselves with force, nor in the eye of imparting the sense of vision. Still, there can be no rea- sonable doubt that these vital phenomena ate, to a certain extent, dependant upon the ultimate mechanical arrangement of the or- gans. We can see in the relations which the muscles bear to the fixed and movable portions of the bones, that every mechanical advantage is secured for the purposes of locomotion, and that the obvious uses of the different parts of the eye are to delineate with great accuracy the pictures of objects which are presented to it upon the retina, though we cannot perceive any necessary rela- tion between such pictures and the sense of vision. Still, we are justified in believing, from analogy, that such relation does exist. If our organs of sense were more acute or more numerous, so that we could appreciate other properties of matter, it is not im- probable that we could clearly apprehend the fitness of the struc- ture of the muscles to contract, and of the retina to produce the sensation of vision. The general inference, then, to be drawn from these views and reasonings is, that though secretion and other important vital phenomena cannot, for a moment, be suppo- sed to be dependant exclusively on mechanical laws, yet that this is one of the indispensable circumstances connected with the pro- duction of these phenomena. The attempt to explain secretion and other vital phenomena by purely chemical laws is equally inconclusive and unsatisfactory. The objection to this hypothesis is, that the living animal body is assumed to be a sort of miniature laboratory, with its tests and re-agents ready for use. Like the exclusively mechanical doc- trines, it merelv throws the question back, does not resolve it. How and where, we naturally inquire, are these re-agents formed, even admitting their existence, if they are not formed by secre- From the middle of the last century, when Dr. Franklin suc- ceeded in demonstrating the identity of lightning and electricity, to the present day, the important influence exerted by this agent in the various operations of nature has become daily more op- vious. Modern investigations have greatly extended our knowl- edge of the relations of this agent, especially under the forms of what have been called galvanic and magnetic electricity. Yet, 478 NUTRITIVE FUNCTIONS. at present, we can scarcely be said to have done more than to have attained a glimpse of the magnitude of the subject. We have become acquainted with a number of facts which appear to indicate this as one of the essential agents concerned in the pro- duction of vital phenomena, especially secretion. Its power of producing muscular contraction, after the consciousness of the animal has ceased, has been long and familiarly known. The beautiful experiment of Dr. Wollaston, of decomposing the muri- ate of soda by means of a very small galvanic battery—one of the elements of the battery being a lady's silver thimble—has been alluded to. In a paper published by him in the Philosophi- cal Magazine, in which he described this experiment, he advances the hypothesis that the nature of the secretions depends upon the electrical state of the glands. Finding the urine acid, he supposes that this must be in consequence of the highly positive electrical state of the kidneys; while the bile, being alkaline, he attributes to the negatively electrical state of the liver. A moment's reflec- tion shows that these are mere gratuitous assumptions, resting on remote and loose analogies, notwithstanding the high authority of their author. The experiments of Dr. Wilson Philip on digestion in rabbits appear to bear more directly on this point, viz., the influence of galvanic agency in secretion. He first proved, by a number of direct experiments, that the power of digestion in the rabbit is im- mediately lost on dividing the par vagum. He next endeavoured to show that the process of digestion could be kept up after the division of the nerve, by causing an electrical current to pass through the distal portion of the divided nerve. The experiments of Dr. Philip are curious and interesting, but by no means author- ize the inferences he has drawn, viz., that nervous influence and galvanic agency are identical. This supposition is unsustained by his experiments, and in itself highly improbable. The blood being the material from which all the secretions are formed, its electrical state has therefore been particularly exam- ined, in the hope of throwing some light on this subject. A num- ber of facts have been observed which go to show that the gen- eration of animal heat is accompanied with certain electrical phe- nomena. Some facts of this kind are related by Humboldt and Berzelius, while Bellingeri asserts, from direct experiments, that the blood possesses a peculiar electricity, which it preserves inde- pendently of that of the atmosphere. He asserts as a result of di- rect observation, " That in gout, rheumatism, peripneumony, hy- drothorax, intermittent fevers, phthisis, and syphilis, the blood has a different electrical state."* But still a vast deal remains to be done before we can be jus- tified in drawing positive conclusions concerning the influence of electricity in the production of vital phenomena. It is not im- probable that many of the subtler processes of the animal body, * Vide Diet. Med. et Chir., t. xiv. OF SECRETION. 479 particularly secretion, digestion, the generation of animal heat, &c, will ultimately be found connected with electrical agency. But'this, in the present state of our knowledge, is mere specula- tion. . But although we are ignorant of the precise mode in which many of these changes occur, yet there can be no reasonable doubt that true chemical decompositions and recompositions take place in the living animal body. Gelatine, for example, enters largely into the composition of certain parts of the body, espe- cially in young animals. It abounds in the bones, tendons, espe- cially the skin, which is almost entirely gelatine ; yet, as has been already remarked, this material is not found in the blood ; it must, therefore, be produced from the blood by a chemical process. The same observation applies to adipose matter, so abundant in sbme animals. A still more remarkable illustration of this is fur- nished by some of the mineral substances found in the animal body. The urea, and urinary and biliary calculi, are undoubtedly formed in this way. The quantity of mineral substances, particularly lime, alkalies, iron, sulphur, carbon, phosphorus, &c, both in a separ- ate and combined state, appears to be much greater than is taken in by the food. This subject has been investigated by Vauquehn, Prout, Einhoff, Shrader, and Berzelius, who, after the most crit- ical analyses, have arrived at some surprising results. Vauque- lin, after the most careful observations on the composition of the egg-shells and excrement of fowls, and comparing them with the food, which was also carefully analyzed, concluded that a portion of the silex had disappeared, and new portions of lime formed. Dr. Prout made an elaborate series of experiments on the compo- sition of egg-shells and the substances contained within, and com- pared these with the earthy and saline substances found in the chick a,fter incubation. He appears to have been quite confound- ed at the results, and unequivocally asserts that the quantity of earthy matter found in the chick could not have existed m the soft parts of the recent egg. As we cannot, of course, admit the cre- ation of new matter in such cases, the only explanation that can be given of these surprising results, if we acknowledge their ac- curacy, is, that the living animal ,body possesses powers of decom- position and recomposition which transcend those discovered by art, by means of which substances supposed to be elementary are thus decomposed and recomposed. This tends to confirm the speculations of some distinguished modern chemists, who have suspected that even the metals were compound bodies, of which hydrogen is one of the ingredients. There is but one other mode of attempting to explain the phe- nomena of secretion, to which I shall briefly advert. It is that of the sect that has been called animists. They consider life as an independent existence, which controls all the functions of the body in a manner beyond our comprehension, and which it is therefore idle to attempt to explain. This was the doctrine of Stahl, and, to a certain extent, still prevails. It would appear that there are 480 NUTRITIVE FUNCTIONS. two circumstances that have contributed to give currency and permanency to the views of the animists. The first is the nu- merous absurd speculations with which the profession has been inundated, through its whole history, concerning vital phenom- ena. Men of sober sense, at last, turned with disgust from such idle and puerile speculations, and were glad to take refuge in any supposition by which they were protected from them. Thus the animists came at last to receive with coldness and dis- trust every attempt to explain the phenomena of animal life, or absolutely to repel them with the vague reply, " that it was a vi- tal action, and that we knew nothing about it." The second is a disposition to mingle certain theological dogmas with physiologi- cal doctrines. According to these views, the soul and the life are identical, and to undertake to ascribe the operations of the soul to physical causes is to incur the deep reproach of being a material- ist, without it being precisely understood what is meant by that expression. It appears to be chiefly owing to these two causes that the doctrines of the animists have found, and still continue to find, many supporters, though involving as great absurdities as they aim at avoiding. To assume that life produces all the changes observed to take place in the animal body, independently of physical causes and material agents, is contrary to reason and observation. That many of the phenomena exhibited by the living body are not un- derstood, and that some transcend our senses and comprehension, is no doubt true. But it is equally certain that many others are fully within the sphere of our understanding: this doctrine is also objectionable from its tendency to discourage independence of thought and a proper spirit of inquiry. From these premises the following conclusions respecting the process of secretion may be drawn: 1st. That this process is probably in no instance exclusively dependant upon mechanical agency; but that even the most sim- ple of the secretions, as the exhalations and cutaneous transpira- tion, are newly-formed substances, differing essentially, in their chemical properties, from any part of the blood, and, therefore, produced by a peculiar process. 2d. That although secretion is in no instance a purely me- chanical process, yet that the mechanical arrangement of every secretory organ constitutes an essential circumstance for the due performance of its office. Hence, in all instances where the se- cretory processes become morbid, we are led to suspect some derangement in the blood itself or in the mechanism of the secre- ting apparatus. In acute diseases, it is frequently slight, and easily restored; in chronic diseases, the perfection of the orga- nization is often permanently injured, constituting what is techni- cally called an organic disease, and is, therefore, incurable. 3d. That although, except in a very few instances, we cannot trace any relation between the mechanical form of the secretory organs and their functions, in consequence of the imperfection of OF NUTRITION. 481 our senses, yet there can be no reasonable doubt but that such relation exists. 4th. It is probable that every secretion is formed by what is called a process of living chemistry, the mechanical arrangement of the secretory organ being one of the indispensable conditions, and adapted to facilitate the formation of the new substance, and to conduct it off when formed. 5th. That the precise agents employed by the living body in accomplishing these decompositions and recompositions are un- known, though obviously most potent. The experiments of Drs. Wollaston and Philip, and other facts, render it probable that gal- vanic agency is one of these powers, though its mode of opera- tion is unknown, and even its employment for this purpose is by no means certain. 6th. That, though secretion is a vital process, and in many of its details transcends the power of our senses and comprehen- sion, yet that in others it is within the scope of our understand- ing, and is a proper object of investigation.*] OF NUTRITION. We know that the blood supplies the materials for all the se- cretions, internal and external; that its powers are preserved by general absorption, and by the chyle and drink. It remains for us now to examine what takes place jn the parenchyma of the organs and tissues during life; this is called nutrition. From the earliest periods of life to advanced old age, the body is constant- ly changing in weight and volume. The different organs and tissues present infinite varieties in consistence, colour, elasticity, and frequently chemical composition. The volume of organs aug- ments when they^re frequently in action ; on the contrary, their dimensions diminish much when they remain long in a state of repose. By the influence of one or other of these causes, their physical and chemical properties exhibit surprising variations; a great number of diseases produce, often in a very short time, very remarkable changes in the conformation and structure of a great number of organs. If we mix madder with the food of an ani- mal, during fifteen or twenty days, the bones present a red tint, which disappears when it is omitted. There exists, then, in the very substance of the organs, an in- sensible motion of their particles which produces all these modi- fications. It is this intestine motion, of the nature of which we are ignorant, to which we give the name of nutrition. This phenomenon, which the observing spirit of the ancients did not allow them to overlook, has been the object of many ingenious suppositions that are admitted by some at this day. It. is said, for example, that by means of nutrition, the whole body is renew- ed so that at any given moment it is not formed of a single par- ticle that composed it at some former period. Limits have even been assigned to this total renovation. Some have fixed three * Editor. Ppf 482 NUTRITIVE FUNCTIONS. years, others think it cannot be completed in less than seven ; but there is nothing to justify these conjectures ; on the contrary, some well-established facts appear to do away this idea. Everybody knows that soldiers, sailors, and savages are in the habit of colouring their skin with certain substances, which they introduce into the tissue of this membrane. The figures thus tra- ced preserve their form and colour during life, except under very peculiar circumstances. How does this phenomenon agree with this idea of renovation, which, according to authors, takes place in the skin ?* According to the supposition of which we have now spoken, it is understood, in the metaphorical language at present used in physiology, that the particles of organs cannot serve but a certain time in their composition ; and, being no longer suitable to com- pose the organs, they are then absorbed, and replaced by new molecules arising from the aliment. It may be added, that the animal substances which compose our excretions are the detritus of the demolished organs, and that they are principally composed of particles no longer capable of serving in the composition of the body, &c. Instead of discussing this hypothesis, let us examine the few facts which are ascertained on the subject of nutrition. In ob- serving the promptitude with which the organs change their chemical and physical properties by disease and age, it appears that nutrition is more or less rapid, according to their particular tissue. The glands, muscles, skin, &c, change their volume, col- our, and consistence with great rapidity; the tendons, fibrous membranes, the bones, and cartilages appear to have a much slower nutrition, as their physical properties change but slowly in consequence of age or disease. • If we take into consideration the quantity of aliments consumed in proportion to the weight of the body, it appears that the action of nutrition is much more rapid in infancy and youth than in the adult or advanced age ; it is accelerated by the action of the or- gans, and retarded by their remaining in a state of rest. Chil- dren and young persons consume more food than adults and old persons ; the last preserve their faculties with a very small quan- tity of aliment. All exertions of the body render a more abun- dant and nutritious diet necessary; a state of perfect repose, on the contrary, will permit a prolonged abstinence. The blood appears to contain the greater part of the principles necessary to the nutrition of the organs ; the fibrine, the albumen, the fat, salts, &c, which enter into the composition of the tissues, are found in the blood. They appear to be deposited in their pa- renchyma at the moment when the blood passes through them; * The recent employment of the nitrate of silver, internally, in the treatment of epilep- sy, has furnished a new phenomenon of this kind. After this remedy has been used for several months, the skin of many patients has become of a grayish-blue colour, probably owing to this salt being deposited in the tissue of this membrane, where it is placed in im- mediate contact with the air. Several individuals have remained in this state for many years, without the colour being diminished. In others, it has by degrees diminished, and disappeared at the end of two or three years. OF NUTRITION. 483 the mode of this deposition is entirely unknown. There exists an evident connexion between the activity of the nutrition of an organ and the quantity of blood it receives. The tissues, the nu- trition of which is rapid, have large arteries; when the action of an organ has determined an increased nutrition, the arteries and veins grow larger. There are many immediate principles enter- ing into the composition of organs which are not found in the blood ; such are uric acid, gelatine, &c. They are formed at the expense of the other principles in the parenchyma of the organs by a chemical action, the mode of which is unknown, but which is not less real, and must necessarily have an effect upon the development of heat and electricity. Since the nature of the different tissues of the animal economy has been ascertained by chemical analysis, we know that they all contain a large portion of azote. Our aliments being, also, com- posed in part of this simple substance, it was probable that the azote of the organs was derived from them ; but many respectable authors think that it arises from respiration, and others that it is en- tirely formed by the influence of life. Both these opinions are sup- ported particularly by the example of herbivorous animals, which feed exclusively on substances not containing azote, or the history of certain nations, whose inhabitants live entirely on rice and maize ; or that of negroes, who live for a long time upon sugar; and, finally, on what is said of caravans, who, in traversing the desert have little other food for a long time than gum. If these facts prove, indeed, that men are capable of living for a long time without azotic aliments, it would seem necessary to acknowl- edge that the azote of the organs has some other origin than the aliments. But, in fact, nearly all the vegetables employed for the nutrition of man and animals contain more or less azote. For example, the raw sugar eaten by the negroes is composed of it in a considerable proportion ; with respect to those people who are said to live on rice and maize, it is well known that they add to this diet milk and cheese ; now cheese, of all the immediate nu- tritive principles, has the most azote. It occurred to me that we might acquire more exact notions on this subject by submitting animals, for a sufficient period, to a par- ticular diet, the chemical composition of which should be deter- minate and rigorously pursued. Dogs were very proper for these experiments, as, like man, they are nourished by vegetable and animal substances. Every one knows that a dog can live for a long time on bread alone; but from this fact nothing can be con- clusively inferred relative to the production of azote in the animal economy, for the gluten contained in the bread abounds in azote. To obtain a satisfactory result, it would be necessary to feed one of these animals with a substance considered nutritious, but which does not contain azote. With this intention, I put a dog, about three years old, fat and healthv, upon a diet exclusively of pure, refined sugar, with dis- tilled water for drink; he had them both without any limit. For 484 NUTRITIVE FUNCTIONS. seven or eight days he appeared to be very well; he was spright- ly, ate with avidity, and drank as usual. He began to grow thin the second week, although his appetite was good, and he ate six or eight ounces of the sugar in twenty-four hours. His alvine excretions were neither frequent nor copious, and the urine was in sufficient abundance. The emaciation increased in the third week; the strength diminished, the animal lost its spirit, and its ap- petite became less. At this period there occurred, first upon one eye and then upon the other, a small ulcer on the centre of the transparent cornea; it augmented rapidly, and at the end of a few days it was about a line in diameter, its depth increasing in the same ratio; the cornea became soon perforated, and the humours of the eye discharged. This singular phenomenon was accompa- nied with an abundant secretion of the glands about the eyelids. In the mean time the emaciation continued to increase, and the strength to diminish, and though the animal ate daily three or four ounces of sugar, its debility became so great that it could neither chew nor swallow ; of course, every other motion was impractica- ble. It expired on the thirty-second day of the experiment. I exam- ined the body with every possible precaution ; there was no fat to be found ; the muscles were reduced more than five sixths of their ordinary volume; the stomach and intestines were much dimin- ished in size, and strongly contracted. The gall and urinary bladders were distended by the fluids peculiar to them. I re- quested M. Chevreul to examine them ; he found them possessing nearly all the characters belonging to the urine and bile of her- bivorous animals; that is, the urine, instead of being acid, like that of carnivorous animals, was sensibly alkaline, not exhibiting any trace of uric or phosphoric acid. The bile contained a con- siderable proportion of pycromel, a substance peculiar to the bile of the ox, and in general of all herbivorous animals. The excre- ments were also examined by M. Chevreul; they contained very little azote, though they ordinarily exhibit much of this substance. Such a result deserved to be verified by new experiments ; I was therefore induced to submit a second dog to the same regi- men, namely, sugar and distilled water. The phenomena were similar to those just described, except that the eyes did not begin to ulcerate until the twenty-fifth day, and the animal died before the ulcer had penetrated into the cavity of the eye, as occurred in the dog that was the subject of the first experiment. In other respects, the same emaciation and debility, followed by death on the thirty-fourth day, occurred; and on opening the body, the same state of the muscles and abdominal viscera, especially the same characters in the excrements, bile, and urine, were discov- ered. A third experiment afforded exactly similar results • and I was therefore induced to conclude that sugar alone is incapable of nourishing dogs. It was interesting to determine whether the defective nutri- tious qualities were peculiar to sugar, or whether they existed in common with other non-azotic substances, generally esteemed OF NUTRITION. 485 nourishing. I took two dogs, young and vigorous, but small in size; I gave them for food very good olive oil and distilled wa- ter, as their constant diet They appeared to be perfectly well for about fifteen days; after which they experienced a series of symptoms similar to those related of the animals that were fed on sugar No ulceration of the cornea, however, took place, but they died on the thirty-sixth day of the experiment: they pre- sented a similar state of the organs ; and in the composition of the urine and bile, the same phenomena as in the preceding cases. Gum is another substance which does not contain azote, but is generally considered nourishing; we might presume that it would let like sugar and oil, but it seemed desirable to determine this by direct experiment. With this view, I fed several dogs upon gum, and the phenomena I observed did not sensibly differ from those of which I have already given an account. I have recently repeated the experiment upon a dog with butter, an animal sub- stance destitute of azote. Like the animals in the preceding cases, he at first supported tnis diet very well, but at the end of fifteen davs he began to lose his flesh and strength. He died on the thirtv-sixth day, although, until the thirty-second, I gave him this food'as freely as he would eat it, and though he continued to ea until two days before his death. The right eye of this animal exhibited an ulcer of the cornea, similar to that mentioned to have taken place in the animals fed upon sugar. On opening the body, the same modifications of the bile and urine were noticed Al- though the nature of the excretions of these animals showed that thev had digested the substances which they had eaten, I was de- sirous of satisfying myself more positively on this point For this pZose, after having fed several dogs upon oil, gum or sugar, I opened them, and found that these substances were reduced into aTrticular chyme, and that they afterward furnished an abun- dant ehvfe That which came from the oil was of a white, milky nnnearance- the chyle produced by the gum or sugar was trans- parent and more watery than that of the oil. It is evident there- Fore that if these different substances do not nourish the body, it cannot be attributed to their not being digested. S^nce the publication of these facts, in the first edition of this work I have Observed others not less important, which show how limited our knowledge still is on the subject of nutrition. A dog was allowed to eat pure wheaten bread and drink com- mon wSeT at will. He died within fifty days, with all the signs *^™&^^X^<« munition bread; his "^S^J^ ?e°d°dwith a single substance, as wheat, bariey oats?cabbage, carrots, &c, will die, apparently from m- S?nn within a fortnight, and sometimes much sooner But if K^SStL*" beg given together, or after short intervals, thI ^i^ri^ afterward boiled it in water, be- 486 NUTRITIVE FUNCTIONS. cause he refused the first; the animal lived only fifteen days. The last days he constantly refused to eat the rice. A cock was ted on boiled rice for several months, and preserved its health. Dogs fed exclusively with cheese, and others with hard eggs, lived for a long time, but became weak and emaciated ; lost their hair, showing imperfect nutrition. The following is one of the most remarkable facts that have come under my observation. If an animal has lived for a certain time upon a substance which of itself cannot nourish it, as, for example, wheaten bread for forty days, it will be useless, after that time, to restore to it its ordinary diet and regimen. The an- imal will eat the new aliments with avidity; but it will continue to emaciate, and death will ensue with as much certainty and as soon as if the original exclusive diet had been continued. The most general and important consequence deducible from these facts, and which ought to be followed up and examined, is, that diversity and multiplicity of aliments is a very important hy- gienic rule. This is indicated by our instincts, and the variations that the seasons bring in the nature and kind of aliments. Messrs. Edwards and Balzac, in their interesting researches to decide the difficult question whether gelatine extracted from bones should be used as aliments by the poor classes, have arrived at results confirmatory of what has been said above. Bread alone does not nourish dogs, as we have already remark- ed ; but is this because it does not contain enough of the azotic principle ? To remove this difficulty, authors have added to the bread pure gelatine of good quality. But this is not found suffi- ciently nourishing to support life. It is necessary to add to the mixture a small proportion of the sapid substance of meat (osma- zome), that the nutritive process should be perfect. The experiments made by me on the fifth pair of nerves have led to some singular results connected with the nutrition of the eye. If the trunk of this nerve be divided in the cranium, within twenty-four hours after the section the cornea becomes clouded, and a pearl-coloured spot formed. At the end of forty-eight hours, this part becomes completely opaque, the conjunctiva and iris inflamed. A turbid fluid is deposited in the anterior chamber of the eye, and false membranes cover the internal face of the iris ; the crystalline and vitreous humour begin to lose their trans- parency, and in a few days it disappears entirely. Eight days after the section of the nerve, the cornea becomes detached from the sclerotica, and the humours of the eye, which remain liquid, escape by the opening. The organ diminishes in volume, be- comes atrophied, and ultimately becomes a sort of tubercle filled with cheesy matter. Thus it appears that the nutrition of the eye is under the control of nervous influence. The same remark ap- plies to the lachrymal gland, which receives special branches from the fifth pair, by the name of lachrymal nerve. This gland becomes atrophied and deteriorated, like the eye. Its functions, the secretion of tears, are abolished immediately after the section of the nerve distributed to it. OF ANIMAL HEAT. 487 The action of the organs develops their nutrition; repose re- tards it, and complete inaction stops it in some. This will be proved by the following experiment. Place the eye of a pigeon in such a situation that it cannot act; at the end of fifteen days it will be in.a complete state of atrophy. We see analogous effects in man. But generally a long timo passes before atrophy of the optic nerve is apparent, and most frequently it is confined to the anterior part, at the decussation of the nerves. < A great number of tissues in the economy do not appear to un- dergo the process of nutrition, properly so called; for example, the epidermis, the nails, the hair, the teeth, the colouring matter of the skin, and perhaps the cartilages. These different parts are really secreted, either by particular organs, as the teeth and hair, or by parts which perform at the same time other functions, as the nails and epidermis. These parts seem to be formed to pre- vent the friction of foreign bodies, and are renewed proportion- ally ; when completely removed, they are reproduced. It is a singular fact, that they continue to grow for several days after death; we have had occasion to mention a similar phenomenon respecting the mucus. Certain substances, particularly iodine, appear to have a marked influence upon nutrition. Their use ac- celerates or diminishes it; these opposite effects are obvious, and merit special attention. After these few observations on the prin- cipal phenomena of nutrition, it will be proper to examine a very important phenomenon, which appears to be intimately connected with nutrition and respiration; I refer to the production of heat in the human body. OF ANIMAL HEAT. A dead body, which does not change its state when placed in the midst of other bodies, soon acquires the same temperature, in consequence of the tendency of caloric to arrive at an equilibri- um. The human body acts differently: when surrounded by bodies warmer than itself, it preserves, during life, a lower tem- perature ; when surrounded by bodies of a lower temperature than itself, its temperature remains more elevated. There is, then, in the animal economy, two distinct and different properties; the one producing heat, and the other cold. Let us examine these two properties, and inquire, in the first place, how heat is produ- ced. The principal, or, rather, the most evident cause, is respira- tion. Experiment demonstrates to us, in fact, that the blood be- comes heated about one degree in passing through the lungs; and as it is carried from the lungs to every part of the body it carries everywhere warmth, and imparts it to the organs. We have already seen that the venous blood is a little colder than the arterial. This development of heat in respiration appears to arise, as we have already observed, from the formation of carbonic acid, whether this takes place directly in the lungs or in the parenchy- ma of the organs. The very beautiful experiments of Lavoisier 488 NUTRITIVE FUNCTIONS. and Laplace lead to this conclusion: they placed in a calorime- ter animals, and compared the quantity of heat produced with the quantity of carbonic acid formed in a given time ; within a very small proportion, the heat produced was such as would ne- cessarily be evolved from the quantity of carbonic acid formed. The experiments of Messrs. Brodie, Thillaye, and Legallois, also prove that, if the respiration of an animal be obstructed, either by placing it in a fatiguing posture, or in making it respire artificially, its temperature is diminished, and the quantity of car- bonic acid formed less. In those diseases where the respiration is accelerated, the animal heat is augmented, except under par- ticular circumstances. Respiration is, therefore, a centre from which the animal heat is developed. Science has attained to considerable precision respecting the production of animal heat. M. Despretz has made numerous ex- periments on the comparison of the heat emitted by animals and the heat disengaged by the combustion that takes place in the sub- stance of the lungs. It appears now to be well ascertained that four fifths of the heat in herbivorous animals is produced by res- piration, and three fourths in carnivorous and birds. The lungs, then, are the principal source of animal heat, as was indicated by the trials of Lavoisier and Laplace ; but, in these es- says, the comparison had not been made on the same animal. A Guinea-pig had furnished carbonic acid, and another animal of the same kind was used to measure the heat. It was necessary, there- fore, to make numerous and precise experiments, so as to leave no uncertainty as to the office executed by the lungs in this important phenomenon. It was this which induced the Academy of Scien- ces to propose this as a prize question, for which M. Despretz was the successful competitor. We shall only refer to the physiologi- cal results of his work. The following points appear to be established as results of these experiments: 1st. That respiration is the principal cause of the development of animal heat. 2d. That, besides the oxygen consumed in the formation of carbonic acid, a considerable quantity, in addition, at the same time disappears. It has been generally supposed that it is used in the combustion of hydrogen; but this explanation is not directly proved. 3d. That there is an exhalation of azote during the respiration of mammiferous, carnivorous, and frugivorous animals and birds ; and, generally, that the quantity of azote exhaled is proportioned to the quantity of oxygen consumed in respiration. In considering this as the source of heat in the animal body, we see that the caloric must be distributed unequally to the different parts of the body. Those parts which are most distant from the heart, or receive less blood, or which cool the easiest, must be gen- erally colder than those which present a contrary arrangement. This, in fact, is found to be actually the case. The limbs are colder OF ANIMAL HEAT. 489 than the trunk; they are often found at 88° or 90° Fah., and even less, while the cavity of the thorax approaches 104°. But the ex- tremities have a considerable extent of surface in proportion to their mass ; they are more distant from the heart, and receive less blood than most of the organs of the trunk. From the extent of their surface, and their distance from the heart, it is probable that the feet and hands would have a still lower temperature than what is observed generally, if these parts did not receive a large quantity of blood. The same disposition exists in all the external organs, the surfaces of which are very extensive, the nose, carti- lages of the ears, &c.; their temperature is higher than would be anticipated from their surface and distance from the heart. But, notwithstanding this foresight of nature, the parts with large surfaces lose their caloric more easily, and are not only habitually colder than the rest, but frequently experience consid- erable chills. The temperature of the hands and feet is frequently reduced, in winter, much below that of the neighbouring parts; this is the reason why we expose them the more freely to the fire. Among the means we instinctively use to prevent or remove the cold, are running, walking, leaping, &c, which accelerate the cir- culation ; and blows and pressures upon the skin, which draw into the tissue of this membrane a large quantity of blood. Another method, equally efficacious, is diminishing the surface in contact with the body which conveys away the caloric, as flexion of the different extremities upon each other, or placing them in contact with the trunk. Children and weak persons often adopt this when they lie down ;* for this, among other reasons, it is improper to dress children in swaddling clothes when they are to lie down in the cold. Our clothes preserve the heat; for the materials which compose them, being bad conductors of heat, do not allow it to escape from the body. ,. • c u From what has been said, it appears that the combination of the oxygen of the air with the carbon of the blood is sufficient to ex- plain most of the phenomena which occur in the production of animal heat; but there are some which, if real, cannot be explained in this way. It has been observed by persons worthy of belief, that, in certain local diseases, the temperature of the part diseased becomes higher than that of blood taken from the left auricle by several degrees. If it be so, the continual return of the arterial blood will not be sufficient to explain this increase of heat. The following researches were made by myself with a very delicate thermometer, and in no instance was the temperature of the in- flamed part above that of the blood. In one instance the diseased hand was eight or ten degrees above that of the sound hand, but nevertheless it was below that of the blood. According to M. Despretz, under the most favourable circumstances, and then only in herbivorous animals, respiration furnishes not more than 89 per centum of the animal heat, while in carnivorous animals it * See Memoir of Mr. Bies, in the Journal de Medicine, annee 1817. Q, o. a 490 NUTRITIVE FUNCTIONS. is not more than 80. Hence it is manifest that there are other sources of heat in the animal economy. They are probably connected with the processes of secretion, nutrition, and friction of the different parts on each other, which are modified in dis- eased parts. There is nothing forced in this supposition; for chemical combinations generally give rise to changes of tempera- ture, and we cannot doubt that, both in secretion and nutrition, combinations of this kind take place in the textures of the organs. By means of these two sources of heat, life may be preserved, though the body be exposed to a very low temperature, as that of winter in polar regions, where the thermometer often falls to 108° or 109° below zero. In general, we support with difficulty such excessive cold; and it often happens that those parts which are cooled the soonest freeze and mortify: this was experienced by many of the soldiers in the Russian war. However, as we are capable of resisting easily a low temperature, it is evident we possess the power of evolving heat to a great degree. That of producing cold, or, in more precise terms, of resisting heat, is more limited. In tropical countries, it has often happened that men have died suddenly, apparently from the heat, when the thermometer has risen to 120° Fahr. But our power of resisting heat is by no means limited to this. Messrs. Banks, Blagden, and Fordyce exposed themselves to a temperature of nearly 257°, and found that their bodies preserved nearly their ordinary tempera- ture. The more recent experiments of Berger and Delaroche have shown that the heat of the body could be raised by these means several degrees. It is not necessary, even for this effect, that the surrounding temperature should be very high. Having placed themselves in a stove at 119°, their temperature was raised about three degrees. M. Delaroche, having remained sixteen minutes in a dry stove, at 176°, found an increase of 4° in his per- son. Franklin, to whom the physical and moral sciences are indebt- ed for many important discoveries and ingenious observations, was the first who explained how the body resists excessive heat. He showed that this was the effect of the co-operation of the pul- monary and cutaneous transpiration, and that in this respect the bodies of animals resemble porous vases called alcarrazas. These vases, used in warm countries, allow the water they contain to ooze out, and thus to keep their surfaces constantly wet, from which arises a rapid evaporation, which cools the fluid they con- tain. To confirm this important fact, M. Delaroche placed ani- mals in a warm atmosphere saturated with humidity, so that evap- oration could not take place. These animals could not support but a moderate degree of heat, and became warmed as if they had no means of cooling themselves. It is thus placed beyond doubt that cutaneous and pulmonary evaporation are the causes by which man and animals resist a great degree of heat. This explanation is still more confirmed by the great loss of weight that the body undergoes when it is exposed to a high temperature. OF GENERATION. 491 From the facts which have thus been exposed, it is evident that the authors who have represented animal heat as fixed are very far from the truth. To judge correctly, it is necessary to take into consideration the temperature and humidity of the surround- ing atmosphere. It is also necessary to consider the temperature of the different parts, and not to judge of one by that of another. Few observations have been made on the temperature peculiar to the human body; Messrs. Edwards and Gentil have most re- cently investigated the subject. These authors have remarked, that the place most favourable to judge of the heat of the body is the armpit. They have remarked a difference of nearly a de- gree between the heat of a young man and that of a young girl; the hand of the last presented a temperature somewhat less than 98° ; that of the young man was nearly 99°. The same authors have observed remarkable differences in the heat of persons of different temperaments. There are diurnal variations ; the tem- perature varies two or three degrees from morning to evening. In general, this subject requires farther investigation. CHAPTER XIX. FUNCTION OF GENERATION. The functions of relation and nutrition are necessary to the ex- istence of the individual; but, like all other animals, man is called on to exercise another very important function, the reproduction of his species. In its object, generation differs very essentially from the functions of relation and nutrition; but it differs still more essentially in this, that the organs which co-operate in it do not exist in the same individual; this constitutes the principal dif- ference between the sexes. Apparatus of Generation. It is composed of the organs proper to man, and those peculiar to the female. Organs of Generation in Man. These organs are, the testicles, vesiculee seminales, prostate, glands of Cowper, and penis. ' The testicles are two in number; the cases related by authors who assert that they have seen three, and even four, are very doubtful. Their form is ovoid, and their size inconsiderable; their parenchyma consists of an infinite number of small vessels folded and rolled upon themselves, called tubuli seminiferi, and are directed towards a point of the surface called the head of the epididymis. Here they meet and anastomose, at the same time 492 FUNCTION OF GENERATION. diminishing in number, and finish by forming a convoluted canal called the epididymis. It soon leaves the organ, when it receives the name of vas deferens. It then rises up towards the inguinal ring, plunges into the pelvis, and arrives at last at the inferior and an- terior part of the bladder; there it communicates with the vesicu- lae seminales, and the prostatic portion of the urethra. [The testis is evidently a glandular body, and in its tubular structure resembles the kidney. It .consists of several lobules, which are separated from each other by processes of the tunica albuginea, that pass down between them, and also by an extreme- ly delicate membrane (described by Sir Astley Cooper as the tu- nica vasculosa), consisting of minute ramifications of the spermat- ic vessels, united by cellular tissue. Each lobule is composed of a mass of convoluted tubuli seminiferi, throughout which blood- vessels are minutely distributed. The lobules differ greatly in size, some containing one, and others many tubuli. The total number of the lobules is estimated at about 450 in each testis, and that of the tubuli at 840. The convolutions of the tubuli are so arranged that each lobule forms a sort of cone, the apex of which is directed towards the rete testis. It is difficult to trace the free extremities of the seminiferous tubes, owing to the frequency of their anastomoses with each other. In this respect, therefore, the structure of the testis closely accords with that of the kidney. The diameter of the tubuli is very uniform in the natural condi- tion, not exceeding from the yy^th to the —th. part of an inch; but when injected with mercury, they are distended to nearly double that size. The following is a "delineation of the human testis injected as completely as possible with mercury, after Louth. —(Carpenter.) A A. Lobules formed by the seminiferous tubes. B. The OF GENERATION. 493 rete testis C C. The vasa efferentia. D. Flexures of the effer- ent vessels passing to the head of the epididymis, marked E E. F F. The body of the epididymis. G. Appendix. H. The Cau- da. I. The vas deferens. . . When the tubuli seminiferi have reached within a line or two of the rete testis, they are no longer convoluted; several are united together into tubes of a larger diameter, which enter the rete testis under the name of the tubuli recti. The rete testis consists of from seven to thirteen vessels which run in a waving course, anastomose with each other, and again divide. The accompany- ing figure is a plan of the structure of the testis and epididymis. (Fig. 54.) D A A. The seminiferous tubes. A* A*. Their anastomoses. The other references as in the last figure.] The parenchyma of the testicle is enveloped by a strong fibrous membrane; it is also covered, first, by a serous membrane called meT4a vaginalis testis, which in the foetus makes a part of the Deritoneum ; second, by a muscular membrane which is capa- ble of^efevatSg the testicle, and applying it against the ring; *w ThliZTdartos a laver of loose cellular tissue, which appears ^Sa^rtV a rugous skin of <^^co^hig forms the scrotum, and possesses the property of contracting like ^^^^^^^ by a small artery de rived from the aorta, near the emulgent arteries. The veins of [his orgarTare large, tortuous, and numerous; have frequent anas- omosegs and have together received the name pampiniform bod- r Afthough the sensibility of the testicle is very great, it does noi appear fhat any nerve can be traced to it either from the ^The'naCet^ulae seminales has been given to two small cel- lularbodtes below the basfond of the bladder, and which appear • 494 FUNCTION OF GENERATION. to be destined to contain the fluid secreted by the testicle. Their walls are thin, covered internally by a mucous membrane, and externally by a fibrous coat; we do not know whether the inter- mediate membrane is or is not contractile. The anterior extrem- ity of these small vesicles communicates with the vas deferens and Urethra by a very short and narrow canal called the ejaculator. M. Amusat has ascertained, by a careful and delicate dissec- tion, that the vesiculae seminales are formed by a narrow duct of considerable length folded upon itself, and that its folds are held together by cellular tissue, like the spermatic ducts. The penis is the only part of the male organs of generation which remains to be described. It is formed by the cavernous bodies, the spongy portion of the urethra, and the glans penis. The cavernous bodies principally determine the form and dimen- sions of the penis. They commence on the internal part of the rami ischii, approach each other, and soon unite to form the body of the penis. They are separated from each other by a fibrous partition pierced with several openings; their external membrane is fibrous, thick, hard, and very strong. Their interior consists of laminae crossing each other in various directions, which togeth- er form a sort of sponge, in which the blood is extravasated. The urethra and glans, which are also essential parts of the penis, have a similar structure, but are not surrounded by a fibrous membrane. Six arteries are distributed to the penis ; this part also receives many nervous filaments, arising from the nerves of the sacrum. The genital organs in man really consist of but one apparatus of glandular secretion, of which the testicles are the glands, the vesiculae seminales the reservoir, and the vas deferens and urethra the excretory duct. This secretion is indispensable for generation. We give the name of semen to the fluid secreted by the testicles. The small volume of these glands, the number and tenuity of the spermatic ducts, the small quantity of blood carried by the sper- matic arteries, and the length and extreme narrowness of the vas deferens, render it probable that the quantity secreted is very small, and that it is propelled towards the vesiculae seminales very slowly. It is probable, also, that the secretion is constant, but is increased by venereal excitement, the use of certain aliment, and the frequent indulgence of the venereal appetite. It is ex- tremely difficult to explain how the semen is made to traverse the tubuli seminiferi, epididymis, and vas deferens. Perhaps it may be the effect of capillary attraction; an idea which appears to receive some support from the small size of these parts, and thickness and strength of their walls. It is somewhat easier to understand how the semen, having arrived at the extremity of the vas deferens, can penetrate into the vesiculae seminales. The ejaculatory ducts embraced, together with the neck of the bladder, by the levatores ani muscles, will resist at first the fluid, which will find a more ready access to the vesiculae seminales. The semen, as it passes from the testicles, has never been an- OF GENERATION. 495 alyzed; the fluid which has been examined under this name is formed by the semen, the fluid secreted by the mucous membrane of the vesiculae seminales, the prostate, and perhaps the glands of Cowper. At the moment when this fluid passes from the ure- thra it is composed of two substances, the one fluid, and the other thick and nearly opaque. When left to themselves, these sub- stances mix, and the mass liquefies in a few minutes. The odour ' of the semen is strong and peculiar; its taste saltish, and even a little acrid. Professor Vauquelin, who analyzed it, found it com- posed of 900 parts of water, 60 of animal mucilage, 10 of soda, 30 of phosphate of lime. When examined by a microscope, there can be distinguished a multitude of small animalculae, which ap- pear to have a rounded head and a long tail. These singular beings move with a certain degree of rapidity; they appear to avoid the light, and to delight in the shade. To see them, it is only necessary to prick the testicle of an animal at an age when it is capable of fecundation, collect a portion of the fluid dischar- ged, dilute it with warm water, and afterward place it in the focus of a microscope of moderate magnifying power. These animalculae are only found in individuals capable of fecundation; mental depression causes them to disappear. M. Bory-Saint- Vincent sought for them unsuccessfully in two young and vigor- ous individuals who had suffered capital punishment, but found them in soldiers killed in battle; excesses have also been observ- ed to cause their disappearance. They are only found in ani- mals during the rutting season. Mules, though they have, semen, are destitute of them. [The semen is seen to be composed of three distinct elements : a fluid, granules, and animalcules ; the latter are called spermatozoa. The granules of the semen are described by Wagner as round bodies, finely granulated on their surface. They must not be con- founded with the particles of epithelium, which are sometimes mixed with the semen. The spermatozoa were first discovered by a student at Leyden named Horn, and first described by Leewen- hoek. They present different forms in different classes, orders, genera, and species of animals. The figure on the following page is a representation, after Wagner, of the spermatozoa of the human subject and their development.—(Muller.) A. Represents the spermatozoa, consisting of a flattened head and a long, tapering, filiform tail; they are quite transparent. B. Are three granular tubercles, or seminal granules, from which the spermatozoa are developed. C. Are the spermatozoa from the developed granules, lying side by side within the vesicle, which changes from a sphere to a long oval. After a time they break forth, but still adhere to each other for a short period, forming a bundle.] The secretion of the semen commences at the age of puberty; before this period the testicles secrete a viscid, transparent fluid, which has never been analyzed, but which, to judge from appear- ance differs essentially from semen. The revolution which the FUNCTION OF GENERATION. (Fig. 55.) Human Spermatozoa. whole economy undergoes at this period, such as the tone of the voice, the development of hairs, the increase of the muscles and bones, &c, are intimately connected with the existence of the testicles and the secretion of this fluid; indeed, the removal of these organs previous to this period prevents this development from taking place. Eunuchs preserve the same form as in child- hood; their larynx does not increase; their chin is not covered with hair ; and their disposition is generally timid ; and, finally, their physical and moral character very nearly resembles that of females. Nevertheless, many of them take delight in venereal intercourse, and give themselves up with ardour to a connexion which must always be unfruitful. In a state of health, before an emission of semen takes place, the spongy tissue of the penis be- comes warm, hardened, and distended in every direction; in a word, in a state of erection. In this state, everything shows that the blood has been thrown into the penis in large quantity; its arteries are enlarged, and beat with more force; its veins are swelled, and its temperature sensibly augmented. These differ- ent phenomena are evidently under the influence of the nervous system. Different explanations have been given of erection. It has been referred to the compression of the pubic veins by the mus- cles of the penis, and to the constriction of the veins by nervous influence, &c. But, as erection is an action purely vital, can it be explained ? It may be produced by many and very different causes, such as mechanical excitement, venereal desires, the ful- ness of the vesiculae seminales, the use of certain aliments, some medicines, and even certain poisons. It is also excited by several diseases, flagellation, &c. But, of all these causes, the imagina- tion is by far the most prompt. One of the most remarkable phe- OF GENERATION. 497 nomena which attend erection is undoubtedly the great rapidity with which it is reproduced or ceases in certain cases. Gener- ally, erection is attended with oozing of a viscid, transparent fluid, said to come from the prostate. The circumstances which lead to the excretion of the semen, and the sensation which accompanies it, are sufficiently well known; but the mechanism of its evacuation is much less under- stood. Are the vesiculae seminales emptied entirely, or in part, at the moment of emission ? Is it their middle tunic which con- tracts itself, or are they all compressed by other forces ? Do the muscular fasciculi which pass from the orifice of the ureters to the crest of the urethra concur in it ?* Are the levatores ani re- laxed at this instant? Is it the contact of the semen with the membranous or spongy parts which excites the sensation which accompanies its expulsion ? &c, &c. We cannot give any posi- tive answers to these questions. Female Organs of Generation. They are, the ovaria, fallopian tubes, uterus, and vagina; at least, these are the essential organs. From the time of Stenon, the term ovaria has been applied to two small- bodies, situated in the cavity of the pelvis, on each side of the uterus. Each ovarium is formed by an external fibrous membrane, and the interior by a peculiar cellular tissue; in the midst of which are fifteen or twenty vesicles, of which some are larger than others, and correspond, by one of their sides, to the external membrane, which is thinner in that part. These ves- icles appear to contain the rudiments of the germ, and to bear the same relation to women that the eggs do to birds, reptiles, and fishes. They are formed by two membranous envelopes, and by a fluid which runs into a mass, and becomes hardened like albu- men. When the ovaria are not developed, as sometimes happens in some individuals, it exerts an influence upon the economy anal- ogous to emasculation upon the male. Steril women, for this reason, have sometimes a form resembling men; with hair upon the chin and about the mouth, and with a disposition and character like that of men. In such persons, the voice is often grave and so- norous, and the clitoris larger than natural. In this kind of imper- fect woman (called a Virago) is often found inclinations in them- selves immoral, and which are generally peculiar to man, which are interesting in a physiological point of view. The fallopian tubes are two narrow canals, the one on the right, and the other on the left side of the uterus, which are media of communication between the internal part of the uterus and ovaria. Their external extremity is uneven and ragged; they are narrow through the whole of their extent. Their tissue, especially towards the uterus, is very analogous to the vas deferens. In the cavity of the pelvis, between the bladder and rectum, is * See Sir Charles BelL R R R 498 FUNCTIONS OF GENERATION. found the uterus; it is pyriform, and small in the ordinary state, but undergoes a surprising enlargement during pregnancy. We may divide it into body and neck; the last is embraced by the va- gina ; it has three orifices, two at the fundus of the uterus, com- municating with the fallopian tubes, and one below, with the va- gina. The tissue of the' uterus is peculiar; there is nothing analo- gous to it in the animal economy, except some slight resemblance in the heart. Its structure is more easily studied in an advanced state of pregnancy than in the ordinary condition. There are two prolongations of this tissue sent to the inguinal rings, under the name of round ligaments, which spread themselves at the sides of the labia. A great part of the external surface of the uterus is covered by the peritoneum, which forms many remarkable folds about the organ. The internal surface is covered by a mucous membrane; when we examine this surface with a magnifying glass of considerable power, we can perceive a multitude of small open- ings : of which some, less numerous, but larger, belong to the veins of the organ; and others, more numerous, appear to belong to the capillary arteries. The arteries of the uterus are flexuous and large, in proportion to its volume ; the veins are likewise numerous and large. They form in the substance of the tissue what has been improperly called by anatomists uterine sinuses; the nerves are less numerous, and come from the hypogastric plexus. The cavity of the uterus communicates externally with the va- gina, a membranous canal placed nearly vertically in the cavity of the pelvis. It is from six to seven inches long, and its size va- rious, depending upon the circumstance of the individual having had children. Its internal surface, especially at the lower part, has numerous transverse folds, which allow the vagina to become stretched in pregnancy. At the inferior part of the vagina is the hymen, a delicate membrane, which nearly closes up the tube. The tissue of the vagina is composed of grayish fibres, crossing each other in various directions, somewhat analogous to those of the uterus. Below it is surrounded by numerous veins, which re- semble the tissue of the cavernous bodies of the penis, and which form a retiform plexus. It is supposed that this part of the vagi- na is susceptible of erection. All the internal surface of this or- gan is covered with a membrane containing many mucous and se- baceous follicles. The external female organs are the labia and nymphes, folds in the skin, which are destined to become effaced during parturition, and the clitoris, which is a kind of small, imperforate penis, com- posed of two cavernous bodies, and of a sort of glans, covered with a prepuce. It is endued with great sensibility, and undergoes an erection similar to that of the penis. Of Menstruation. In most women, an aptitude for generation is indicated by a pe- riodical sanguineous discharge, which takes place from the inter- nal surface of the uterus, and is a true sanguineous exhalation. It OF GENERATION. 499 is called menstruation, because it returns regularly at the end of a month. There are, however, some women in whom this dis- charge recurs at the end of every fifteen days, others once in two months, others, again, in whom it has no fixed period, and some few cases in which it never appears. The approach of this dis- charge is indicated by particular signs, such as a sense of weight in the loins, lassitude in the limbs, and pricking and pain in the nipples. Its first appearance is sometimes marked by serious ac- cidents ; at others, the discharge suddenly takes place, without any previous indication. , The duration of the discharge, its mode, the quantity of blood exhaled, its colour and consistence, are equally variable. With some women the quantity of menstrual blood is considerable; sometimes to the extent of several pounds. When menstruation continues for eight or ten days, the discharge acquires all the qualities of arterial blood. In some individuals only a few drops of blood are discharged, which is frequently watery and destitute of fibrine ; in others it has all the characters of venous blood ; the evacuation continues hardly a day, or stops and returns again. During menstruation, the susceptibility of females is much in- creased; the least noise frightens, a slight contradiction affects them, and they are particularly irascible. The regularity or irregularity of the return of the courses, the nature and quantity of the blood evacuated, and the duration of the evacuation, are intimately connected with the health of the ndividual; all deserve the particular attention of the physician S has been shown, by the dissection of women who have died during menstruation, that the blood escaped from the mternd«ur- face of the uterus, the vessels of which were found red, and filled with blood, which readily ran into the cavity by slight pressure Although the menstrual discharge takes place from the uterus, yet fhis is lot always the case; many instances have been known wliere this evacuation occurred in the »^™g^t°^ large intestines, stomach, lungs, and even the eye »*^V**m of the skin have also been known to discharge blood periodically, thus it has been known to issue monthly from one or more of the fingers, the cheek, the skin of the abdomen, &c Some distinguished authors, in their anxiety to find the imme- diate^ause of menstruation, have attributed it to the influence of fhf moon to Ae vertical position of the body, and to a generous Set The period at which menstruation first takes place in his rUmate iftoCrds the thirteenth or fourteenth year; it is earlier climate is lo™arufc climates. In equatorial regions, girls !• 1 marked by the development of alarming diseases But it lim Lei recently ascertained, from statistical facts by M. Benois, that this period oi life, so far from being fatal to them, as was long 500 FUNCTION OF GENERATION. supposed, is more fatal to males. What we have said of menstru- ation is liable to many exceptions. Young girls have been often known to conceive before menstruation has taken place; old women, in whom the courses had ceased at the ordinary Period, have had them reappear at the age of sixty or seventy, and have become mothers ; lastly, women in whom menstruation has never Deen observed, have nevertheless become impregnated. Copulation and Fecundation. We have already remarked, that our individual existence is pro- tected by certain instinctive sentiments. A sentiment of the same nature, but much more vivid and imperious, because its end is more important, secures the preservation of the species by inducing the sexes to approach each other for the purpose of coition. The part performed by man in the act of reproduction consists in de- positing in the vagina, as near as possible to the os uteri, the se- men. The part performed by the female is more obscure; a great number perceive, at this moment, the most vivid sensation of pleasure, while others appear insensible, and some even experi- ence pain and disgust. Some discharge a large quantity of mu- cus at the instant when the pleasure is most exquisite, while in the greater number of females nothing of the kind is observed. In all these respects, there are not, perhaps, any two who resemble each other. These different phenomena take place in common copulations, i. e., those which are not followed by fecundation. We will now inquire what takes place in fecundation. We shall pass over in silence the ancient and modern systems of gen- eration. Why should we overload the mind with these brilliant dreams, which have so seriously retarded the progress of science ? According to the latest physiologists, the uterus absorbs the semen, and directs it to the ovaria, through the fallopian tubes, the ragged extremities of which embrace closely this organ. The contact of the semen causes the rupture of one of these vesicles, and the fluid which passes out, or the vesicle itself, is carried into the uterus, where the embryo becomes developed. However satisfactory this explanation may appear, we must take care how we too readily admit it; for it is purely hypothetical, and contrary even to the experiments of the most careful observers. In the numer- ous experiments made upon animals by Harvey, De Graaf, Va- lisnieri, &c, the semen could never be detected in the cavity of the uterus, much less in the fallopian tubes and ovaria. It is the same with the motion by which the fallopian tubes embrace the ovaria; it has never been shown by experiment If we admit that the semen penetrates into the uterus at the moment of coition, which is not impossible, though it has never been observed, it will be then difficult to comprehend how the fluid can pass through the fallopian tubes to the ovaria. The uterus, when empty, is not contractile ; the uterine orifices of the tubes are extremely small, and have no sensible motion. From the difficulty of conceiving how the semen could be trans- OF GENERATION. 501 ported to the ovaria, some authors have imagined that it was not this substance that was carried to the ovaria, but only the vapour exhaled from it, which they called the aura seminalis. Others have thought that the semen was absorbed from the vagina, passed into the venous system, and arrived at the ovaria by the arteries.* The phenomena which accompany fecundation in women, then, are but little understood; an equal obscurity rests on the fecun- dation of the females of other mammiferous animals. With them, however, it will be much easier to conceive of the passage of the semen to the ovaria, inasmuch as the uterus and fallopian tubes are capable of a peristaltic motion similar to that of the intestines. Fecundation in fishes, reptiles, and birds, is effected by contact of the semen with the ovum; it may be presumed that nature em- ploys the same mode with the mammalia. We may consider it, therefore, as highly probable, that the semen passes, either at the moment of coition, or some time afterward, to the ovarium, where it performs its specific action upon the vesicle, which is afterward to be developed. But even if it be acknowledged that the semen finds its way to the vesicle of the ovarium, it still remains to be shown how its contact animates the germ. Now this is a phenomenon of which it is impossible that our senses should take cognizance. It is one of those mysteries which at present are, and will probably always re- main, inexplicable.! But we have the experiments of Spallanzani on this subject, which have done as much towards removing the difficulty as perhaps can ever be effected. This illustrious natu- ralist has proved, by a great number of experiments, first that three grains of semen dissolved in two pounds of water still pre- served its fecundating power; second, that spermatic animalculae are not necessary to fecundation, as several authors, particularly Buffon, supposed; third, that the seminal vapour has no fecun- dating property; fourth, that a bitch may be fecundated by in- jecting semen into the vagina with a syringe, &c, &c. According to the experiments of Messrs. Prevost and Dumas, it would appear that the animalculae are indispensable to fecunda- tion ; that they rise to the upper part of the uterus, but do not enter the fallopian tubes; that a very small grain or corpuscle, contained in the vesicle of the ovarium, passes out at the moment it is torn, that is, some days after coition; that this grain, descri- bed by De Graaf, descends through the fallopian tube, and meets the animalculae, which fecundate it many days after the approach of the sexes. This corpuscle or grain, the existence of which is far from being demonstrated, has been the object of some curi- ous researches by Dr. De Baer. We must consider as conjectural what is said by authors of the general signs of fecundation. At the moment of conception, * If there was any truth in this idea, a female might be fecundated by injecting the semen into the veins. This would be a curious experiment to try. + The same obscurity surrounds this, as we find in the physical and moral resemblance observed between parents and children, the transmission of diseases, the sex of the new in- dividual, &c. 502 FUNCTION OF GENERATION. it is said that the woman experiences a universal thrilling sensa- tion, accompanied with a feeling of extreme pleasure, which con- tinues for some time. The countenance becomes altered; the eyes lose their brilliancy; the pupil is dilated, and the face pale, &c. Without doubt, fecundation is often accompanied by these signs; but how many mothers are there who have never experi- enced them, and who have arrived at the third month of preg- nancy without suspecting their situation ? Our ideas of the chan- ges which take place in the ovaria after fecundation are more ex- act. The most accurate observers have described a body of a yellowish colour, which is developed in the ovaria of fecundated females, which is at first rather large, but diminishes in size as pregnancy advances. But this phenomenon belongs to the his- tory of gestation, which we are now about to investigate. Of Pregnancy, or Gestation. The period which elapses between fecundation and parturition is called pregnancy, or gestation; it is generally nine months, or two hundred and seventy days. All this time is required for the evolution of the organs of the new individual. To form precise notions of pregnancy, it is necessary to study successively the phenomena which take place in the ovaria after fecundation; those of the fallopian tubes, of the uterus and adjacent parts, those of the economy generally, and, finally, those which are peculiar to the foetus. Notwithstanding the numerous observations of anatomists and physiologists on the changes which take place in the ovaria after fecundation, we have still much to learn on this subject. The difficulty consists in knowing what is detached from the ovarium to pass into the uterus. Some assert that they have seen a small vesicle detached from the ovarium, and pass into the fallopian tube; while others maintain that nothing of the kind has ever been observed; but they allege that, a little after fecundation, one of the vesicles of the ovaria is ruptured, and that, with the liquid, there escapes a very small globular body, only visible with the microscope. This molecule, they say, will be the ovum of the ovum ; or, in the figurative language so fashionable in Germany, the ovum elevated to the second power. I shall now proceed to give some of the results of my own observations on dogs, sheep, and rabbits, as connected with this difficult subject. It is difficult to determine in these researches, whether the sub- ject of the experiment has become fecundated. Nothing can be more uncertain than this; we may know, perhaps, that on such a day and hour the female suffered the approaches of the male; but it may have received them before or since; it is impossible always to watch oyer these details. The animals most suitable for these investigations are undoubt- edly the mare and the cow, the vesicles of which are almost as large as hens' eggs. But to make experiments upon these ani- mals would require the resources of a rich agriculturist; and OF GENERATION. 503 even then all the great obstacles would not be removed. There would be still necessary an expertness, disinterestedness, and per- severance not often found in the scientific labours of the present day. Twenty-four or thirty hours after a productive coition, those vesicles of the ovarium which are the most developed augment sensibly in volume. The tissue of the ovarium which surrounds them becomes more consistent, and changed to a grayish-yellow colour. In this state the tissue of the ovarium takes the name of corpus luteum, yellow body. The vesicle continues to grow lar- ger until the second, third, or fourth day, and the corpus luteum grows in the same proportion; it contains a whitish opaque fluid, similar to milk in appearance. After this the vesicle ruptures the external tunic of the ovarium, and passes to its surface, where it adheres by one of its sides. I have seen, in bitches, vesicles thus pass out from the ovarium which had attained the volume of an ordinary hazelnut. In this state, they present no appearance internally that can be considered a germ ; their surface is smooth, and the fluid they contain does not run into a mass as before fecundation. After the escape of the ovum, the corpus luteum remains in the ovarium ; it presents in its centre a cavity, which is large in pro- portion as it is near the period of conception; but in time it be- comes diminished like the corpus luteum itself. This diminution, however, is very slow; and the ovaria always contain those of the preceding generation, which has frequently deceived observ- ers. Thus, the first effects of fecundation take place in the ova- ria, and consist in the development of one or more vesicles, and as many corpora lutea. Sometimes the vesicles are found filled with blood; they appear to have been too strongly affected by the semen. It appears, also, that, in certain cases, the vesicle of one or more of the corpora lutea become ruptured before their entire development; for it is not rare to find more corpora lutea in the ovarium than vesicles at its surface. Action of the Fallopian Tubes. Among the vesicles on the surface of the ovarium, there is ordi- narily one which adheres to the open and mucous mouth of one of these tubes, the tissue of which is softened and gorged with blood, and exhibits a peristaltic motion. I have never directly detected the vesicle in the tube ; but I have often seen the vesicle after it has descended towards the inferior part of the horn of the uterus, while another had contracted adhesions with the extrem- ity of the tube. At this moment, the body of the tube was enlar- ged to nearly half an inch in diameter; it, of consequence, was sufficiently large to allow the vesicle to pass. The period at which the vesicle traverses the tube appears to vary in different kinds of animals. In hares, it appears to take place on the third or fourth day; in dogs, the sixth or eight. It is probable that it is still later in women, and that it does not 504 FUNCTION OF GENERATION. take place until the eighth or tenth. Dr. Maygrier assured me that he had seen the product of fecundation thrown off by an abortion of the twelfth day ; it was a small vesicle, slightly shaggy on its surface, and filled with a transparent fluid. The vascular appendices, in which the tubes terminate in the human subject, are probably intended to contract adhesions with the vesicle, after it is detached from the ovarium, and to pour upon it a fluid that favours its development. After the vesicle had passed, the tube contracts, and resumes its ordinary size. Having arrived at the uterus, the ovum unites itself intimately with the internal surface of this organ; it there receives the materials necessary to its growth, and acquires a considerable volume. The uterus accom- modates itself to this change of form and volume, &c. Alteration of the Uterus in Gestation. During the first three months of pregnancy, the development of the uterus is inconsiderable, and is made in the cavity of the pelvis ; but in the fourth it increases more rapidly, becoming too large to be contained in the pelvis, and rises into the hypogastric region. The organ continues to increase during the fifth, sixths seventh, and eighth months; it occupies gradually a large space in the abdomen, compressing and displacing the neighbouring or- gans, crowding them into the hypochondriac and iliac regions. At the end of the eighth month it fills itself, the hypogastric and umbilical regions, and its fundus approaches the epigastric. After this the fundus sinks, and approaches the umbilicus. The neck of the uterus undergoes but little change in the first seven months of gestation ; the viscus preserves during this time a conoid form. After this the length of the neck is diminished, and at last be- comes nearly effaced, and the uterus assumes an ovoid form ; its volume, according to Haller, is nearly twelve times larger than when empty. It is impossible that the uterus should become altered so re- markably in its form, volume, and situation, without its relations to the neighbouring parts being essentially altered. In fact, the peritoneal coat, which forms the broad ligaments, is stretch- ed, and the vagina elongated. The ovaria, retained by their ar- teries and veins, cannot rise with the fundus of the uterus; they are therefore applied to its side, together with the fallopian tubes. The round ligaments suffer its elevation as far as their length will permit; afterward they offer some resistance to it, which tends to carry the fundus of the uterus forward, which must have a favour- able effect on the abdominal circulation, by diminishing the pres- sure on the large vessels. The abdominal walls undergo a con- siderable extension; hence the rugous appearance upon the abdo- men of women who have borne children. In proportion as the uterus develops itself, its tissue loses its consistence; it assumes a deep-red colour and a spongy texture; its structure becomes more distinctly fibrous. We see, external- ly, longitudinal fibres passing from the fundus towards the neck, OF GENERATION. 505 which are intersected at right angles by circular fibres. Beneath this tunic, the tissue of the uterus presents an inexplicable inter- lacement'of fibres, in which no regular arrangement can be dis- covered. In this state, the organ appears to be endowed with a peculiar contractility, which, in animals, has a great analogy with the peristaltic motion of the intestines. [But one of the most curious phenomena presented by the ute- rus occurs in its cavity after fecundation. As soon as the semen has produced upon the ovarium the important transformation of fecundation of the vesicle, the internal surface of the uterus be- comes the seat of a secretion peculiar to that organ, and which appears to be indispensable to the ovum in the normal state. A coagulable fluid, analogous to the albumen, is deposited, which forms a close sack, lining the inner surface of the walls of the uterus, and extending into the fallopian tubes. At first it is a viscid mass; afterward, by a sort of spontaneous organization, analogous to that of the lymph, it separates into two parts, the one solid, cellular, spongy, which adheres to the uterus, and the other liquid, which occupies the centre of a kind of sack formed by the solid part; it is called the decidua vera. Below is a diagram of a section of the uterus with the decidua vera about eight days after impregnation, from Wagner. A. The neck of the uterus. B B. The entrances to the two fallopian tubes. C. The fringe-like appearance covering the internal surface of the uterus and the entrances of the fallopian tubes, B B, but open at A, the neck of the uterus, is the decidua vera. D Is the cavity of the uterus. This coat, which was first observed by William Hunter, and was called by him the membrana caducea, or decidua, remains during the whole process of gestation. M. Breschet gave to this the name of perione, and M. Velpeau anhiste; the first referring to its situation; the second, its structure. Of the two faces of this false membrane, the one adheres to the inner surface of the ute- rus • the inner surface, according to M. Velpeau, consists of a fine pellicle. The central liquid has never been analyzed ; according to M Velpeau, it is often reddish, and similar to the white of an S s s 506 FUNCTION OF GENERATION. egg. According to M. Breschet, it is at first limpid, colourless, mucous, or slightly albuminous. This liquid at first is in small quantities, but increases with the development of the uterus, until it attains to several ounces. But as soon as the ovum acquires a certain development, its quantity diminishes gradually, and at last, when the ovum has become developed to a certain extent, it alto- gether disappears. There is nothing yet known with certainty respecting the organization of this intra-uterine false membrane. M. Breschet regards it as endowed with organization and life, but adduces no satisfactory proof. M. Velpeau considers it a mere inorganic ex- halation. We shall examine hereafter the curious office that this uterine production exercises on the first descent of the ovum into the uterus. Before this epoch, its use appears to be to close the orifices of the uterine cavity, and particularly to prevent the dis- charge of the liquid gradually deposited in the cavity of this new membrane. This central liquid appears to concur in the slow but regular dilatation of the cavity of the uterus, so as to prepare for the ovum a suitable place of deposite in the uterine cavity, and probably to furnish the first nutritive elements. The changes which take place in the volume and structure of the uterus during gestation require modifications in the circula- tion. In fact, the arteries undergo a very considerable dilata- tion ; the veins also become much enlarged, and form in the pa- renchyma what are very improperly called uterine sinuses; the lymphatic vessels also become very large. It is evident that the quantity of blood that traverses the uterus in a given time is pro- portioned to the changes it undergoes, and the new functions it is called upon to fulfil. A diagram of the ovum after its entrance into the uterus, from Wagner. F. Is the ovum, surrounded with its chorion, G. It has just en- tered the uterus through the fallopian tube, B, pushing the decidua OF GENERATION. 507 vera, E E, before it, to form the decidua reflexa, the name given to that portion of the membrana decidua which surrounds, and becomes, as it were, a part of the ovum after its entrance into the uterus. A. The cervix uteri, or neck of the uterus. B B. The fallopian tubes. C. Points to the decidua vera. D. The cavity of the uterus.] General Phenomena of Pregnancy. While all these phenomena occur in the uterus, important mod- ifications take place in the functions of the mother, and commence often immediately after fecundation. Menstruation does not re- appear ; the mammae swell, and, if in a state of lactation, the milk becomes serous, and is frequently injurious to the infant. The eyelids are swelled, and of a bluish colour, and the countenance altered; the cutaneous transpiration assumes a peculiar odour; a general paleness, with a diminished or capricious appetite, are also often observed ; sometimes continual nausea, with violent pain of the head, followed by distressing vomiting, occurs. The abdo- men is often affected with an extreme sensibility, and at first be- comes flattened; some females lose their sleep, and yet are una- ble to leave a recumbent posture without experiencing a sense of extreme fatigue; on the other hand, persons of a delicate consti- tution, and valetudinarians, often have their health very much im- proved ; alarming diseases are sometimes arrested in the midst of their course, and do not again resume it until after parturition. In general, the intellectual faculties of pregnant females are weakened, and they are affected to an unusual degree by the most trifling events ; hence the necessity of those kindnesses and attentions which this peculiar situation demands. To these dif- ferent symptoms, which it is impossible to explain, are added phe- nomena evidently arising from an augmentation of volume in the uterus, such as cramps in the limbs, swelling of the superficial veins of the thighs and legs, and a sensation of numbness or prick- ing, arising from an obstruction in the circulation. In the later period of pregnancy, the bladder and rectum being strongly com- pressed, the desire of passing urine and going to stool are frequent. We shall not add to these phenomena, the existence of which is certain, suppositions destitute of proof; for example, that fractures in pregnant women are attended with more difficulty than in other women, the contrary of which is shown by experience. Arrival of the Ovum in the Uterus. Tin speaking of the action of the fallopian tube, we have said that there is nothing positively known as to the moment when the vesicle of the ovarium traverses this duct, nor the mode of progression; whether by a peristaltic contraction of the tube, the pressure of the abdominal walls, or by successive adhesions. The little ovoid body, however, arrives at the extremity of the 508 FUNCTION OF GENERATION. tube, where it meets the membrana decidua. But instead of be- coming entangled in its cavity, as was believed by William Hunt- er, and since his time by many physiologists, the ovum glides between the decidua and the uterus, depressing the membrane slightly, or, according to M. Breschet, lodging in its substance. The point at which it stops is variable, but the reason unknown; sometimes it stops in the vicinity of the tubal orifice; at others, descends to the lower part of the uterine cavity, even to its neck. It is easy to comprehend the utility of the decidua during the pe- riod of gestation. It supports the soft structure of the ovum, gently supporting it against the walls of the uterus, with which it forms a close adhesion. The membrane which surrounds or covers the ovum immedi- ately, called the decidua reflexa, in its structure resembles the decidua vera, though thinner. It becomes smooth on its outer surface, which is turned towards the decidua vera, and, like the inner aspect of the latter, is furnished with slight depressions. Towards the ovum the decidua reflexa is rough, and shaggy where it comes in contact with the outer surface of the chorion, with which it unites so intimately, that by the third they cannot be separated. At one part the ovum is not covered either by the decidua vera or reflexa, viz., the part where the placenta is form- ed. This indicates the point at which the reflexion takes place. In extra-uterine conceptions, the decidua vera is formed; but, as the ovum never enters the uterus, there is no decidua reflexa.] Development of the Ovum in the Uterus. At first the ovum is loose in the uterus ; its volume is nearly as small as when it left the ovarium; but, in the course of the sec- ond month, its dimensions increase, and it is covered by long fila- ments of about a- line in length, which ramify in the manner of sanguineous vessels, running into the membrana decidua. In the third month, we perceive them only on one side of the ovum, i those on the other having nearly disappeared; but those which remain have acquired an increased size and consistence, and are implanted more deeply in the uterine wall. In the remainder of its surface the ovum presents only a soft, fleecy coat. The little ovum, when at first it descends from the ovarium, only displaces a very limited portion of the decidua. But, as its volume increases, it detaches and pushes back from the uterine wall a greater extent of the membrane, which then covers one of its faces. The part thus detached projects into the central cav- ity, occupied, as we have seen, by a liquid, and this prominence is enlarged, and the cavity contracted, as the ovum increases. Thus a period at last arrives, about the third month of gestation, when the projecting ovum, covered with the decidua reflexa, meets the concavity of the membrane attached to the uterine walls, the decidua vera. It is unnecessary to add, that from this time, the central liquid of the original decidua vera disappears, in- asmuch as the space that it occupied is now filled with the ovum it- OF GENERATION. 509 self. Former anatomists, particularly Dr. William Hunter, gave to this intra-uterine, membraniform body, the name of decidua reflexa; but they did not understand the true mechanism of its formation. Covering thus the ovum without containing it, the decidua has been compared to a serous membrane, but only as relates to its anatomical arrangement. It does not appear that the two laminae of the decidua vera and reflexa become ever united, as was long believed. At the full period of pregnancy it is still possible to distinguish them, though in intimate contact during the remainder of gestation. The ovum continues to increase and develop itself until the ter- mination of pregnancy, when its volume equals that of the inside of the uterus; but its structure has experienced changes which we are now about to examine. I do not know that any one has observed the human ovum at the moment of its passage through the fallopian tube. In the dog, a little after this instant, it was, as in the ovarium, smooth on the surface. It is not until it has remained for some time in the ute- rus that it becomes covered with asperities. The smallest ova that have been examined in women were eight or ten days old, without the date being positive. They were of the size of a pea, their surface covered with filaments, imparting to them a villous appearance. Beneath this tissue was the ovum itself, formed of a membranous envelope, and interior liquid; we cannot, then,, distinguish any trace of the germ, nor of the different parts, liquid, membranous, or vascular, which ap- pear at a later period. There is not, then, any resemblance be- tween this ovum and that of a bird, where we can easily observe, almost immediately after it has passed from the ovarium, inde- pendently of its membranes, a cicatrix, or first rudiment of the germ, and at least two liquids, which serve for the nutrition of the embryo, the yolk and albumen of the egg. The villosities or flocculi which cover the human ovum have been the object of the special researches of Messrs. Breschet and Raspail. Each of its filaments is simple and fusiform at its point of insertion upon the ovum; it ramifies in such a manner that the trunk is forty times more slender than the summit. The summits of the ramifications form true spongioles, the physical properties of which are very suitable to contract adhesions, and exercise im- bibition. Otherwise these filaments do not offer any anatomical arrangement which could lead one to suspect that they were des- tined, at a later period, to become blood-vessels; for they pre- serve their form and structure to the last period of gestation. Having studied the alterations that the surface of the ovum un- dergoes, let us next examine those which take place in its struc- ture3. About the tenth or fifteenth day, dating from the period of fecundation, and from the fourth to the seventh, from the arrival of the ovum in the uterus, numerous and important modifications "n its structure take place. Instead of one. and the same interior liquid, we begin to distinguish many important parts and organs 510 FUNCTION OF GENERATION. necessary to the development of the ne *r being. ., "■>, t fi oarts are, 1st, the amnios, a thin and flexible m^nbrant ■ first rudiments of the germ, attached to a superficial p<\ a r im- nios, under the form of a small opaque spot; vt r^ ,a ment in their great achievements. It is, however, a rare gift. 528 DREAMS.--INCUBUS. Dreams. When the individual is in health, and the sleep profound, the intellectual functions appear to be suspended, the individual losing for a time his consciousness, the mind slumbering like the body. But this is by no means universal; in some individuals, even in sound sleep, some of the intellectual faculties continue in a high degree of activity; this is especially the case with the imagina- tion and memory. During dreams, the conceptions are some- times striking, and the combinations of thought happy, and seem to surpass the waking powers of the individual. Thus, ingenious contrivances have been made, and the most delightful music com- posed, and individuals of education and taste, who have, perhaps, never written a verse, dream of reading poetry, the beauty and excellence of which their waking thoughts approve. At one mo- ment we recall, with the most graphic accuracy, scenes and ideas long forgotten; in another, we are apparently forgetful of every- thing, even our own identity. Nothing can be more capricious and eccentric than the trains of thought which successively pre- sent themselves in our dreams. The present, the past, and an imaginary future roll before the mind in strange confusion; vis- ions in which truth and error, the most brilliant and sublime con- ceptions combined with thoughts more wild and fantastical than could occur to one sane and awake, incessantly glide before it. It seems to afford a sort of living illustration of the possible inde- pendence of the mind upon the body; the individual appears to see without light, hear without sound, and to be transported with- out motion, by " most miraculous organs." It may be doubted if dreaming ever occurs in a perfectly normal state. There are reasons for considering this phenomenon as always indicative of a morbid condition, though often slight and transient. There is an obvious analogy between dreaming and delirium. In both the mental faculties are perverted, and in both the sensations and sen- ses report falsely. It is certain that the dreams become more wild and impressive, and diminish the salutary effects of sleep as the health becomes more infirm. Excitement of the mind increas- es the disposition to dream, and renders the sleep disturbed and unrefreshing. If mental excitement be carried beyond a certain point, the power of sleep abandons the individual; and his wa- king thoughts at last become " such stuff as dreams are made of." Incubus. During sleep, the power of voluntary motion is, to a certain ex- tent, suspended. In our dreams, we appear to transport ourselves through space with the speed of thought; yet we make not a muscular effort. Though we appear to ourselves to possess the power of voluntary motion as fully as when awake, and seem to talk and walk as usual, yet our volitions do not prompt our mus- cles to action. In the class of dreams called incubus, we are conscious of a loss of this power, and the sensation is most dis- NATURAL SOMNAMBULISM. 529 tressing. The patient experiences a sense of oppression about the praecordia, with embarrassed respiration, a consciousness of imminent danger, to which is superadded some frightful vision. He is incapable of the slightest power of voluntary motion or speech. He thinks, perhaps, that he is falling from a great height, or that he is standing on the verge of a precipice. He thinks, perhaps, that some movement is necessary to save himself from instant death. He struggles to accomplish it, or to cry out for aid; but his muscles refuse obedience to the mandates of the will. There is a temporary, but universal, paralysis of the muscles of animal life. It is remarkable, that while in this state, the slight- est motion, often that of a finger, or a slight external excitement, as the voice of another, is sufficient to break the charm, and in- stantly restore the individual to his usual health. But in some cases, the impressions made by these dreams are such that it re- quires some time for the patient to rouse himself to a full con- sciousness of his situation, though awakened. This variety of dreams, incubus, is one of the most comm«n symptoms in many pathological conditions. In diseases of the heart and large vessels, and other chronic diseases of the chest, in which there is much dyspnoea and watchfulness, as asthma, hydrothorax, empyema, &c, chronic diseases of the liver, and in dyspepsia, especially after eating at night, it is a common and distressing symptom. It may arise from various causes; it is, perhaps, in most cases, more immediately connected with disor- dered functions of the stomach. Somnambulism is another modification of dreams. It differs from common dreaming in this, that the individual retains, more or less perfectly, the power of voluntary motion, and actually ex- ecutes during "sleep what in other dreams is only imagined. Thus, individuals have been known to rise from their beds, go considerable distances, and in dangerous places, and return, yet in the morning be perfectly unconscious of what has happened. While the somnambulist is'walking about, and even though the eyes be open, there is a want of speculation in their expression, and entire abstraction of the patient from surrounding objects and events, as in a common dream. They sometimes perform various acts which appear to imply vision, as walking in safety in perilous situations, writing, &c. Sometimes the eyes are shut, and they are heedless of surrounding objects, as in common sleep. When this state occurs spontaneously, it is called natural som- nambulism. It is also alleged that a state of somnambulism may not only arise spontaneously in natural sleep, but, under certain circum- stances, be artificially induced. The art of producing this state has been called, from its founder, Mesmerism, or animal magnet- ism. It has been alleged that certain gifted individuals, either with or without the magnet, and in consequence of some inherent mysterious power, can, at will, throw certain individuals into a state of somnambulism, and exert over them, while in this state, a X x x 530 ARTIFICIAL SOMNAMBULISM. charm more potent than midnight witch, " with poppy or man- dragora." That a state of sleep or dreaming called artificial somnambu- lism may be induced in certain persons, appears to rest on strong proofs; but, at the same time, the subject is involved in great ob- scurity and difficulty from the superstitious excitement and self- delusion so common in this class of patients, and from its having been frequently combined with collusions and deliberate impos- ture. The class of persons liable to this pathological condition are chiefly those of vivid imagination, excitable tempers, and delicate health, constituting what has been called persons of a nervous temperament. The patient, after having been subjected to cer- tain ceremonies, begins to yawn, the eyes become heavy, and at last he appears to sink into a profound sleep. The tempera- ture of the body is sometimes increased, and the pulse and respi- ration accelerated; at others it is the reverse, while occasionally no essential change takes place in either of these respects. There is often, during the paroxysm, twitching of the muscles of the face and a highly-excited state of the nervous system. The intellect- ual functions seem to be in a state analogous to that described as natural somnambulism. Though apparently the patient be asleep, and unconscious of everything passing around him, he may hold a continuous and coherent conversation. The memory, in some in- stances, has appeared to be remarkably developed, the person describing past events, quoting largely from books, and speaking in languages acquired in childhood, all of which was said to have been forgotten. Sometimes one or more of the senses have been stated to be suspended or remarkably modified. Thus, the loudest noises, as the report of a pistol, calling loudly, shaking, pinching, and pricking, and dashing cold water in the face, and, as has been recently alleged, even performing formidable surgical operations, have not appeared to excite the slightest emotion or wincing in the patient, yet a small current of air, blown with the mouth upon the skin, or the ticking of a watch, has seemed to annoy him. The sense of smell has in some instances appeared to be suspended, so that the most pungent odours, as strong am- monia, have been snuffed up without causing the slightest incon- venience. The muscular power has been observed in some cases to be remarkably developed. Patients in this state have been known to leap to a great height over the furniture, upon the windows, &c, and to balance themselves in difficult postures. The patient may remain in a state of somnambulism for a longer or shorter time, after which he will awaken. It often appears difficult to rouse the patient from this state, as in ordinary sleep, by calling, sha- king, &c.; yet, by flirting the hands for a few times before the face, or, as the magnetizers express it, by " renewing the passes," the paroxysm will pass off, the patient appearing like a person awaking from a deep sleep, and perfectly unconscious of all that ARTIFICIAL SOMNAMBULISM. 531 has passed. In some instances, patients have remained in a state of lethargy for hours; and in others, catalepsy, epilepsy, and con- vulsions have supervened. From what has been said, it will be perceived that there is much connected with this condition fitted to excite superstitious wonder, and offer ample scope for the ig- norant and designing. Hence the many marvellous tales, and incredible, indeed impossible, things alleged respecting this class of patients; such as speaking languages they had never learned; describing accurately remote places and things of which they were ignorant; distinguishing the visual qualities of objects, not only with their eyes closed or covered with triple or quadruple bandages, but when applied to the back of the head. The power of performing these miracles with fantastical precision has been called clairvoyance. When this pathological condition occurs spontaneously in the progress of sleep, it is obviously dependant upon idiosyncrasy. It is, for the most part, connected with some disease, as hysteria, indigestion, mental agitation, &c. Artificial somnambulism is in- duced by certain forms and ceremonies, during which the opera- tor has been alleged to transfer to the patient a peculiar agent, called the magnetic fluid. The ceremonial consists in making what are technically called " passes," i. e., passing the palms of the hands near the head, face, and along the sides of the patient; or by personal contact; pressing the lower extremities of the pa- tient between those of the operator ; placing the hands upon the head, grasping the thumbs &c.; or by merely looking intently or steadily at the patient. It has been even pretended that the mag- netizer may transfer his power to other objects; e. g., M. de Puy- segur asserted that there was a certain tree in his garden, which he had so charged with animal magnetism, that persons, by look- ing at it, were thrown into a state of magnetic ecstasy. Does this explanation, given by professors of animal magnetism, satis- factorily explain the symptoms and causes of artificial somnam- bulism as described ? Have we any evidence of the existence of a fluid possessing these remarkable properties ? Is there sufficient evidence to warrant the belief that any individual possesses the power of transferring by volition such fluid ? or is this state al- together a fiction ? or, admitting its existence, can we satisfacto- rily explain the phenomena of artificial somnambulism by the known laws of the animal economy ? Though this subject has been so often combined with self-de- lusion, trick, and imposture, that it is almost impossible to draw the line between truth and error, and the facts must, more or less, rest upon the statements and actions of the patient, yet the occa- sional occurrence of such a condition rests upon testimony that cannot reasonably be altogether rejected. Admitting this, it would seem that this state is chiefly referrible to the influence of the imagination over the functions of the brain and nervous sys- tem, and, through them, the physical condition of the other or^ans. We can scarcely fix a limit to the effects of the imagination. 582 ARTIFICIAL SOMNAMBULISM. Every intelligent phvsician is aware of its powerful influence, both in the production and cure of diseases. Thus, in fatal epidemics, we often see individuals protected frOm their effects, or rescued from the most perilous condition by their confidence in some unim- portant medicine, or some rite, amulet, or charm, the whole efficacy of which depends upon the excited imagination of the patient. We see epilepsy, catalepsy, hysteria, chorea, and other diseases simulated during somnambulism, and even sudden death, caused by mere mental emotion, hope, fear, anger, &c. The student of medicine can at first scarcely read a graphic description of a dis- ease without experiencing in imagination all the symptoms. The force of imitation, in causing diseases, is also notorious, and is especially operative in childhood, and in persons of a nervous temperament. This sympathetic tendency is shown in inducing coughing, gaping, hiccoughing, vomiting, and other spasmodic af- fections. Whole schools have been seized with convulsive dis- eases from witnessing the terrific grimaces and contortions of an epileptic. We often witness this strong instinctive tendency to imitation in the repetition of atrocious crimes which have ex- cited great horror. Thus, in Paris, at one of the large hospitals, a patient committed suicide by hanging himself in a certain door- way. The same thing was several times repeated in the same place, until the governor of the hospital ordered the door to be closed up with masonry, and the crime was no longer perpetrated. On the other hand, there is no doubt that many of the surprising cures attributed to the tombs and prayers of saints and holy rel- iques, and amulets, and magical charms, were actually performed chiefly through the agency of the imagination. The same remark applies to Thomsonianism, homoeopathy, and empiricism in every form. The question in many of these cases is not so much as to the facts of the cure as their mode of production or causes. From what has been said of somnambulism, it would appear that it consists essentially in lesion of function of the great ner- vous centres. There is a strong affinity between it and other common pathological conditions supposed to depend upon this cause, as lethargy, catalepsy, hysteria, &c, with which, indeed, it is sometimes complicated. When fairly considered, there is nothing more remarkable about this than other analogous patho- logical conditions. Many of the wonderful stories related re- specting it are probably the results of accidental coincidences. self-delusion, or imposture. It is chiefly interesting from the light it throws on the physiology of the nervous system, and the etiol- ogy, pathology, and diagnosis of its diseases. ArtificiaUsomnam- bulism has been occasionally resorted to, therapeutically, to pro- cure sleep, particularly in cases of great nervous excitement, where the use of the narcotic drugs was objectionable. Every well-informed physician must be aware of the great influence which the mind exerts over the physical condition of the organs, both in inducing and removing disease, and in his practice will be duly governed by this knowledge. But he will not forget that OF DEATH. 533 self-respect and the dignity of the profession demand circum- spection on these points. He will remember how readily mystery glides into charlatanry, and how apt the profession is to become degraded even by its semblance, when countenanced by respecta- ble practitioners. Nor is this the only objection to resorting to these ceremonials. In the ecstatic state thus induced, there is certainly danger, particularly in nervous females and other excitable subjects, of causing convulsions, hysteria, epilepsy, &c, and that this practice may be otherwise grossly abused. It is to be regretted that an ultra spirit of refinement has extended its inroads within the dominions of science. It has manifested itself not only in the miracles of animal magnetism, but also, under the specious title of Transcendentalism, men of reputation and ability have ventured to practice a sort of learned trifling most dangerous to the interests of science. In this spirit we are called upon to listen to fair-drawn distinctions and obscure analogies; we are cautioned against limiting the laws of nature and narrowing the boundaries of science; and are warned against disbelieving alleged facts merely because they appear absurd and impossible. It is a subject of congratulation that the members of the profession in this country are little infected by this innovation, but are still inclined to follow the plain dictates of common sense and the spirit of the inductive philosophy in their scientific reason- ings on these subjects.—Ed.~[ OF DEATH. The individual existence of all organized bodies is temporary; no animal escapes the hard necessity of dying; nor is man ex- empt from this. The particular history of each function shows that in the first periods of old age, and often before, the organs become deteriorated; that many completely cease to act; that others are absorbed and disappear; and, lastly, that in decrepi- tude, life is reduced to a few miserable remnants of the vital, and some of the nutritive functions in an imperfect state. In this con- dition, the most trifling external cause, the slightest blow or fall, is sufficient to arrest one of the functions indispensable to life, when death immediately follows, as the last degree in the destruction of the organs and functions. But a small number of persons die solely through the effects of age; it scarcely happens to one in a million; the remainder die at every period of life, by accidents and diseases. This great destruction of human life, by causes apparently accidental, appears to be provided for by nature, with as much care as she takes to secure the reproduction of the spe- cies. THE END. M INDEX. Pag( Admission of Air to Glottis . . . 400 Action of Kidney.....466 Animal Heat, how produced . . . 487 " " Experiment of Despretz . 489 Absorption of Pulmonary Veins . . 418 Allantoides......513 Air in Expansion of Chest . ... 394 " " Experiments on 395 Action of Fallopian Tubes . . . 503 Artificial Respiration .... 410 Achromatism......41 Apparatus of Vision . . . .42 Action of Retina.....63 " " Effects of intense Light 63 Apparatus of Voice . . . .193 Auditory Nerve.....84 Anatomy of Lungs.....390 Apparatus, what.....17 Amnios.......511 Amaurosis......77 Areoles of Organs.....17 Absorption of Veins .... 367 " " Experiments on . 369 Apparatus of Hearing, Diagram of . 79 Action of Auditory Nerve Art of Ventriloquism .... 213 Atrophy of Brain.....165 Apparatus of Tears: Diagram . . 46 Arterial Blood: Fat in . . . .411 Globules of . 412 " " Man . . . .413 « « Frog . . .414 Apparatus of Arterial Blood . " Pulmonary Veins " Left Ventricle . " Arteries . Action of both Ears . . .89 Anastomoses of Uterus and Placenta . 518 Action of both Eyes . . .66 " " Direction of Light . 66 Anatomy of Encephalon . . .140 Attitudes of Man.....225 Apparatus of Smell . . • .93 " " Diagram of .94 Action of Large Intestines . . . 309 " " Accumulation in 310 Action of Small Intestines . . .303 Action of Stomach on Aliments . . 286 Accumulation of Aliments in the Stom- ach .......288 Alteration of Aliments . . . .291 Abdomen : its Divisions .... 285 Aliments and Drinks .... 270 " " Properties of . 271 Apparatus of Touch and Sensation . 108 Difference of 108 Assumptions of Craniology . . .159 Accumulation, Chyme in Small Intes- tines ....... 304 » ' « Changes of . . 305 « " Chemical Analysis of 306 Action of Cerebro-spinal Nerves . 178 Page Attitudes, different Ages . . .249 " Sensations, Attitudes, and Motions 250 Attitudes, Motions, and Will . . .252 " " remarkable Case of 253 Attitudes, Motions, and Instincts . . 254 Acts of Digestion.....272 Atmosphere: its Mechanical Properties 397 " " its Chemical Properties . 398 Attitudes and Movements . . . 219 " Mechanical Principles involved 220 " Levers.....220 Absorption and Course of Chyle and Lymph......329 Absorption of Lymph .... 340 " " Lymph .... 339 Base of Cranium.....31 " " in Man and Orang-ou- tang . .....32 Beaumont on Digestion .... 297 Bones: their Action in Attitudes and Movements.....223 Beaded Filaments of Muscles . . 184 Brain in Motions.....242 " Hemispheres .... 243 " Corpora Striata .... 243 " Cerebellum.....244 Bones of Ear: Diagram of . .81 Brain of Man and Animals . . . 144 Base of Encephalon .... 139 Biology.......7 Blood necessary to Action of Organs . 433 " Influence of Nervous System on . 433 Blood in Aorta.....419 Bile: its Secretion .... 459 " Analysis of.....461 Cerebro-spinal Nerves: Experiments on, by Mr. Mayo.....175 Changes of Aliment in Stomach . . 294 Chyme accumulates in Pyloric Portion . 292 " its Taste.....292 Changes from Age in Crystalline . . 73 Cerebral Influence in Muscular Contrac- tion .......189 Chyle.......330 " its Absorption .... 333 " Physical Process .... 334 " Intestinal Villi . .335 Course of Chyle.....336 Contents of Stomach .... 262 Cartilages and Muscles of Larynx . 196 Cavities of Brain.....142 Chemical Analysis of Brain . . . 143 Course of Lymph.....352 Course of Venous Blood . . . 354 Crystalline Humour : its Uses . . 55 " Effect of Removal 55 Capacity of Pulmonary Artef^ in Trunk and Branches.....387 536 INDEX. Page Convolutions of Brain: Number and Depths of Furrows . . .160 Case of Dr. Boerstler . . . .161 Contraction of Arteries not Muscular . 388 Course of Venous Blood . . . 364 Cartilage of Ear.....80 Caruncula Lachrymalis . . . .45 Choroid Coat: Uses . . . -62 Conjunctiva: its Structure . . .47 Cataract.......75 Ciliary Processes: Uses . . .6: Case of James Mitchel .... 124 Case of Laura Bridgman . . . 125 Ciliary Nerves: their Division . . 60 Contractility : Organic, Sensible, Cere- bral, Voluntary.....23 " " their Nature . 24 Circulation of Blood: Quantity of; Ef- fect on Size of Organs . . 429 " " its Analysis in Vessels 431 Curvatures of Arteries .... 420 Contraction of Arteries .... 421 Connexion of Arteries and Veins . . 422 Course of Arterial Blood . .416 Conversion of Venous into Arterial Blood 404 Characteristics of Man: Erect Attitude 27 " Bimanous and Biped . . 28 " Muscular Strength of Inferior Extremities..... Circulation of Fcetus .... 516 Classification of Functions . . .35 Cutaneous Transpiration . . . 452 Chemical Properties of Organs . . 18 Connexion of Pulmonary Artery and Veins.......391 Deglutition......280 " Mechanism of 281 " Phenomena of . . . 284 Diagram of Globe.....52 Dreams.......528 " Incubus.....528 " Somnambulism .... 529 " " Natural . . 530 " " Artificial . . 531 Death.......533 Digestion......257 Digestion and Functions of Relation . 327 " Great Sympathetic in Digestion 329 Drinks: Digestion; Prehension . .315 " Deglutition; Accumulation . 316 " Alteration in Stomach . . 317 '• Action of Small Intestines . 319 Differences between Dead and Living Bodies ... . . 14 " between Animals and Vegetables 15 Division of Substances .... 7 Digestion in Man and Animals . . 261 Desire or Will.....151 Difference among Men in Intellect . 152 Digestion, Fcetus.....519 " " Nutrition of . . 520 Deglutition of Air ..... 320 Dilatation of Lungs . . . .396 Dermis.......110 Eighth Pair of Nerves in Digestion Experiments of Montegre Eyelids: their Structure; Muscles tilages .... " Cellulftr Tissue " Action; Follicles Car- 302 296 43 43 44 Eye compared to Camera Obscura Eustachian Tube . Expulsion of Faces . • Endosmosis and Exosmosis . Effect of Use on Organs of Sense . Estimate of Distance of Bodies " of Motion Eye liable to Disease Experiment of Deleau . Epidermis..... Experiments of Flandrin Experiments on Taste . Eyebrows: Uses .... Eructation and Vomiting Experiments on Smell . Experiments, their Importance Eighth Pair of Nerves . Exhalation : Serous, Cellular Tissue " Adipose Experiments of Savart . Exhalation : Synovial; Interior of Eye Cephalo-Rachidian Excretion of Urine .... External Ear..... Experiments on Voice . Encephalon, what .... Eighth Pair of Nerves . . 54 . 87 . 313 . 18 . 106 . 67 . 68 . 76 . 209 . 109 . 337 . 103 . 42 . 321 . 96 . 6 . 417 . 443 . 444 . 78 ! 445 . 468 . 80 . 199 . 136 . 390 Fecundation......500 " Experiments on . . 501 Function of different Parts of Brain . 163 Form of Bones . . . . . 223 Follicles of Lieberkuehn . . . 449 Follicular Secretion .... 454 Facial Angle of Camper . . .30 " in Man and Horse . . 31 Faculties peculiar to Man : Voice; Ca- pacity of Improvement; Sense of Re- ligion .......34 Fluids in Small Intestines . . 264 Fecal Matter, Chemical Analysis of .311 Female Organs of Generation . 497 Functions of the Encephalon . . 135 Functions of Lymphatics . . . 341 " Experiments on Lymphatics . 344 " Experiments on Absorption of Lymphatics.....346 Form of Larynx.....194 Functions of Nerves .... 121 Fluids or Humours . . . .19 Ganglionic Globules . . . .118 General Doctrines of Secretion . . 471 " " Physical Influence 471 " " Chemical " . 473 Generation, Organs of, in Man . . 491 Glandular Secretions .... 455 Glands of Brunner.....450 Globe of the Eye.....49 Glottis in Inspiration .... 400 General Anatomy; its Origin; Bichat and Pinel . . . . . .16 Germ . . . . .514 Hunger.......266 Honore Tresel, Case continued . . 217 Heart, Motions of; Contraction of Auri- cles ; Contact with Chest . . . 424 " First and Second Sounds of . 426 " Pulsation of different Ages; Force of.......426 INDEX. 537 Humours of the Eye " " Coats of the Eye Hearing and the Voice . Hearing..... Human Spermatozoa Human Understanding . Head of Man; Organs placed there Hepatic Vein .... Honore Tresel Page 50 50 216 77 496 146 30 459 89 Insalivation......275 Instinct, its Uses.....154 Internal Sensations . . ■ .113 " " not all Parts . .113 Intellect: distinctive Character of Man 33 Intestinal Mucous Membrane . . 448 Induction, due to Galileo ... 5 Intellect of other Animals . . .34 Images of Objects inverted . . .40 Immediate Principles . . . .19 " " Azotic and Non-azotic 19 Imperfect Vision.....75 Inflections of Muscular Fibre . . 183 Iris........50 " its Structure.....51 Incus.......81 Inspiration and Expiration . . . 399 Page Menstruation......498 Memory.......149 Modification of Smell by Age . . 100 Motions of Iris.....59 Mechanism of Smell . . .95 Modifications of Digestion by Age . . 323 Mechanism of Sensation . . .110 Modification of Taste by Age . . 107 Mechanism of Contraction and Expan- sion of Chest.....392 Mamma.......524 Milk Ducts......525 Middle Ear......80 Muscular Contraction .... 182 Motions and the Voice .... 255 Myopia.......75 Mechanism of Vision . . . .53 Mechanism of Mastication . . . 278 Motions, Partial and Locomotive . . 231 Motions of Eye.....232 of Face.....233 " of Head . .„ . .234 of Trunk.....235 " of Superior Extremities . . 236 " of Inferior " . • 237 Man Zoologically ..... 15 Judgment Joints 150 224 Kidney, Vertical Section of . . . 463 " Portion of in Infant; Corpora Malpighiana; Tubuli Uriniferi . . 464 " Magnified Portion of . . 465 Kneeling.......229 Lamellae of Membranes . . . .18 Lactation......523 Lesions of Medulla Oblongata . . 245 Leaping ....... 239 Lingual Nerve.....104 Lachrymal Ducts.....46 Lachrymal Gland.....45 Labyrinth: Diagram . . . .82 List of Humours.....20 " " their Classification by Prof. Chaussier..... " " their Physical Properties " " their Appearance by Mi- croscope; their Chemical Properties; their Vital Properties .... Lobules of Liver.....459 " " Section of . . . 460 Light: its Nature, according to Des Cartes; to Newton . . . .36 Light consists of different Rays; Solar Spectrum . ... . .41 Structure of Body .... 15 " Predominance of Fluids . . 15 Solids ... .16 Man is Social.....33 Motion of Blood.....434 " " Influence of Inspiration and Expiration on ... . 435 " " Experiments on . . 436 Modification of Hearing by Age . . 91 Muscular Contraction and the Voice . 179 Medulla Spinalis.....169 23 Lesions of Medulla Spinalis Light: its Velocity " Ray of " from Luminous Bodies Membranous Labyrinth . Meatus Auditorius . Muscles of Eye: Diagram of Mechanism of Hearing . Malleus .... Diagram of Modification of Voice by Age Moving Power in Attitudes Mastication Mechanism of Voice Mastoid Cells Muscles in Attitudes Mechanism, Sensations 170 214 221 274 198 87 226 120 256 Nutritive Functions Nervous Plexus.....119 Offices.....119 Nerves: Essential Organs of Sense . 115 " each Filament executes but one Office; Views of Sir C. Bell . .. 116 Notes of the Chest.....210 Nutrition, what.....481 " Influence of Non-azotic Ali- ments . . . . . . 483 " " various Aliments 485 Nasal Fossa?......95 Nerve with Ganglion .... 118 Neuralgia......177 Nerves of Motion.....180 their Structure 181 Of the Passions.....156 Offices of Cerebrum and Cerebellum .157 Opinions of Dr. Gall . . . ' . 158 83-84 " " Bouillaud , .158 Offices of Cerebellum .... 167 53 " " Experiments by Lassaigne 168 85 Organs of Digestion .... 257 81 " " Diagram of . .239 Yyy 538 INDEX. Organs of Digestion, Structure . 260 Origin of Lymph . . .351 Optics, Catoptrics, Dioptrics . .36 Ovum in Utero.....506 " " Development of . . 508 " " Diagram of . 510 Optical Illusions .... 63-68 " " corrected by Experience 70 " " Case of Cheselden . 70 Origin of Compound Nerves . . • 171 Organic Muscular Fibres . . • 185 <« " Contract unequally 186 Optic Nerve . . ... 51 " its Origin; Crossing of . 52 " Experiments on . . 52 Olfactory Nerve.....95 Os Orbiculare.....81 Optic Nerve resembles .... Pylorus: its Action .... 293 Pulsation of Pulmonary Artery . . 387 Pulmonary Artery......363 Puberty on the Voice . . . .215 Presbyopia......75 Pituitary Membrane . . .94 Pupil of Eye of Horse . . . .59 Peyer's Glands.....450 Present State of Physiology . . .25 Prehension of Aliments .... 273 Pathological Tendencies of Hearing . 90 Pregnancy......502 Parotid Gland.....457 Pancreatic Juice.....457 Placenta......515 Parturition......521 Pulmonary Transpiration . . . 405 Passage of Venous Blood through Heart 380 " " through Pulmonary Artery 384 Pelvis of Man: Peculiarities of .29 Physical Properties of Organs . . 17 " " Imbibition . . 17 Physiology: Definition .... 5 " differs from exact Sciences 6 Predominant Character of Man; Intel- lectuality ......30 Quantity of Air in Chest . . . 401 " its Physical and Chemical Changes 402 Righr Cavities of the Heart . . .362 " Foramen Ovale ; Eustachian Valve 362 " Columnar Cornea? .... 369 Respiration, what.....389 Restoration of Voice .... 216 Rigor Mortis......188 Running.......241 Refraction of Light . . . .37 Refracting Media; their Influence on Light.......38 " their Density and Combustibility 38 " when Curved Surfaces . . 39 Retina.......64 " Receives Impressions; Extent of 65 " . Anatomy of .... 65 Relations of Smell to Digestion " " to Encephalon . 99 Refracting Parts of the Eye . .49 Regurgitation.....321 Recovery of Senses : its Effect .133 Recumbent Posture . . .231 Secretion, what Sudoriferous Gland Sensible and Insensible Perspiration Solitary Gland Sitting..... Section of Eighth Pair of Nerves " Sanguineous Solution of Aliment in Stomach Spontaneous Vomiting . Saliva..... Sixth Sense . Secretions derived from Blood " Animists " Inferences from Section of Head Section of Peduncles of Cerebellum " " of Pons Varolii " " of Pyramidalia Sounds independent of the Voice Sensibility .... " its Origin Sense of Smell " "its Production Sensations explained Stapes..... Sounds ..... " how divided " how propagated Sense of Taste " Apparatus " Mechanism . Sapid Bodies .... Singing..... Smell connected with Digestion Structure of Muscles Sigmoid Valves: their Form . " " their Action Sounds of Letters . Savart on the Larynx Society: its Effects Structure of Lungs Superficies of Lungs Sounds of First Register " Second Register Sleep Sneezing Standing on one Foot Spine, in Attitudes Swimming Simple and Compound Substances Simla?: Conformation of Structure of Nerves Secretion of Tears . " of Saliva Sensation and Voluntary Motion Secretion of Tears: their Course Teeth .... Temperature of Food Touch : its Mechanism . " its Perfection " Modified by Age Tissues resemble Sponges Touch . Tympanum Tears: their Uses . Tongue . Transparent Comea Tutamina Cerebri . Transparent Parts of Eye Thorax of Man: Form and Capacity Table of Tissues.....17 INDEX. 539 Transparent Bodies Thirst Transfusion of Blood Agents in Infusion of Medical Introduction of Air 37 269 439 440 441 Use of External Cartilage of Ear Use of Membrana Tympani . Uses of Aqueous Humour . •■ Uses of Internal Ear Uses of Nose .... Uses of Cavity of Tympanum Urinary Bladder Uses of Motions of Iris . Uterus: Alteration in Pregnancy " Diagram of Urine: its Secretion Uses of Comea Page Vertebral Column of Man: its Outline; Object of; compared with Animals . 29 Vital Phenomena reducible to Nutrition and Vital Action . . .26 Vitreous Humour: its Uses . .56 » " Hyaloid Cells . . 55 " •* Experiments . . 57 Voice.......191 85 " compared to Musical Instruments 192 85 Vision at different Ages . . .73 54 Vesicula Umbilicalis .... 512 87 Vision Defined.....37 97 Vision, in Childhood . . . -74 86 " Old Age.....74 467 Vertical Section of Encephalon . . 171 61 Venous Blood: its Character . . 355 504 " " Analysis . . . 356 505 Veins......"359 462 " their Communication with Arteries 360 54 " their Structure . . . .361 Vital Phenomena.....25 " Causes of, according to Ancients 25 Walking 23T N^rvv5 VALUABLE WORKS PUBLISHED BY HARPER & BROTHERS, NEW-YORK. 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