AN ANALYSIS OF PHYSIOLOGY: & Cnttiunsifo IUbio MOST IMPORTANT FACTS AND DOCTRINES. DESIGNED ESPECIALLY FOR THE USE OF STUDENTS. JOHN J. REESE, M.D., LECTURER ON MATERIA MEDICA AND THERAPEUTICS IN THE MEDICAL INSTITUTE OF PHILADELPHIA; PHYSICIAN OF WILLS' HOSPITAL; FELLOW OF THE COLLEGE OF PHYSICIANS. SECOND EDITION, REVISED AND ENLARGED. ■K\ Qr?o PHILADELPHIA: LINDSAY AND BLAKISTON. 1852. QT ~R3&:■; 155 Physiological differences in the Tissues, The Temperaments, Symmetry—Its deviations, PART TV. THE ACTIONS OF THE LIVING ORGANISM. CHAPTER I. organic or life actions. CHAPTER II. OIIGANIC0 CHEMICAL ACTIONS. Molecular Disintegration and Renewal. 157 Section I.—Digestion and Food, .... 159 Classification of Food, . . 159 Varieties in the Digestive Apparatus, . . 163 Action of the Mouth and Oesophagus, . 165 Influence of the Saliva, . . 165 Action of the Stomach, 167 The Gastric Juice—Pepsine, . 168 Action of the Intestinal Tube, 171 Influence of the Bile in Digestion, 172 Hunger and Thirst, .... 173 II.—Calorification or Animal Heat, . .174 III.—Secretion, ..... 179 Difference in the structure of Glands, . 181 Nature of Secretion, . 182 The Liver—Secretion of Bile, 183 Analysis of Bile, . . 184 The Kidney—Secretion of Urine, 186 Analysis of Urine, ... Igg Origin of the Solids of the Urine, . .190 Kreatine, Kreatinine, Inosinic Acid, Sarcosine, Kiesteine, ... in- The Mammary Gland—Secretion of Milk, . 197 Composition of Milk, . 198 The Salivary Glands and Pancreas, 201 The Lachrymal Gland—The Tears, oqI The Testis—Spermatic Fluid, o()„ CONTENTS. XI Cutaneous and Intestinal Secretions, . . 202 Sudoriparous Glands, . . . 203 Sebaceous Glands, .... 204 Glands of Brunner and Peyer, . . 205 The Spleen, ...... 206 Supra-Renal Capsules, .... 207 Thymus and Thyroid Glands, . .207 CHAPTER III. physical actions of the organism. Capillarity and Imbibition, ..... 208 Endosmose and Exosmose, ..... 209 Absorption, ....... 212 Intestinal and Lacteal Absorption, . . 213 Cutaneous and Pulmonary do. . . . .214 Diffusion of Gases, . . . . . 215 Exhalation, ....... 216 Elasticity, . . . . . . 216 Electrical Phenomena, ...... 216 CHAPTER IV. dynamical and mechanical actions of the organism. Source of the Dynamic Forces, ..... 221 Functions influenced by the Dynamic Forces, . . 224 Section I.—Respiration, ..... 226 Different Forms of the Respiratory Apparatus, 229 Dynamical Phenomena of Respiration, . 232 Chemical Effects of Respiration, . . 2-35 Asphyxia, ..... 240 II.—The Circulation of the Blood, . . .242 Circulation in Plants, . . . 243 Movement of Rotation, .... 243 Varieties in the Circulation of Animals, . 244 The Heart, ..... 247 Sounds of the Heart, ... 250 Action of the Arteries, . . 253 The Pulse, ..... 255 Action of the Veins, .... 257 Action of the Capillaries, . . 258 Causes of the Capillary Circulation, . . 259 Congestion and Inflammation, . . 262 Xll CONTENTS. 264 264 267 268 270 270 273 283 286 Section III.—The Circulating Fluids, The Chyle, • The Lymph, Function of the Lymphatics, Causes of the Lymphatic Circulation, The Blood, . Analysis of the Blood, Pathological changes in the Blood, IV.—Of the Voice—Speech, CHAPTER V. THE PSYCHOLOGICAL ACTIONS—FUNCTIONS OF THE NERVOUS SYSTEM. 291 Section I.—General Considerations, • Natural Division of the Animal Kingdom, • 293 Comparative Structure of the Nervous System in Different Animals, . 294 II.— The Cerebro-Spinal Axis, . • • . -»/ The Spinal Marrow, • 297 Reflex or Excito-Motor Action, . • 300 The Medulla Oblongata, . 303 The Encephalic or Sensory Ganglia, . • 306 The Cerebellum, . 308 The Cerebrum, 309 The Cephalic Nerves, . • • 313 III.—Sensation, ..•••• 317 IV.—Special Sensation, .... 321 Sense of Touch, . . • .321 Sense of Taste, .... 823 Sense of Smell, . 3-^ Sense of Hearing, .... 326 Sense of Vision, .... 332 CHAPTER VI. REPRODUCTION OR GENERATION. History and Development of the Germ, Action of the Male, ...... Action of the Female, ..... Menstruation, ...... Changes in the Ovule before Fecundation, Changes occurring after Fecundation, Development of the Embryo, .... Circulation of the Foetus, ..... Parturition, .... ANALYSIS OF PHYSIOLOGY. PART I. GENERAL INTRODUCTORY CONSIDERATIONS. Physiology may be defined to be the science which treats of the actions peculiar to living, or organized beings. All bodies in nature are susceptible of division into two great classes—the inorganic, and the organic or organized. The former includes the mineral kingdom; the latter, the vegetable and animal. The laws of physics govern the former class, while the latter is controlled by the laws of vitality and intelligence, together with the laws of physics. It is not always easy precisely to define the limits which sepa- rate these different classes of objects, so insensibly do their extremes seem to merge into each other. Thus, although no one could confound an ordinary crystal with an herb or flower, or mistake a tree for a quadruped, he might be not a little perplexed to discriminate between the solid coral, and the rock to which it may be attached; or between one of the lowest polypi, scarcely evincing a rudiment of animality, and a vegetable. Organic and inorganic bodies, nevertheless, exhibit many well- marked points of distinction. 1. In form. In organic bodies, the shape is constant and determinate for every species or race, allowance being made for individuals, and this shape is bounded by rounded outlines; inorganic bodies, on the contrary, are either unde- fined or shapeless in their form, or else occur in crystals, bounded by angles and straight lines. 2. In origin. Organized bodies always 2 14 ANALYSIS OF PHYSIOLOGY. spring from a parent, or germ; inorganic bodies are formed by the aggregation of particles of matter, by virtue of certain forces, as of cohesion, or chemical affinity. 3. In internal structure. Organic bodies are made up of different parts, or organs, each of which has a different texture,—the union of the whole being requisite for the perfection of the being; an inorganic body—a crystal, for-example—may be divided into the minutest fragments, and yet each separate atom will be a perfect representative of the original. 4. In size. The size of inorganic masses is entirely indeterminate; that of organized bodies is, for the most part, restricted within certain limits. Departures from this rule are, however, seen in the lowest order of animal and vegetable life, as in the coral, the sea-weed, &c.; but, in most of these cases, the increase in size is dependent upon a continued production of new individuals, rather than upon a continued development of the same individual. 5. In chemical composition. The peculiarity of the chemical composition of organic bodies depends, not upon the presence of any elementary substances not found in the inor- ganic class, but upon the comparatively small number of these elements entering into their constitution. Of the sixty-two simple or ultimate elements found in the inorganic kingdom, about eighteen only exist in organic bodies ; and of these, only four are regarded as essential, viz., carbon, oxygen, hydrogen, and nitrogen, —the remainder (termed non-essential or accidental) being intro- duced apparently for mechanical or chemical purposes. Some of these are extremely rare; others occur very frequently, and sub- serve important purposes in the living economy; thus, sulphur and phosphorus are found in albumen and fibrin; phosphorus and calcium, in the form of phosphate of lime, give hardness to bones; phosphorus is an integrant part of the brain ; iron occurs as a constant ingredient of the blood; and so on. The tissues of vegetables are found to be remarkably uniform in their chemical composition, consisting of a substance termed cellulose. This is a ternary compound of carbon, oxygen, and hydrogen, the two latter being in the proportion to form water. FORCES concerned in organized beings. 15 The inner wall of the vegetable cell is composed of a nitrogenized substance, believed to be identical with the animal cell-wall. Animal tissues consist essentially of two proximate nitro- genized principles—proteine and gelatine. We shall, hereafter, allude to those proximate constituents of plants and animals, more in detail (Part II.) ; they are cursorily presented here, merely to complete the outline of the sketch intended to exhibit the points of difference between the organic and the inorganic kingdoms.—There are various other points of dis- tinction, such as the mode by which vegetables and animals derive their nourishment from the exterior world, their different functions of digestion, assimilation, secretion, &c.; all of which will be duly noticed in their proper place. CHAPTER I. OF THE DIFFERENT FORCES CONCERNED IN ORGANIZED BEINGS. All the knowledge derived by the intelligence of the exterior world, consists in an understanding of, 1, the properties of matter; 2, the unknown causes of its action, or forces ; 3, the different forms which it may assume under the influence of molecular forces; and 4, the offices or functions performed by it, under its specific forms. The human mind, from its very nature, cannot come into imme- diate, direct contact with the exterior world; all its information must necessarily be derived through the avenue of the special senses—hearing, sight, smell, taste, and touch. These sensibili- ties are placed intermediate between the mind and the external world. Hence a knowledge of the absolute, essential nature of matter can never be attained in the present state of existence, 16 ANALYSIS OF PHYSIOLOGY. inasmuch as the properties of matter alone can be appreciated by the senses. Sensibility is something quite distinct from the mind : it forms no part of the intellect, but is limited to a special nervous apparatus—special for each individual sense. This is proved by the fact that the sensibilities may continue in activity while the mind is suspended, and vice versa ; also, by the existence of sensibility in the very lowest order of animals, in which there is no evidence of the presence of intellect. Now the mind, though its perceptive faculties, is in direct communication with the different sensibilities, and is thus enabled to appreciate the different modifications pro- duced upon them by the different properties of matter. By a process of induction, the mind refers the various pheno- mena of the external world to certain causes ; and if the recurrence of these phenomena be constant, under similar circumstances, the unknown cause is termed a, force. Force, then, is an abstract idea, expressive of the unknown cause of change of condition or state. Forces can only be known by the phenomena which they produce in matter. In mechanics, we speak of the forces of gravitation and cohesion as the unknown causes of attraction—the one between matter, the other between molecules. In thermotics we have to do with the force of heat; in optics with the force of light; in electricity and magnetism, with the forces known under these names. The same thing is true of sound and of chemical affinity. In all the above physical sciences, what are called their laws, are nothing more than the conditions under which their respective forces will act. Conceding then the existence of the above special physical forces, governing inorganic matter, it becomes a matter of inte- resting inquiry how far the same forces and laws can be adduced to explain the phenomena of organized or living beings ; or whether there is in them evidence of the existence of another force, totally distinct in its operations, and quite peculiar in its effects, to which the term vital force might appropriately be assigned. There is abundant proof to sustain both of these propositions:—namely, that many of the phenomena of living beings, are purely physical, FORCES CONCERNED IN ORGANIZED BEINGS. 17 and are consequently, as such, controlled by the forces and laws of physics; again, that in living beings there are displayed certain peculiar phenomena, never found in inorganic matter, and existing only in animals and vegetables endowed with life, and expressed by the evolution of forms out of a formless material. It is to this latter force that it is proposed to restrict the term vital or organic. To the vague and indefinite use of this term in Physiology, is to be traced much of the obscurity and error that have, more or less, been constantly prevalent. It has been too much the habit to confound together all the phenomena displayed by living beings, under the general term of " vital phenomena/' because connected with life, and, because regarded as beyond the reach of human understanding, to ascribe them indiscriminately to a cause equally vague and unsatisfactory,—"vital action." Hap- pily,- however, these false views have begun to clear away before the light of a more exact and rigid mode of investigation; and the student of the present day is enabled satisfactorily to explain many of the apparently intricate phenomena of life, by a simple reference to the well-understood principles of the exact physical sciences. Before proceeding to illustrate this position, it may be profit- able briefly to allude to the doctrine of the Correlation of Forces, —a subject which is, at present, exciting considerable attention, both among physicists and physiologists. From the clearer in- sight obtained within late years into the nature of the phenomena of the physical sciences, the opinion has been gradually gaining ground, that the various physical forces, though apparently differ- ing from each other, are in reality either modifications of one and the same force, or are correlative, or mutually convertible into each other.* * Prof. Grove's treatise on the "Correlation of the Physical Forces," was the first pub- lished work upon this subject. The first edition appeared in 1843. It was followed in Germany by one from Mayer of Heilbronn, in 1845. Within the past year, Dr. Carpenter has investigated the subject, in an able communication to the Royal Society, entitled "On the Mutual Relations of the Vital and Physical Forces." Prior, however, to the appear- ance of any of the above treatises, Professor Jackson, of Philadelphia, had formally stated this doctrine, in an Introductory Lecture to his Course on the Institutes of Medicine, for the year 1837-8, as will be seen by the following extract:—"Physical phenomena, accord- 2* 18 ANALYSIS OF PHYSIOLOGY. It was in the case of electricity and magnetism that this reci- procal relation, or " correlation," was first clearly understood. It an electric current be passed around a piece of soft iron, the latter becomes magnetic, and remains so as long as the current is circulating. On the other hand, a magnet in motion will develop electricity. We thus perceive that the two forces, electricity and magnetism, are mutually convertible, or correlative. The same is equally true of other forces; thus, heat may be developed from electricity, and vice versd. In fact, no one of these forces can be called into action without, at the same time, exciting the other; thus, by retarding mechanical motion, as in friction, there are immediately developed heat, electricity, light, and magnetism. The correlation of heat and mechanic power is familiarly wit- nessed in the effects of steam (water converted into vapour by heat), as a motive power. The attempt has even been made to identify the forces of light, heat, and chemical affinity, by refer- ring them simply to a difference in the velocity of the undulations of the same ether, believed to pervade all space. This idea was founded on the well-known fact, that while the greatest illumi- nating power of the solar spectrum is about its centre, the greatest heating effect is observed just beyond the red ray, where the un- dulations are least numerous; and the greatest chemical effect is produced just beyond the violet ray, where the undulations are most numerous. The interesting question now arises,—is there any identity, or correlation between these physical forces, and those observed in organized or living beings ? In order properly to reply, it will be necessary to take a survey of all the phenomena of living beings, and subject them to a rigid analysis. It will then be found that many of these phenomena—usually termed vital, because con- nected with vitality—are governed by laws precisely similar to those which control organic matter; while a few only exhibit evidence of the influence of a l&w peculiar to living beings, and to ing to the class they belong to, are referred to a few simple laws, as gravity, caloric, am- nity, galvanism electricity magnetism, all of which, it can now be scarcely doubted, are modifications of one great law or force." ^ FORCES CONCERNED IN ORGANIZED BEINGS. 19 which exclusively, we should properly restrict the term law of vitality. We may illustrate this by a few familiar examples. The transformation of the crude albumen into the protoplasmas, or immediate organizable materials for the structure, is an undoubted chemical action; it requires a temperature of about 98°. The circulation of the blood, by means of the propelling power of the heart, aided by the elasticity of the arteries, is a purely physical phenomenon, governed by the laws of hydraulics. Respiration is a combination of physical and chemical actions,—the former con- trolling the respiratory movements of the chest, and the inter- change of gases by endosmose, through the air-cells of the lungs; the latter affecting the condition of the blood circulating through the lungs. Digestion is a function partly mechanical, so far as relates to the peristaltic movements of the stomach and bowels; and partly chemical, so far as concerns the different chemical changes produced in the ingesta. Muscular motion, including locomotion, is essentially a mechanical action; the whole muscu- lar apparatus being, in fact, the mechanical power employed by the economy for the working of most of its functions, under the dynamic influence of the nerve-centres. Secretion is a function partially, at least, under the influence of the physical law of en- dosmose, and of chemical action. Absorption belongs wholly to the domain of physics ; Calorification, solely to that of chemistry. Finally, the apparatuses of vision, hearing, and the voice, are all constructed in the most exact conformity with the physical laws of optics, acoustics, and phonation. Thus we perceive that nearly all the so-called phenomena of vitality—digestion, respiration, circulation, absorption, muscula- rity, secretion, calorification, &c, are controlled by forces identical with those which govern inorganic matter; and these forces, although limited in their operation in living beings, and subserv- ing the one great end of the conservation of the being, are none the less physical because connected with living actions. Let us now examine the question whether the vital or organic force, in its strictest sense, has any identity, or correlation with the above-named physical forces. It will be remembered that we 20 ANALYSIS OF PHYSIOLOGY. restrict the use of the term to express a force exhibited exclusively by living beings. Now, the only phenomena peculiar to living beings are the nervous force controlling muscular contraction, and the power of evolving special, typical forms out of a formless material. As regards the nerve-force, it is obvious that it cannot fall within the above definition of organic force, since it is not found in vegetables, nor is it indispensable even to animal existence; the organic functions of even the higher animals being only indi- rectly under its control. Nervous force is certainly correlative with galvanism or electricity; but it is altogether distinct from the operations of mind, as displayed in the phenomena of the intellect, and moral faculties. The nerve-force is only the dyna- mic excitor of muscular contraction, and has acquired the distinc- tion of a vital force from its necessity as an excitor of the muscu- lar actions of respiration in man and the higher animals. It is then to " the evolution of forms out of a formless mate- rial," that we are to confine our meaning of the term organic or vital force. This force must be present in every organized being, and participate in every life-action. The great variety of forms which is presented in an organized being, owes its origin to one common material, termed plasma, blastema, cytoblastema, &c.; these forms, moreover, owe their constant maintenance and renewal to this same material, which, chemically, is albumen. But, for the production of each special form, this common plasma must first become special, or proto- plasma; thus, it is one kind for muscles, another for nerve-sub- stance, another for bone, &c. As soon as speciality is given to the organizable material,—indeed simultaneously with it in the actual life-actions,—special forms are developed, through the con- trolling, mysterious agency of the germ-power which is manifested wherever organization is going on. As a special form is insured by a special material, so speciality of function is the result of a special form. Indeed, as Miiller observes, material, form, and function must always coexist; they cannot be separated. In this manner it is that every organ of FORCES CONCERNED IN ORGANIZED BEINGS. 21 the body has its specific function. Every living cell is, in fact, a specific organism, performing certain specific actions; the vege- table cell, for example, under the agency of the sun's rays, de- composes carbonic acid, and the animal cells elaborate the various secretions of the body. From a consideration of what has just been said, it will be ap- parent that, though the production of special materials, or proto- plasmas, out of one common material, and the evolution of special forms are consentaneous acts, they are, nevertheless, quite dis- tinct. The first is really chemical; it comprises the transforma- tion of the crude material of the egg—albumen—into fibrin, gelatin, neurine, and the various other proximate elements of the tissues. But it is not common chemical action; it is organ ico- chemical, since it is controlled by.the germ-force; without this latter agency, the crude material, instead of undergoing the higher developments just mentioned, would suffer ordinary chemical putrefaction, as is witnessed in an unfecundated egg when exposed to the proper temperature for incubation, and to atmospheric air; decomposition is the only result. Thus far, then, we may admit the correlation between the organic force and chemical action and heat. But, certainly, there is no identity between that higher power of the organic force, which determines the production of forms after a special type, and any of the ordinary physical forces, heat, light, electricity, &c.—they are entirely distinct, and are only correlative, so far as has been just explained. It will here be proper to observe that the above views, which are substantially the same as those taught by Prof. Jackson, in his public lectures, do not altogether accord with the opinion of Dr. Carpenter, as exhibited in the last edition of his works on Physiology, and in his paper on " The Mutual Relations of the Vital and Physical Forces," already alluded to. Dr. Carpenter's idea is that, as in Physics, one force is converted into another through the medium of a certain form of matter, or material sub- stratum,—as when electricity is converted into magnetism through iron, or heat into electricity through a combination of bismuth and antimony, so "all the truly vital phenomena, however diver- 22 ANALYSIS OF PHYSIOLOGY. sified, are but results of the operation of one and the same force, whose particular manifestations are determined by the nature of the material substratum through which it acts; the same funda- mental agency producing simple growth in one case, transforma- tion in another, multiplication in a third, mechanical movement in a fourth, whilst in a fifth it developes nervous power, which may itself operate in a variety of different modes." Under this view, it will be perceived that the ordinary physical forces, light, heat, electricity, &c, are regarded as capable of being converted into vital force, by acting upon organic matter under certain conditions. It does not recognise any peculiar vital force, characterized by the " evolution of forms from a formless mate- rial." The vital or organic force acts upon the amorphous organic mass, modifying it so as to produce secondary forms, and develope it into a new structure. As will hereafter be shown, all organized beings, from the lowest to the highest, have their origin in cells, or rather in germs, out of which the cells are formed. These cells grow by appropriating the surrounding materials; thus the vege- table-cell has the power of decomposing water, carbonic acid, and ammonia, under the influence of the sun's light, and of combining the carbon, oxygen, and hydrogen, so as to form the gummy or starchy product, which serves as the pabulum of the vegetable tissues. It is possible that thus far the act may be simply che- mical, resulting from what is termed the action of catalysis, in which one body exerts an. influence over two other bodies, so as to occasion their union or separation, without itself undergoing any change. Thus, it has been conjectured that the germinal molecule may exert this kind of an influence over the elements of the water and carbonic acid, with which it is in contact. The animal cell does not possess this power; it can only modify, or work up the material submitted to it. The dynamic forces are totally distinct from the vital. They are connected with the excito-motor nervous system, and are dis- played by the muscles as their appropriate agents. As many im- portant functions of the economy are performed through the ESSENTIAL CONDITIONS OF LIFE. 23 agency of the dynamic forces, they will require a separate notice in a subsequent part of this work, (Part IV.) CHAPTER II. CONDITIONS FOR THE DISPLAY OF THE VITAL FORCE. The organic or vital force is not only the cause of all original formative action in the development of the germ, it also presides over its whole future growth, being inseparably connected with each of the successive stages of the process of nutrition. It is not, however, self-acting; but is dependent upon certain exterior agents for power to develope it into activity. A seed, for in- stance, although possessing a dormant vitality, or in other words alive, will never germinate, unless exposed to a proper heat, to moisture, oxygen, and probably also light. Some of these condi- tions required for the display of vital force are so indispensable, that they have received the name of the essential conditions, or laws of life; they are, 1. The presence of a germ; 2. A plastic or organizable material,—albumen for animals, dextrine for vege- tables; 3. A certain amount of caloric, differing for different genera of plants and animals; for man, it is from 98° to 100°; 4. Oxygen, in the proportion in which it exists in the atmosphere; 5. Moisture;—a certain amount of water is requisite to give due fluidity to the various matters for nutrition and secretion. To these may be added, as of less essential importance, Light, which is indispensable to the functions of vegetables, though not to the evolution of their forms. Since the whole of organic life is but a repetition of its first acts, it follows that the first five of the above conditions are always essential. If any one of them be absent for a length of time, 24 ANALYSIS OF PHYSIOLOGY. disease must be the result; and if all of them be absent, death must inevitably follow. We will now examine into these " essential conditions of life" more in detail. SECTION I. OF THE GERM, AS AN ESSENTIAL CONDITION OF LIFE. The germ is perhaps the most important of all the indispensable conditions of life, since in it resides that wonderful power of developing special forms according to some particular type. The germ-force may consequently be regarded as identical with the vital or organic force already described. If it be absent in the process of organization, although all the other essential conditions of vitality be present, such as a healthy plasma, oxygen, and a normal temperature, no form can be evolved, but the result will be simply the ordinary play of the chemical affinities, terminating in decomposition. This is well illustrated in an egg which has been laid before impregnation by the male : if this be submitted to the temperature proper for incubation, it only undergoes putre- faction : wanting merely the germ-force, its otherwise healthy material is incapable of taking on organization. At its commencement, the germ is but a microscopic point, scarcely visible by the highest magnifier. It is always the result of the union of two distinct cells, the ovo-cell and the germ-cell; and it is moreover transmitted to every part of the organism, by being split up or divided by the process termed segmentation, by which it first divides into two, then each one of these again into two • and so on, constantly doubling, until the whole is broken up into countless granules, each one of which must of course be endowed with all the qualities of the original germ, and thus becomes, in point of fact, a true germ or nucleus. In the eggs of birds and reptiles, it is only the cicatricula (which corresponds with the TnE GERM, AS A CONDITION OF LIFE. 25 ovum of mammalia) that undergoes this process of segmentation; the }'olk merely serves as a store of nourishment for the embryo. The name of mulberry mass is sometimes given to the aggregated mass thus produced. Each little granule augments by assimila- tion from the surrounding materials, and shortly becomes enve- loped by an organic membrane, by which it is constituted a cell; within which the germ, or nucleus is contained. Each cell thus formed is an independent living organism, per- forming its allotted functions, and living through its allotted space of life. Many animals and vegetables never advance farther than this point of development; as is witnessed in the monads, and in the Protococcus nivalis, or red snow of the Arctic regions. The fact that the germ is always the offspring of two distinct parents, will account for the complexity of its composition. In the very earliest period of its development, when the germinal membrane begins to form upon the germinal mass, we find it consisting of two distinct layers; the inner, or mucous one being destined to give origin to all the organs of organic life—as the alimentary, respiratory, and circulatory organs; while the outer layer developes the organs of animal life—as the nervous, muscu- lar, and osseous systems. What are termed nuclei of cells or tissue-germs, are the lineal descendants of the primordial or original ovo-germ : they are to the respective tissues what the ovo-germ is to the whole being. As they are endowed with germ-force, they are the instruments for manufacturing the various protoplasms; hence any cause pro- ducing an arrest in the development of the tissue-germs of any particular tissue will result in atrophy of that tissue; whilst hypertrophy would be the result of their excessive production. They are the agents by which all the different organs are main- tained in their normal condition, since they replace what is con- stantly being lost by ordinary disintegration. Farther, they are the instruments by which alone injuries are repaired, and the loss of substance supplied, provided the structure required be of a simple homogeneous character, as the areolar tissue; or even an entire limb of one of the lowest order of animals. In tissues of 8 26 ANALYSIS OF PHYSIOLOGY. greater complexity, as the nervous, and muscular, perfect repara- tion becomes much more difficult, if not impossible. The cause of this difficulty is by Mr. Owen ascribed to "an exhaustion of the germ-force in the original production of these tissues, and that, consequently, their loss of substance cannot be supplied." Now this can hardly be the true explanation, since, if the germ- force were really exhausted at the first, the forms of the structures could not be constantly maintained throughout life. It may rather be ascribed to the impossibility of keeping the parts in that con- dition of absolute repose which they enjoyed at their first forma- tion. As an evidence of this, we occasionally witness recovery from paralysis by perfect rest for several years. In some of the complex tissues we find two distinct sets of ac- tions, the results of the germ-force. In the epithelial tissues, for example, the germinal centres of the basement-membrane (or the tissue-germs) have for their office simply to constantly develope the chemical, or epithelial cells; whilst these latter possess no re- productive power, but are destined simply to secrete from the blood, in the performance of which they die, and are cast off. The same is true of muscular structure ; the cells destined to produce mus- cular contraction undergo no histological change, and are destitute of the power of self-production, their constant destruction being supplied by the nuclei of the sarcolemma, which, on the other hand, possess no contractile power. It can now readily be understood how difficult it would be to repair any considerable loss of such complex structures, on account of the destruction of the tissue-germs —the only instruments for the repair. In such cases, a fibrous matter is usually supplied, as the bond of union. As in the germ resides the force which developes the whole future being, so through it, also, are transmitted all the peculiari- ties of hereditary descent, whether of a healthy or diseased cha- racter. The latter are especially witnessed in scrofulosis, tubercu- losis, and idiocy. THE PLASMA, AS A CONDITION OF LIFE. 27 SECTION II. OF THE PLASMA OR ORGANIZABLE MATERIAL, AS AN ESSENTIAL CONDITION OF LIFE. The second indispensable condition of life is the presence of a proper organizable material, or plasma, on which the organic force may act, and out of it construct the different tissues and organs of the body. In vegetables this material consists of dextrine ; in the egg it is contained in the yolk, which consists chiefly of albumen ; in animals, and in man it is found in the blood. The liquor sanguinis may in fact be regarded as a concentrated solution of all the materials necessary for the construction of the organs and tissues, as well as for the secretions. The corpuscles of the blood are not directly concerned in producing the plasma; though in- directly they act by transforming the crude albumen into fibrin, a function assigned by most physiologists to the red corpuscles; the latter are intimately connected with the nerve-forces. The plasma contains albumen and fibrin; but neither of these proximate constituents, as such, can be said to enter into the com- position of any organ; even the fibrin of muscles, according to Liebig, differs from that found in the blood. Moreover, neither gelatine nor neurine have ever been found in the blood. Hence, it appears that all the immediate materials for the formation of tissues—or the various protoplasms—do not pre-exist in the blood, but are evolved from it by the agency of the germ-force. This evolution of the protoplasms occurs simultaneously with the evo- lution of the various forms; and this double process is incessantly taking place, to compensate for the incessant disintegration of the tissues, in the acts of life. The constant supply of this reparative material is, as we have seen, derived from the blood, which in its turn is supplied from the food taken in. Now, the daily amount of the waste or disintegration of the azotized tissues, in an adult man, is from two to three ounces; this must all be supplied from the food through the blood, since 28 ANALYSIS OF PHYSIOLOGY. animals are unable to manufacture a particle of azotized matter; this is the exclusive province of vegetable cells : animals can only modify it, or cause it to assume different forms. The greater part of man's food—nearly seven-eighths—as presented to us by nature, contains no nitrogen, and is destined to support animal temperature, by undergoing oxidation, or slow combustion, in the body. From this abundant provision for the maintenance of animal heat, we may infer its great importance to the economy; it is essential, as we shall hereafter find, for the conversion of the common plasma into the various protoplasmata. The food as swallowed into the stomach is not fit for the pur- poses of nutrition without first undergoing the process of digestion, by which all the albuminous principles are converted into a com- mon soluble matter, named by Mialhe albuminose. From its solu- bility and miscibility with the blood, this matter is capable of being imbibed immediately into the blood-vessels of the stomach; and in this way probably it is that some of the azotized portion of food is disposed of. Plasma may hence be considered as the transitional stage be- tween crude food and organized structure. It has already been pointed out that animals derive all their azotized food from vege- tables, since they themselves create nothing; farther, the matter thus presented for food requires that its ultimate elements, carbon, oxygen, hydrogen, and nitrogen, should be in the exact proportion of those of albumen ; otherwise, even though all the elements were present, the substance could not be used for food, as is seen in the case of quinia, morphia, caffein, &c.; these latter are powerful medicinal agents, acting on the nervous centres, but are quite destitute of nutritive qualities. We may infer from these facts the great importance of a due attention to dietetics. For the pre- servation of health there must be from two to three ounces of nutritious (albuminous) materials, per diem, in the food of adults; yet this is very often neglected, especially by those of sedentary habits, who are apt to substitute for it the inordinate use of coffee and tea, and thus bring on the effects of inanition. As the food which furnishes the plasma is derived from the ex- OXYGEN, AS A CONDITION OF LIFE. 29 terior world, it is liable to defect in several ways; as, first, from an absolute deficiency of it, arising from the use of innutritious or otherwise improper food, from chronic diseases of the digestive organs, or from marasmus; secondly, from the existence of certain constitutional disease, as tubercle, scrofula, cancer, &c.; thirdly, by absorption of noxious matters from without, as the various con- tagious viruses, miasmata, typhoid matter, &c.; these all acting as ferments in the blood, must transform the true plasma into their own peculiar matter; and the efforts made by the system to throw off this morbific matter, constitute disease; fourthly, by the introduction of certain kinds of animal virus into the blood, as from the bite of a rattlesnake, viper, &c.; fifthly, by the gene- ration of a poison in the blood, as is witnessed in the blood of animals overdriven in hot weather ; the blood of such animals if inoculated into a healthy animal would be likely to produce death; sixthly, the blood may be poisoned, and the plasma of course de- teriorated, by the retention of noxious matters designed to be re- moved by the excretions; thus the retention in the blood of urea, uric acid, bilin, sugar, &c, is often the cause of disease. Some of the substances found in the blood are undergoing constant de- composition in the normal state; as lactic acid and the lactates, their carbon and hydrogen serving as fuel for combustion to pro- duce animal heat; they may occasionally, however, accumulate in the blood. SECTION III. OF OXYGEN, AS AN ESSENTIAL CONDITION OF LIFE. The presence of this gas throughout nature is indispensable. For living animals and plants the proportion of it required is just that in which it exists in the air. The composition of the atmosphere is by weight, seventy-seven parts of nitrogen, and twenty-three of oxygen; by volume, about 3* 30 ANALYSIS OF PHYSIOLOGY. eighty parts of nitrogen and twenty of oxygen. There are also from four to six parts of carbonic acid in every thousand of air, together with a variable amount of moisture, and a minute quan- tity of ammonia, especially after a thunder-storm. A most abundant provision is made for the supply of every living being with this most necessary element of life. The whole surface of the globe is covered over with a vast aerial ocean, which exerts upon it a pressure of nearly fifteen pounds to every square inch, but diminishing in density in proportion to the elevation from the surface. It is liable to contamination from various sources, as respiration, combustion, putrefaction, fermentation, and various sorts of exhalations; nevertheless, the accumulation of any noxious matters in a circumscribed portion of air is pre- vented by the " laws of diffusion" of gases, as shown by Mr. Gra- ham; the diffusibility of any two gases being "inversely to the square root of their density." The air of cities is always more impure than that of the open country; this is the cause of the languor and depressing sensations experienced in towns during hot weather, which is not the case in the country, although the temperature may be quite as high. Hence, too, the greater mor- tality of large cities, it being from thirty to fifty per cent, more, for the same disease, in the city than in the country; besides the number of cases of the same disease being about forty-five per cent, more in the cities, than in an equally numerous rural popu- lation. The whole quantity of air consumed by a healthy adult man in twenty-four hours amounts to about 266 cubic feet; of this, twenty- five ounces (Liebig says thirty-seven) consist of oxygen. The amount of solid carbon eliminated from the body in the form of carbonic acid amounts, according to Liebig, to 13-9 ounces* but this is by many considered too high; they estimate that ten or eleven ounces more nearly express the true amount of carbon ex- creted per diem, by both the lungs and skin. There is a mutual relation between the amount of oxygen in- haled and that of carbonic acid expired ; the latter being regulated by the former. From ten to fifteen cubic feet of carbonic acid OXYGEN, AS A CONDITION OF LIFE. 31 are exhaled by a healthy adult man in twenty-four hours; now, if the quantity of oxygen inhaled be diminished from any cause, whether by contamination or rarefaction, the effect will be the retention of the carbonic acid in the blood, producing injurious results, and even asphyxia, when it reaches a certain amount. In these cases the danger is vastly greater if the accumulation of the carbonic acid in the air is at the expense of the oxygen, than if there was merely a surplus of carbonic acid, the oxygen remaining undiminished. One per cent, of carbonic acid in the atmosphere is sufficient to produce unpleasant results, such as headache, lassi- tude, &c.; and twelve per cent, is sufficient to cause death. Oxygen is the great decomposing agent in the animal economy. .Inhaled, in the act of respiration, into the lungs, it passes into the circulation; and in the capillary region it enters into combination with the various elements of the tissues, thus causing their dis- integration, and producing the different effete matters thrown off from the economy. Especially, is the oxygen thus inhaled dis- posed to unite with carbon and hydrogen, giving rise to carbonic acid and watery vapour, and producing, as a result, a certain amount of heat in the system, known as animal temperature. The degree of heat evolved by this species of slow combustion is precisely equal to that produced by the rapid combustion of the same quantity of hydro-carbon out of the body. Heat is also generated in the germination of seeds (as witnessed in the malting of barley), and in the flowering of plants ; oxygen being essential to both processes,—a species of slow combustion or oxidation taking place in both. The great importance of oxygen to the animal economy is too frequently lost sight of in the construction of buildings for the accommodation of large numbers of persons. When it is remem- bered that every adult vitiates 250 to 300 cubic feet of air in respiration, in twenty-four hours, and that this quantity must be actually renewed, the importance of proper ventilation will be rightly appreciated. But it is not only the carbonic acid thrown off by the lungs that contaminates the air, but this is still farther aided by the animal exhalations which are constantly passing off 32 ANALYSIS OF PHYSIOLOGY. from the body. These two causes combined have been the prolific source of typhus fever, and hospital gangrene. Another result of the vitiation of the atmosphere by these causes is the increase thereby given both to the number of cases, and the mortality of any epidemic; it is sure to be particularly violent in the crowded, filthy courts and alleys of cities, because, in such situations, the forces of life are sooner exhausted. Atmospheric variations, though not generally noticed by persons in vigorous health, are very sensibly felt by the invalid. The different effects experienced by the latter in breathing the more rarefied air of the mountains, and the comparatively denser atmo- sphere of the sea-side, is a proof of this. Chronic diseases are generally ameliorated when the barometer is high, indicating fair weather, and a heavy atmosphere. Under certain conditions, the atmosphere exhibits evidence of the existence of a peculiar substance called ozone. Various opi- nions are held in reference to this principle; some consider it to be a new element; others, as Berzelius and Faraday, regard it as only an allatropic condition of oxygen ; by others, again, it is considered a peroxide of hydrogen, expressed by H04, or H05. Ozone is also perceived in the spark procured from the electric machine, and when phosphorus is in contact with moist air. Its properties are quite peculiar : it is the most powerful oxidizing body known; polished silver becoming speedily tarnished on ex- posure to it. To its oxidizing agency may be ascribed the forma- tion of the nitrates and sulphates in nature. It is the most powerful bleaching agent known, the bleaching property attributed usually to the sun's rays being, in reality, due to it. Through the same oxidizing agency, it is a powerful disinfectant. In this way it proves useful in the atmosphere of cities, and for this reason it cannot be discovered in such an atmosphere, because it has been consumed in combining with the noxious emanations. It is most abundant in winter, when the ground is covered with snow; also in the open country, especially on the sea-side • also immediately after a thunder-storm. Its presence can be detected by moistening a piece of paper HEAT, AS A CONDITION OF LIFE. 33 with a solution of ten grains of starch and one grain of iodide of potassium in a hundred grains of water; this paper is dried, and when wanted for use, is to be moistened in water, and then ex- posed to the air; the depth of blue colour is regarded as indicative of the amount of ozone present. SECTION IV. OF HEAT, AS AN INDISPENSABLE CONDITION OF LIFE. The great importance of heat to all living beings is exhibited in the abundant provision made for it by nature; its amount being always in the ratio of the vital processes both of vegetables and animals. Its influence upon vegetation is witnessed on a large scale, by comparing the barrenness of the polar regions with the luxurious growth of the tropics ; and also in the alternations of winter and summer in temperate climates. Vegetables appear mere affected by a withdrawal of heat than animals, because they have no power of generating caloric for themselves, excepting at certain periods, and in certain organs which do not impart it to the rest of the structure. The different genera and species of vegetables are endowed with different powers of enduring heat and cold. Ac- cordingly we find peculiar races adapted to each of the varieties of climate upon the earth's surface; and when any one of these is removed from its own appropriate temperature, it either perishes, or its nutritive processes are materially interfered with. The plants capable of enduring the lowest temperature are the Cryptogamic tribes, as ferns, mosses, lichens, &c.; and accord- ingly, the proportion of these to the Phanerogamia, or flowering plants increases as we advance from the equator towards the poles. Among flowering plants, moreover, the greatest endurance of cold is found in those which most nearly resemble the Cryptogamia in development,—as the grasses, rushes, and sedges; hence these 34 ANALYSIS OF PHYSIOLOGY. are found to constitute about one-eleventh of the whole of the flower- ing plants in the tropics, one-fourth in the temperate zones, and one-third in the polar regions. The ratio of the Gymnospermic group of exogens—as the fir and pine—increases in like manner. The temperature of a place is not only regulated by its distance from the equator, but also by its elevation above the sea. The snow-line, or the region of perpetual snow on mountains, will of course vary according to the distance from the equator; thus, under the equator, it is from 15 to 16,000 feet above the level of the sea; on the Swiss Alps, about 8000 feet. The elevation, however, is very much affected by local circumstances, as the proximity to a large expanse of sea or land; the former condition rendering the climate much colder at equal elevations. The evaporation of moisture which is constantly taking place from the surface of plants enables them to resist, to a great ex- tent, the consequences of excessive heat. This ability, however, depends upon their receiving a due supply of water. If this sup- ply be adequate to the demand, all the vital operations will be stimulated by the heat to increased energy; and unusual luxuriance of growth may result. But if the supply of water be inadequate, then the plant either withers and dies, or else its tissues become dense and contracted; as is seen in the stunted shrubs of the sandy deserts of the East. The highest temperature observed by Humboldt in the soil of tropical climates was from 126° to 140°. The influence of a very low temperature is well known to be fatal to most kinds of vegetation; although there may frequently be a complete cessation of the vital processes, or in other words, they may be dormant, without the vitality being lost,—a rise of temperature being only requisite, again to call them into action. It is doubtless through chemical or physical agency that cold proves destructive to vegetation, causing congelation in the fluids, and rupture of the cells, by the expansion produced in freezing. Also, there may be a separation caused between the constituent parts of the juices of the plant by the act of freezing, which may be incompatible with its functions. Hence we find that the suc- culent plants, which abound in fluids, are most injured by oold • HEAT, AS A CONDITION OF LIFE. 35 and that the young shoots are more affected than the branches or trunk. Again, the viscid nature of the juices of a plant may enable it to resist the congealing influence of cold; hence the Pines, and other resinous trees are well adapted to extremely low temperatures. It also appears that seeds are capable of enduring an exposure, without injury, to a temperature which would be entirely fatal to growing plants of the same species; this arises, no doubt, from the closeness of their texture, and the minute quan- tity of moisture they contain. The influence of heat upon animals is of equal importance with its effects on vegetables; though it is exerted in a very different manner, from the fact that most animals have the power of gene- rating heat within themselves, totally independent of the external temperature. Still, it is very easy to show that if the conditions necessary for the production of animal heat be interfered with, the animal will as certainly suffer, or even perish, as the vegetable. Animal temperature is the standard by which we judge of the internal organic actions of animals. Like ordinary heat, it is the result of a process of combustion, or oxidation; the fuel consumed being chiefly the carbon and hydrogen of the food. From thirteen to fourteen ounces of pure carbon, per diem, are required in the food of an adult. This will be more fully explained hereafter. (Part. IV.) Heat subserves two very important purposes in the animal economy; first, it is indispensable for the production of the various protoplasmata out of the common plasma, and likewise for the evolution of forms, and secondly, it developes mechanic power by being converted into the nerve motor force, through the medium of the nerve-centres. The correlation of heat and mechanic force has already been pointed out. M. Joule ascertained that the de- gree of heat required to raise one gramme (15 grs.) of water, one degree is equivalent to the mechanic force necessary to elevate a weight of 432 grammes (13 £ oz.), one metre. The manner in which animal heat is produced will be spoken of hereafter; it is sufficient here to remark that this power is not equally possessed by different animals; a circumstance which has 36 ANALYSIS OF PHYSIOLOGY. occasioned the division of them into the two classes of warm- blooded and cold-blooded. It is from their different capacities for generating heat, that animals are adapted to varieties of climate; those which possess this capacity to the greatest degree being always found in the coldest countries; those, on the other hand, which have the capa- city least, being placed in tropical countries. Such animals can- not bear a removal to different climates, unless the temperature be artificially regulated, so as to resemble that to which they were accustomed. The human race is capable of enduring variations of climate much better than animals; though even man requires time to become accustomed to changes of this sort. It has been satisfactorily demonstrated by the recent experi- ments of Chossat, that the reduction of the temperature is the immediate cause of death, in starvation. This, he proved by a series of experiments upon birds; and he found that the reduc- tion of temperature was quite regular from day to day, so long as any fat remained upon the animal; but as soon as this was ex- hausted, the temperature rapidly fell, and the animal soon died. But if, at this point, it was subjected to artificial heat, it was immediately resuscitated; its own temperature rose, and if nourish- ment was given it, a complete restoration to health ensued. This affords a valuable practical hint in the treatment of diseases of ex- haustion, in which the great lowering of the temperature is the immediate cause of death. The proper treatment in such cases, is to sustain the temperature of the body, both by the application of external heat, and the judicious administration of alcohol, which, from its chemical composition, is admirably adapted to furnish materials for the process of internal combustion—the usual source of animal caloric. Among the warm-blooded classes of animals, there are some which possess the peculiar property of losing the greater part of their power of generating heat at stated times; during which their temperature is reduced very nearly to that of the surrounding medium, and their vital functions become nearly, if not entirely, dormant, The term hybernating is applied to such animals ; and HEAT, AS A CONDITION OF LIFE. 37 this condition appears to be as natural to them as sleep, and as periodical in its return. An animal in the state of hybernation closely resembles a cold- blooded animal, so far as regards its dependence for heat upon the surrounding medium; but it differs from the latter in the fact of not retaining its functional activity at a reduction of its tempera- ture, which is entirely natural to the other. The different stages of Insect life appear to be very considerably influenced by temperature. In the larva state of insects, the tem- perature is but very slightly elevated above the external air. In the pupa or chrysalis state, which is one of perfect rest, the tempe- rature is scarcely above that of the atmosphere. But in the fully developed insect, we find a considerable elevation of temperature attained, varying, however, in different species. Now, the deve- lopment of the larva from the egg may be either hastened or re- tarded, simply by raising or lowering the temperature; and the development of the insect from the pupa state may be influenced just in the same manner. As respects the degree of heat which animals can sustain com- patible with life, we find a difference among the different tribes. The higher classes and man seem capable of great endurance. Thus, instances are recorded of individuals sustaining a tempera- ture of 350c to 500° for a short time, with proper precautions. In such cases, however, the real heat of the body is but very little elevated; the copious evaporation from the surface having a tendency to lower the temperature. But if this evaporation be prevented, either by saturating the air with moisture, or by not supplying a sufficient quantity of fluid within, the heat of the body then rises, and very shortly death ensues. By experiment, it has been found that an actual rise in the temperature of 9° to 13° above the normal standard, is sufficient to destroy life. As regards the greatest reduction of temperature consistent with animal life, we have already seen that there is a great dif- ference among the various species. As an extreme case, we may cite an instance that occurred in one of the Arctic voyages, of several caterpillars having been exposed to a temperature of 40° 4 38 ANALYSIS OF PHYSIOLOGY. below zero, and so completely frozen, that they resembled lumps of ice; yet, when thawed, they resumed all their movements. One of them was frozen and thawed four times, and afterwards underwent the usual transformation into a chrysalis and moth. In the same way, fishes that have been completely frozen in ice, so as to be brittle, have revived on being thawed. Spallanzani kept frogs and snakes in an ice-house for three years; at the end of which they revived, on being warmed. SECTION V. OF LIGHT, AS A CONDITION OF VITAL ACTION. The importance of this agent in the organic world is not, gene- rally speaking, properly estimated. We may form some idea of its value from the fact, that it is only by its influence that vege- tables exert the wonderful process of converting inorganic matter into an organic compound. The simplest example of this is to be seen in the formation of the " green matter" upon the surface of standing water, or upon damp walls or rocks, under the action of the sun's light. This matter is now known to be a plant, con- sisting of cells in different stages of development. These cells are evidently produced from pre-existing germs, and not from a direct combination of the inorganic elements; as is proved by entirely freeing the water, and also the air in contact with it, from all organic matters; when this is done, the strongest light produces no effect upon the water. That light, and not heat, is the chief cause of the change, is proved by the fact that no degree of heat is sufficient, if light be absent; but a very moderate amount of heat will suffice, if light be present. Prof. Draper has clearly proved by experiments upon the dif- ferent colours of the solar spectrum, that this force resides most LIGHT, AS A CONDITION OF LIFE. 39 in the yellow ray, or that possessed of the greatest illuminating power. The changes which take place when the above conditions are present, consist in the decomposition of the carbonic acid by the cells of the plant, the setting free of oxygen, and the appropria- ting the carbon; which last, when united to the elements of water, constitutes the chief part of the vegetable fabric. It is not quite certain how far the agency of light is necessary in the absorption of nitrogen, which is requisite for the formation of the azotized principles of plants. Now, precisely the same series of changes takes place in the cells of the most complex plants; their structure is increased, or they grow, by this same power of decomposing the carbonic acid through the agency of light: this may be easily shown by allowing seeds to germinate in the dark; the young plants will live for a short time, but they do not increase in weight, though they do in bulk, in consequence of absorbing water. It is only the green surfaces of the leaves, or young shoots of plants, which possess this decomposing power; so that, when these parts decay or fall off, this power ceases also, and a converse operation goes on, namely, the absorption of oxygen, and the giving out of carbonic acid. Thus, the leaves act as the digestive organs of the plants, preparing products which are conveyed to all parts of their struc- ture, by means of the descending sap, so as to become the mate- rials for their nutrition. There is another process quite distinct from this, which is con- stantly going on in plants—their respiration. This is essentially the same as the respiration of animals; oxygen being absorbed, and carbonic acid being given out. It is carried on chiefly by the dark surfaces of the plant, and not at all by the green leaves. During daylight, it is not obvious in a healthy plant, on account of the preponderance of the other function; but it is manifest in the dark, and when the plant becomes unhealthy, or when about losing its leaves. It is generally observed that the vegetation of places, where there is a large amount of carbonic acid present, is unusually 40 ANALYSIS OF PHYSIOLOGY. luxuriant, provided the sun's light be unclouded; and there is strong reason for believing, that in the earlier epochs of the earth's history, the atmosphere contained much more carbonic acid than it does at present; and, in this way, we may account for the enormous fossil vegetable remains, for instance, of ferns which attained the size of perfect trees. In the same manner we may account for the formation of the vast beds of coal, a substance exclusively of vegetable origin. The influence of light is also felt upon the exhaling power of the leaves. Most of the watery portions of the ascending sap are thrown off by the leaves, by a process of exhalation; this process goes on rapidly under the action of light, which stimulates the stomata, or little orifices in the cuticle of the leaves, to expand so as to allow the fluid to pass out. During the early stages of the germination of plants, the pre- sence of light is rather injurious than otherwise. This arises from the fact that, at this time, a converse change from the one above alluded to takes place; carbonic acid is given out, and oxygen absorbed. But as soon as the cotyledons are unfolded, immediately the process of fixing carbon is commenced. All plants do not require the same amount of light for their develop- ment ; those which have thick and succulent parts generally need most, and hence grow in the most open and exposed situations. The cryptogamous plants require less, and are, therefore, met with in dark and sheltered places. The only exception to the general law, that growing plants re- require the stimulus of light, is in the case of the fungi; and this may be easily explained, by the fact that their food is supplied to them by the decomposition of the substances in which they grow, and not from the atmosphere; and the rapidity of their interstitial changes involves a high amount of respiration, by which carbonic acid is eliminated, and oxygen absorbed, just as in the germinating seed. The part performed by the fungi, and many of the moulds which attach themselves to decaying vege- table and animal matter, and feed upon their materials, is highly important in reference to the purification of the atmosphere; LIGHT, AS A CONDITION OF LIFE. 41 hence they have been, not inappropriately, named Nature's sca- vengers. We thus observe a beautiful balance throughout Nature between vegetables and animals; the one appropriating what the other gives out. The organic functions of animals do not seem to be so much under the influence of light as those of vegetables; because ani- mals do not perform the same acts of combination from the inor- ganic kingdom, but make use of the products already prepared for them by plants. Hence the necessity for light is not so great. Still there is every reason to believe, that the colours of animals are very considerably influenced by their degree of exposure to light. In this way we may account for the dark skins of the in- habitants of the tropics—the permanency of the hue being pro- duced by the continued action of the stimulus, from one genera- tion to another. In the same way, the brilliancy of colours seen in most of the birds and insects, as well as of the foliage and fruit, of tropical climates, appears owing to the brightness of the light; for it is known that if birds of a brilliant plumage be reared by artificial temperature in colder climates, they never fully acquire the same bright colours. The development of animals is also much influenced by the amount of light to which they are exposed; this is particularly the case with the lowest animalcules, as those generated in water containing organic remains ; their number surprisingly increasing when the light is bright. Dr. Edwards has shown that the deve- lopment of frogs from the tadpole state may be entirely arrested, if the animals be secluded from the light. There is no question that the full development of the human race is greatly influenced by light. Thus we may witness the injurious effects resulting to the inhabitants of large manufacturing towns, where whole families are often pent up in cellars, or in narrow alleys. Here, to be sure, the individuals suffer from want of ventilation, and from bad diet; but we have only to contrast the pale sickly skins of such persons, and more particularly of those who pass most of their lives in deep mines, where they become completely etiolated 4* 42 ANALYSIS OF PHYSIOLOGY. or blanched, with the ruddy complexion of the sailor or farmer, to perceive the influence of light. Among the "conditions of life" it is often customary to consider Moisture ; this has already been incidentally alluded to under the head of the plasma ; and it will be treated of more in detail here- after under the head of the Inorganic Constituents of the Body. A few remarks may not, however, be out of place in this con- nexion. SECTION VI. OF MOISTURE, AS A CONDITION OF VITAL ACTION. The necessity of water as a solvent has already been alluded to. It is equally essential to both vital and chemical action. It is impossible that nutrition should take place without the aliment being first reduced to the fluid state, so as to be absorbed into the system; and again, the different solid matters of the secretions and the excretions must become fluid before they can be elimi- nated ; and these changes are accomplished solely by the agency of water. The importance of the fluids may be inferred from the great proportion they bear to the solids, in organized beings. Thus the amount of water entering into the composition of man, amounts to ninety per cent. Again, the fluids invariably precede the solids in their formation, which is also an evidence of their greater importance; since, by the law of development, the portion of an organized being which is first produced, is regarded as the most essential, and as the efficient cause of those which succeed it. There are certain animals which appear to consist almost exclu- sively of fluids, as the jelly-fish, one of which, weighing fifty pounds, may be dried down to a weight of only as many grains. There are parallel instances among plants, in the case of certain fungi. Although no vital action can go on without the presence of a MOISTURE, AS A CONDITION OF LIFE. 43 certain amount of moisture, still there are instances among the lowest tribes, both of animals and vegetables, where the entire loss of the fluids merely produces a state of dormant vitality, in which condition they may remain unchanged for any length of time. Among vegetables, we have examples of this in certain mosses and hepaticse, which may be completely dried up, and yet be made to resume their verdure on being moistened. In like manner, the wheel-animalcule may be dried upon a piece of glass, and so preserved any length of time ; but, on being mois- tened, it will become as active as ever. It appears, also, that many of the cold-blooded animals are reduced, by a moderate deficiency of fluid, to a torpid condition, similar to that produced by cold. Many of the mollusca, and even some fishes, exhibit this property, becoming torpid during the heat and drought of summer, but resuming their activity on the approach of wet weather. As the various animals and plants are differently constituted in regard to the amount of fluid contained in their tissues, so are they found dependent, in very different degrees, upon external moisture. There is a beautiful adaptation of plants, particularly, to different situations, with this view; thus we find the Cacti and Euphorbiae of the tropics growing in the driest and most exposed situations, often upon the bare rocks. These plants absorb a great deal of moisture, but exhale very little. On the other hand, those which grow in damp, sheltered situations, exhale moisture almost as fast as they imbibe it. Animals appear to be less influenced by external moisture than vegetables; in conse- quence, no doubt, of the mode by which they are supplied with moisture being so very different from that on which plants are dependent. Still, the hygrometric state of the atmosphere must produce some modifications, though they be not very obvious. It acts chiefly, by either increasing or diminishing the exhalation of fluid from the skin and pulmonary membrane. While the above four essential conditions of life—the germ- force, a plasmatic material, oxygen, and caloric—are present, a healthy living organism must be the result; disease must ensue if any one of them be absent. 44 ANALYSIS OF PHYSIOLOGY. Plants and animals procure the means of their subsistence in a manner different' from each other ; the former, being fixed to the soil, cannot go in quest of the materials, but have them brought within their immediate grasp; animals, on the contrary, as soon as they commence their period of extra-uterine life (before which, they resemble plants), are forced to adopt means for procuring their supply from abroad; and for this purpose they have super- added to their organic functions a nervous system, which presides over the animal functions, or functions of relation, by means of which they obtain the power of locomotion. We may hence speak of Man as presenting two great circles, or spheres of life, totally distinct from, and independent of each other: the first, the circle of organic life, comprising the organic functions of di- gestion, absorption, respiration, secretion, and circulation; the second, the circle of animal life, including the functions of the brain (the psychological, and those of special sensation), and those of the medulla oblongata, and spinal marrow (excito- motor). The circle of organic life has for its sole object the maintenance of the " indispensable conditions of life;" thus, it is the single object of absorption to replenish the blood with a healthy plasma; digestion prepares this material for use; circulation distributes it throughout the organism; respiration introduces oxygen, and removes an effete matter—carbonic acid; secret ion either elaborates from the blood certain products, to be usefully employed in the economy, or else separates and carries off from it noxious princi- ples.—The circle of animal life places man in relationship with his fellow-man, and with the exterior world. It enables him, by the power of his intellect and the energy of his will, to subdue all surrounding nature, forcing it to become tributary to his wants, and minister to his desires. The organs of organic life are all enclosed within the trunk of the body, or are found upon the face; those of animal life are placed upon the exterior of the trunk,—as the brain, spinal marrow, spinal nerves, and muscles. The ganglionic or sympathetic nerve is a connecting link between both circles; it is placed within the ORGANIC AND ANIMAL LIFE. 45 trunk. The brain is the organ through which the mind commu- nicates with the external world. The spinal marrow presides over the reflex and automatic acts of the body; the function of its anterior columns is motor—through the nerves which proceed from its sixty-two distinct centres to the various external muscles of the body; the posterior column is excitor,—that is, it receives impres- sions made upon the nerves which take origin from its sixty-two distinct centres. By the combination of the two, excito-motor, or reflex action is produced, entirely independent of the will. As before remarked, the spinal force has frequently been con- founded with the vital force; but it is clearly only incidental to it. Moreover, it does not exist in vegetables, and the lowest order of animals breathe without it. The spinal or dynamic force is the efficient cause of locomotion; a very large amount of it is expended each day, in the ordinary movements of the body, though it is estimated that there is a saving of three-fourths in locomotion, arising from the compound nature of the levers of the foot and leg. The expenditure is rapid in proportion to the velocity employed; hence the fatigue from violent exertion. There is also a very considerable expenditure of the dynamic force in the functions of respiration, circulation, and digestion, as will be more fully explained hereafter. (Part IV.) The well-marked distinction just pointed out, as subsisting between the two great circles of life, is exhibited also in pathology. Diseases may, in fact, all be classed under the one or other circle; thus fevers, inflammations, the different cachexise, &c, may be placed in the organic circle; in these, some one of the essential conditions of life must have been interfered with. On the other hand, all the neuroses, as palsy, apoplexy, epilepsy, neuralgia, &c, must be arranged under the circle of animal life; in these the forces also have been deranged. The difference between the two is farther evidenced by the fact that an individual may retain the one set of functions in the most perfect state of health, while the other is in a condition of incurable disease; thus, a patient with complete paraplegia may have his digestion perfect, and his nutrition unimpaired, and so continue for years. PART II. OF THE MATERIALS COMPOSING LIVING ORGANIZED STRUCTURE. CHAPTER I. OF THE ELEMENTARY PARTS OF LIVING STRUCTURES. In attempting to investigate a complex mechanism like that of Man, experience demonstrates the propriety of first studying its component parts; when a thorough knowledge of these has been gained, and all their different operations understood, it will be comparatively easy to associate them together, and to study their combination of action, which constitutes the perfect machine. SECTION I. ORGANIC AND INORGANIC BODIES—ULTIMATE COMPOSITION, VARIETIES, ETC. All bodies in nature may be divided into two great classes—the inorganic and the organic. The former are governed by the laws of physics; the latter by the same laws, together with those of vitality and intelligence. The same chemical elements enter into the composition of both the above classes, with, however, this difference,—that out of the sixty-two elementary bodies at present recognised by chemists as found in the inorganic kingdom, only eighteen have ever been dis- ORGANIC AND INORGANIC BODIES. 47 covered in organic matter; hence the latter is distinguished from the former by the small number of its chemical elements. Again, these eighteen organic elements may be separated into two divisions, namely, the essential, comprising carbon, oxygen, hydrogen, and nitrogen, and so named because always found in organic matter, and the non-essential or accidental elements, con- sisting of sulphur, phosphorus, sodium, potassium, calcium, mag- nesium, manganese, iron, copper, silicon, chlorine, iodine, bromine, and fluorine. These are employed in the economy for certain specific purposes : thus lime, in combination with phosphoric and carbonic acids, gives solidity to bones; sulphur and phosphorus form a con- stituent part of albumen and fibrine; phosphorus exists in the nerve-substance, iron in the haematin of the blood, &c. The four essential elements of organic matter constitute a dis- tinct group, and from their very great importance they have re- ceived the name of radical matter. Their power of combining among each other appears almost unlimited, since it is by the simple difference in the grouping together of these four elements, with an occasional addition of one or two of the non-essential ele- ments, that the vast diversity in organized matter is produced. Thus, several distinct series of compounds of carbon and hydrogen are formed by the addition of an atom of either constituent; and by decomposing urea, its four elements may be made to assume thirty or forty new organic forms; and so of many others. Another point of difference between inorganic and organic bodies is the mode of combination of their elements. Inorganic bodies are chiefly binary, that is, are formed by the union of two dif- ferent constituent atoms; and these atoms may be either simple, as in the union of oxygen and hydrogen to form water, or of oxygen and sodium to form soda;—or they may be compound, as in the case of sulphuric acid (sulphur and oxygen) with soda (sodium and oxygen), to form sulphate of soda. Organic bodies are rarely binary; usually they are ternary, or quaternary, or even higher; thus cellulose, starch, sugar, and gum (vegetable matter) consist of carbon, oxygen, and hydrogen; while animal matter contains 48 ANALYSIS OF PHYSIOLOGY. nitrogen in addition to these, and also very often sulphur and phosphorus, as seen in proteine. As regards the mode of combination of compound bodies, there is some difference of opinion. Sulphate of soda, for example, may either be considered a compound of an acid oxide (sulphur and oxy- gen), with a basic oxide (sodium and oxygen), or one of these con- stituents may be supposed to be decomposed, yielding one of its ele- ments up to the other, which thereby forms a compound radicle^ to which the other element is suited;—thus the soda gives up its oxygen to the sulphuric acid, forming with it a compound repre- sented by S04, which is supposed to unite with the sodium. Ac- cording to this latter view, the oxy-salts would be binary, instead of ternary compounds, just as are the chlorides, iodides, &c. This view is adopted by Graham, Daniell, and others; and is of great interest when applied to the composition of organic bodies. In compound bodies, the mere addition or subtraction of a single atom will often completely change their character. An example of this is given in the different compounds of nitrogen and oxygen; also in the two chlorides of mercury. But it is even more appa- rent in organic bodies; and this will serve to explain the numerous changes which are constantly going on in living beings. The prin- ciple of isomerism may also serve to explain some of these intricate changes. Bodies are said to be isomeric when they consist of the same elements united in the same proportions, but differing very much in their properies; starch, lignin, and diastase are examples; also light-carburetted hydrogen gas and the attar of roses. Isome- rism is thought to depend upon the different arrangement of the constituent elements of a body; but it is more probable that different compound radicles are formed, which unite with a different number of simple elements, as before mentioned. The tissues of vegetables all resemble each other closely in com- position. When treated so as to separate them from the different matters which they contain, the substance remaining is termed cellulose. It is composed of carbon, oxygen, and hydrogen,—the two latter being in the proportion to form water; so that vege- table tissues may be regarded as binary compounds of carbon and ORGANIC AND INORGANIC BODIES. 49 water. Some of the vegetable products (or those proximate prin- ciples found laid up in plants) are quaternary,—containing car- bon, oxygen, hydrogen, and nitrogen, as vegetable albumen, vege- table fibrine, and vegetable caseine, which are very nearly identical with the corresponding principles of animals. The same is true also of the vegetable alkalies, as quinia, morphia, &c. There are other vegetable products which are ternary—as the oils, sugar, starch, &c. Animal tissues are quaternary, and are chiefly composed of two proximate elements—proteine and gelatine. The former of these, though of a complex nature, acts as a simple body, forming definite compounds with the different simple elements, as oxygen, sulphur, &c. The mode in which gelatine acts, is not so well known. The animal products are generally quaternary; some of them, however, are ternary, as fat, sugar of milk, &c, but there is some doubt whether these are not really produced by vegetables, and passed unaltered into the animal. Berzelius regards animal pro- ducts as binary: he supposes them to be compounds of oxygen and an organic radicle, consisting of carbon, hydrogen, and nitrogen. The combining number, or equivalent of a compound body, is high in proportion to the number of atoms which it contains; thus the equivalent of proteine is 5529, oxygen being 100. From the above distinction results also a great difference in the stability of organic and inorganic bodies. Inorganic matter con- sists of elements which are so proportioned to each other as to be completely saturated; they consequently have no tendency to sepa- rate : thus the chemical elements of water are held together by so powerful an affinity as to require considerable force to separate them; the same is true of sulphuric acid, of oxide of lead, &c. Organic matter, on the other hand, has its chemical elements more loosely held together; they are seldom completely saturated, whence it follows that their decomposition is much more easily effected; the slightest disturbing causes sufficing to produce it. This is especially true of animal matter, which, when exposed to moisture and a slight elevation of temperature, is speedily resolved into its ultimate elements, carbon, oxygen, hydrogen, and nitro- gen; and these assume the new combinations of water, carbonic 5 50 ANALYSIS OF PHYSIOLOGY. acid, ammonia, cyanogen, and, if sulphur be present, sulphuretted hydrogen. Vegetable matter is less prone to decomposition, since it contains fewer elements; thus, a piece of wood, if kept perfectly dry, will last for many years. It can now be easily understood how the molecules of organic bodies, not being in a state of equilibrium with respect to each other, are susceptible of disturbance in various ways. And as these changes are constantly occurring in the living body, they deserve special attention. 1. By a new arrangement of the molecules, without the addition or subtraction of any matter, constituting isomerism. Isomeric bodies are those which have the same chemical composi- tion, but whose properties are different. Starch, sugar, and dex- trine are examples, all having precisely similar compositions; their difference being supposed to result from the mode of arrangement of their elements. 2. By what is termed the action of presence, or catalysis. By this term is understood a change produced in the molecules of a body by the mere presence of another body not undergoing change itself. We have a familiar example in the action of spongy pla- tinum on a mixture of hydrogen and oxygen causing immediate combination and explosion. In this case it may probably be due to the condensation of the gases within the minute pores of the metal, by which they are brought down to their molecular state, and thus presented together under conditions most favourable for combination. In the same way, nitric acid is sometimes formed in the pores of old walls, by the condensation of the nitrogen and oxygen of the air; this combines, subsequently, with ammonia, and the nitrate of ammonia, thus spontaneously formed, is decomposed by potassa, so as to form saltpetre. We have numerous examples of this sort of action, both in vegetables and animals; thus the spontaneous change, in germinating seeds, of starch into dextrine and grape-sugar, through the catalytic action of diastase; a similar change is effected in starch by boiling it with dilute sulphuric acid—no change occurring, in either instance, to the catalytic body. A similar influence, it has been suggested, is exercised by the ORGANIC AND INORGANIC BODIES. 51 living cells of the body, which are thus enabled to produce those changes upon their contents resulting in the varied products of secretion and nutrition. It is the nucleus, however, rather than the cell itself, that exercises this power. 3. The.transference of action from the molecules of a body un- dergoing change, to the molecules of another body at rest, pro- ducing in it a similar change; this is termed fermentation. The presence of oxygen is always necessary to commence this process. A familiar illustration of it is exhibited in ordinary vinous fer- mentation, when the changes occurring in the yeast-cells are trans- ferred to the molecules of the sugar, the proper temperature being preserved. It is highly probable that many of the changes pro- duced in the animal fluids especially, are the result of this kind of action. For example, the digestion of albuminous food in the stomach is greatly facilitated by the pepsin of the gastric juice, which is thought to act as a ferment, converting the proteine ele- ments into what Mialhe terms albuminose,—a soluble matter capa- ble of being immediately absorbed into the blood. In the same manner contagious and malarial poisons probably produce their effects upon the system, by first contaminating the blood; the minutest quantity of variolous matter, for example, introduced into the blood, will, after a certain time, completely alter its character, so as from it to reproduce itself a thousand fold. The same thing is seen in the effects of the vaccine virus, and of the different poi- sonous animal viruses. 4. A process somewhat resembling fermentation, yet distinct from it, named by Liebig eremacausis, or slow decay. The only requisites for it are oxygen and moisture, the former being slowly absorbed. An example is afforded in the souring of wine and beer, when exposed to the air. This was formerly termed the acetous fermentation ; but it wants the true character of fermen- tation, in not requiring a ferment. Eremacausis is a process of constant occurrence in the animal economy. It is by this means, through the agency of the oxygen introduced by respiration, that the tissues are unceasingly undergoing decomposition, giving rise to numerous secondary products found in the various secretions— 52 ANALYSIS OF PHYSIOLOGY. thus urea, uric acid, carbonic acid, ammonia, phosphoric acid, &c, are formed. If this process of disintegration or decay should, at any time, exceed the reparative process,—or that by which the system is constantly built up and renewed, through the nutritive elements of food,—the result must be emaciation, and ultimately death. Instances of this are exhibited in various chronic diseases, as phthisis, &c. 5. The chemical affinity among the molecules is greatest in their nascent state, that is, while they are in the act of change or sepa- ration. Thus, arsenic and hydrogen cannot be made to combine directly by any known agency; yet they readily unite if presented to each other while in the act of escaping from some of their com- pounds,—as when an arsenical preparation is added to the materials for generating hydrogen, instantaneous combination ensues, and the very poisonous gas, arseniuretted hydrogen, results. There is every reason to believe that this condition is constantly occurring in the living organism, since we know that the various compounds existing in the blood are unceasingly undergoing change, as al- ready mentioned, and of course eliminating their elements in their nascent state, which immediately enter into new combinations. Varieties of Organic Matter.—Organic matter consists of two varieties, vegetable and animal. In most cases there can be no possible difficulty in distinguishing between these, as their marks are sufficiently characteristic. When, however, we examine the extremes of these two varieties, the strong lines of distinction gradually fade away by the investigations of the organic chemist; since cellulose, a true vegetable substance, has been discovered to exist in the structure of some of the lowest animals. The true vegetable products,—starch, dextrine, and gum,—have never been found in animal structure. Dextrine is the special organizable principle of vegetables. It is produced, as will be presently explained, by the action of dia- stase upon the starch of seeds. Dextrine constitutes the true vegetable plasma, since out of it are elaborated all the different fluids and solids of plants. As just mentioned, it does not occur in animals. ORGANIC AND INORGANIC BODIES. 53 Proteine is the basis of animal organic matter, but it is likewise found in vegetables, though always as a product arising from the combination of the elements of dextrine with those of ammonia. The most important proteine animal compounds are albumen, fibrine, and caseine ; these will hereafter be treated of at length. The proteine compounds of vegetables are named vegetable albu- men, vegetable fibrine, or gluten, and vegetable caseine, or legu- min. Neurine and gelatine, varieties of animal matter formed out of proteine, are never found in vegetables. Origin of Organic Matter.—Buffon supposed that it was origi- nally produced from its elements independently of inorganic matter; but this idea is disproved by geological researches, which exhibit the universal fact of the primitive strata never containing organic remains. The question has often been agitated whether organic matter might not be spontaneously produced by some accidental meeting together of the chemical elements, carbon, hydrogen, oxygen, and nitrogen, without the necessity for a special appa- ratus for its creation. This idea has been maintained from the circumstance that urea and alloxan, two animal matters, can be artificially produced by the chemist; and, it was urged, the same might be possibly true of all organic matter. But it is to be ob- served that neither urea nor alloxan are true organic proximate elements; they are only the products of the decomposition of organic matter, and merely its intermediate state, before it passes into its original ultimate elements. How then does organic matter originate? The living vegetable cell is the exclusive instrument of its production; the materials from which it is manufactured are water, carbonic acid, and ammonia; the agent is the sun's light. The chemist may indeed convert one organic substance into another, as starch into sugar, but he cannot out of simple inorganic matter, by the mere force of chemical affinity, no matter how powerful, create a single atom of organic matter. This wonderful transformation, is however, constantly going on in the living laboratory of the vegetable cell, which possesses the power of so acting upon the inorganic ele- 5* 54 ANALYSIS OF PHYSIOLOGY. ments of the air and soil as out of them to constitute the nume- rous vegetable products and tissues. This is accomplished in the following simple manner : The vegetable cell is composed of a double wall,—an outer one, consisting of cellulose, and an inner one, called by Von Mohl the ' primordial utricle,' an exceedingly delicate membrane, consisting of a proteine substance; these cells exist throughout the whole structure of the plant, as well in the roots as in the leaves. The arrangement in the roots consists of an extremely fine mesh of cells, termed spongiolcs, which imbibe from the soil, by endosmose, water holding in solution ammonia, some carbonic acid, and various salts of soda, potassa, lime, and silica, together with certain organic acids, of which the ulmic is the most important; these acids combining with the ammonia, tend to fix it. Most of the carbonic acid is absorbed from the air by the cells of the leaves and green portions of the plant; and in air-plants, which have no proper roots, the ammonia must be de- rived in the same manner. The next step is the decomposition of the carbonic acid and ammonia : the force concerned in the former is light, more especially the yellow ray of the solar spectrum, as proved by Prof. Draper; this force acting, deoxidizes the carbonic acid, the oxygen of which escapes into the air, whilst the carbon, in its nascent state, unites with the elements of water (or, accord- ing to Raspail, with water itself), and thus dextrine, the peculiar vegetable product is constituted. Having formed dextrine, the whole amylaceous series, com- prising starch, cellulose, gum, and sugar, may be considered as likewise produced, since these bodies are all isomeric. From these the vegetable acids are formed by the simple addition of oxygen; whilst the vegetable oils and resins are produced from the same source, by the abstraction of oxygen. The above is the first step in vegetative life-action. It consists, as will be observed, in the production of true vegetable matter, which contains no nitrogen. The next step in the process is the conversion of this into nitrogeniscd, or animal matter; and the mode of effecting this is equally simple. The dextrine within the vegetable cell forms with water a gummy solution, and thus offers ORGANIC AND INORGANIC BODIES. 55 the proper conditions for an endosmosis from the water on its out- side. This water, it will be recollected, is derived from the soil, and holds in solution a considerable quantity of ammonia. There exists in the roots a minute portion of a proteine matter, similar to the diastase of the seed, and seeming to act a catalytic part,—dis- posing the elements of dextrine to unite with the nitrogen of the ammonia. The ammonia, then, after passing into the interior of the cell, undergoes decomposition ; its nitrogen in the nascent state uniting with the dextrine to convert it into vegetable proteine matter (vegetable albumen, gluten, &c); the sulphur and phos- phorus necessary to its constitution, being derived from the earthy sulphates and phosphates taken up from the soil at the same time. By passing from cell to cell in its upward progress, the ascend- ing sap undergoes higher elaboration, forming successive new pro- ducts, as the acids, gums, resins, &c, which are deposited in diffe- rent parts of the plant. The various forces which are here in action are heat,—the importance of which has already been shown, light, endosmose, and the molecular forces. From the above consideration it is evident that vegetables are the true manufacturers of proteine, or animal matter. Animals really originate nothing. The animal cell, however, possesses the exclusive power of modifying this matter when presented to it, and causing it to assume new forms; thus, it converts common proteine into gelatine and neurine; and forms the- different tissues and organs. Vegetable matter, thus produced, becomes the appropriate food of animals. In its transit through the animal economy, it under- goes various changes through the decomposing agency of oxygen ; a portion of it being destined for the nutrition of the tissues, and a portion for furnishing the elements of combustion for the maintenance of animal temperature. Both, however, become de- composed,—first, into the various products set free by the secre- tions, as carbonic acid by the lungs, ammonia (in the form of urea) by the kidneys, water, by the skin and lungs, together with the different salts. These substances again return to their former condition in the atmosphere and soil, once more to serve 56 ANALYSIS OF PHYSIOLOGY. as the inorganic material for the constitution of other new vege- table matter. In this manner a constant circle of creation is pre- served; inorganic matter entering into the formation of vegetables; these, in their turn, constituting animal matter; and this, finally, passing back again to the original state of inorganic matter. Two inferences result from this consideration. First, that the creation of the vegetable world must have preceded that of ani- mals ; since the latter can derive their sustenance only from the former ;* secondly, that the inorganic creation was antecedent to the organic; because vegetables can only grow by the appropria- tion of inorganic materials. The above physiological discoveries are strongly confirmatory of the doctrine of an original creation of matter, and likewise of a supreme and intelligent Creator. As the inorganic series serves to form organic matters, as has been just demonstrated, so, on the other hand, organic materials often contribute to the building up of inorganic matter. Thus, it has been ascertained that many rocky strata are chiefly composed of fossil organic remains ; this is especially true of the chalk cliff of Dover. This fact has given rise to the Linnsean aphorism " omne calx e vermibus." Ehrenberg proved the same thing with respect to the silicious rocks, whence the aphorism, " omne silex e vermibus." The same thing also is to a great extent true, of some forms of iron ; the bog iron-ore being found to be gradually reproduced from animal remains, in situations from which it had been removed. Conditions of Organic Matter in Living Beings.—In living be- ings, both vegetable and animal organic matter will be found to exist under the following several different conditions, which may be considered as so many species :—1. Organizable matter, or that which is susceptible of becoming organized, or of taking on an organized form. As we have already seen, the true organizable matter of animals consists of a proteine substance—albumen; that of vegetables is dextrine. The former is capable of being con- * The infusoria may possibly form an exception to the above law, since they, like vege- tables, eliminate oxygen, in their vital processes. ORGANIC AND INORGANIC BODIES. 57 verted by life-action, into fibrine, caseine, gelatine, &c.; the latter, into the different vegetable products. 2. Organized matter, or matter which has passed out of the preceding state, and assumed a definite specific form. The vegetable kingdom affords us ex- amples of organized matter in cellulose, lignin, and cells; ani- mals furnish instances of it in corpuscles, cells, fibres, membranes, muscles, and nerves. The cause of the sp>ecicdity of form which is given to each variety of organized matter, is explicable only on the supposition that each living germ is endowed with a peculiar power of modelling the organizable material after its own type. This property of the germ has received the ap- propriate name of the modal force, or the force of modality. 3. Inorganizable matter, or matter incapable of becoming or- ganized. This is usually found as the products of the different secretions or excretions. It consists of two varieties : (a) normal —as urea, bile, milk, saliva, mucus, the spermatic fluid, &c,— found in animals; and starch, sugar, gum, oils and resins, in vegetables, (b) Abnormal—as pus, sanies, contagious matters, viruses, melanosis and tubercle, in animals;—in vegetables, ergot and galls. Many of the inorganizable products of animals are nothing more than the results of the disintegrated tissues, in their transition state to their ultimate chemical constituents;—urea is a well-marked example of this transition. The animal organizable material, or the plasma, contains within itself all the elements of the tissues and organs of the body. In its original state it is always fluid. In most animals it is elabo- rated from exterior materials by the digestive process. The mode of its supply will of course vary according to the nature and habit of the animal, but it is of the greatest importance that this supply, as regards both quantity and quality, should be adequate to the incessant requirement of the organism. This material is needed, not only for the growth of the animal, but likewise for the renewal of what is lost by the ordinary waste or disintegration of the tis- sues, in the performance of their usual functions. This loss is estimated to be about two ounces per diem, from the nitrogenized tissues. An abundant supply of this plasma is insured to every 58 ANALYSIS OF PHYSIOLOGY. living molecule of the body, through the numerous and intricate capillary retes; and the smallness of the vessels, together with the closeness of the rete, is always in proportion to the activity of function in any organ; thus, in bone and cartilage, where the function is inactive, the capillaries are large, but few in number; whilst in glands and mucous membranes, whose functions are performed with great rapidity, the rete is very close and intricate, but composed of very minute vessels. From the fact that each organ has its own specific capillary arrangement, Burdach has called the capillary system "the stereotyped expression of the organs;" and a minute corroded injection of any one of them would afford a certain evidence of the relative activity of its functions. It follows, from what has just been said, that when the function of any part of the system becomes exalted above its normal stan- dard, a greater amount of blood must flow into it from surround- ing parts, in order to afford it the requisite supply: this is illus- trated in cases of local irritation, when the parts affected always become more vascular than in health. Such a condition, con- stantly kept up, is very liable to terminate in inflammation, as is frequently witnessed in the brain of persons whose minds are in constant and intense excitement. It is of the greatest importance to pay due attention to the plasma, since it is the pabulum of the whole body. Now, as this is constituted from the nitrogenized portion of the food, it becomes of the utmost consequence that the latter should be of the proper character. But we need not pursue the subject farther, in this place, since it has already been sufficiently enlarged upon. (Part I.) States of Organic Matter.—Organic matter exists in two dif- ferent states—the solid and fluid. The concurrence of the two is indispensable to life, though the fluid must always precede the solid in the organizing process. Some consider the fluid to be the element of life, and the solid the product of life. They are most intimately associated in disease as well as in health; nor cau they be separated in therapeutics. The doctrines of the soiidists PROXIMATE CONSTITUENTS OF THE ORGANISM. 59 or humoralists prevailed according as the solids or fluids of the body were believed to be chiefly implicated in disease. The proportion between the solids and fluids varies exceedingly in-different animals. A medusa, weighing twelve pounds, will, when dried, only yield a few drachms of solid matter. The pro- portion also varies in the different tissues of the same animal; thus, in bone, cartilage,ligaments, &c, the solids predominate; in glands, mucous membranes, &c, the fluids are in excess. Even in the same organ, the proportion is not at all times the same, since the fluids always increase in congestion and inflammation. As already mentioned, the supply of blood to every organ is regu- lated by the activity of its functions; and any deviation from this will constitute disease, ^hus, when the blood is in excess, hype- raemia is the result, followed by hypertrophy and plethora; when deficient, anaemia is produced, and atrophy is a frequent conse- quence. The fluids are much more under the control of remedies than the solids; thus, bloodletting acts powerfully, both in diminishing the quantity of the circulating material, and by changing the direction of its current, especially when locally abstracted by cups and leeches. By diet, also, the plasma (fluids) may be materially modified, if not completely revolutionized, as is witnessed in the dietetic treatment of certain chronic diseases. CHAPTER II. PROXIMATE CONSTITUENTS OF THE ORGANISM. The proximate organic elements are those forms of organized matter which are the immediate result of the chemical combina- tion of the ultimate elements in the process of organization. They are sometimes spoken of as the principles which exist ready formed 60 ANALYSIS OF PHYSIOLOGY. in organic beings. Starch, gum, and sugar are examples of proxi- mate constituents in vegetables; albumen, fibrine, and gelatine are instances of the same principles in animals. The organic proximate elements may be conveniently arranged under the four following groups, or classes:—1. The proteine group; 2. The gelatine group; 3. Neurine, or nerve-substance; 4. Haematine. These principles may be regarded as the true building materials of the animal structure, since out of them are constituted all the different organs and tissues of the economy. As it is of the utmost importance that they should be properly understood by the student, in order that lie may appreciate their various modifi- cations and functions, both in the healthy and diseased structure, they will be treated of separately, and somewhat at length. SECTION I. THE PROTEINE GROUP. This class comprises the following seven proximate constituents: albumen, fibrine, caseine, pepsin or animal diastase, salivin or ptyalin, globuline, and crystalline. The name proteine was given by Mulder to a substance obtained from albumen : it is derived from the Greek tt^arsva, I take the precedence, and has reference to the important relations which it bears to the animal organism. It is procured from either albu- men, fibrine, or caseine, by dissolving in a moderately strong solu- tion of caustic potassa, digesting at 140° F., adding subacetate of lead until it ceases to blacken; then filter, and add acetic acid in excess, which throws down a white, flocculent precipitate : this is proteine; it is next to be placed upon a filter, washed, and dried. It is a whitish, flocculent substance, without taste, resembling caseine, insoluble in water, but swells up in that liquid. A dilute alkali will readily dissolve it, but acids precipitate it from its solution. Its composition, as originally determined by Mulder, PROTEINE. 61 is C4oH31N5012; according to Liebig, C^BJUfi^+one equivalent of sulphur. In repeating Mulder's experiments for obtaining proteine, Liebig found that it always contained sulphur and phosphorus, and he was hence disposed to deny its existence altogether. Subsequently, Mulder himself has admitted the correctness of Liebig's views, and has so modified his formula for proteine, as to make it embrace both phosphorus and sulphur. There are two methods of interpreting the production of this remarkable substance. It may be that it pre-exists in the natural albuminous principles, which, on that supposition, must be viewed as compounds of proteine, with sulphur and phosphorus, or with sulphur only : or it may be regarded as merely a product of the action of the alkalies on these bodies, the sulphur and phosphorus being at the same time separated. Proteine exists both in vegetables and animals; in the former as a product, in the latter as a part of the structure. Animals always derive it ready formed from vegetables. The seeds of plants, and the tissues of animals present it in the solid form; the leaves and roots of plants, and the animal fluids exhibit it in the liquid form. In plants or animals, it is readily converted from a liquid into a solid, by meeting with an acid. In this manner we can account for its deposit in the cells of plants, and also for the formation of certain morbid products in the animal economy. An alkali, on the other hand, will dissolve solid proteine; and, in this way, the efficacy of the alkaline treatment, in certain forms of disease, can be explained. Proteine enters into numerous combinations: with oxygen it unites in several proportions, forming the binoxide of proteine, C40H31NsO14, and tritoxide of proteine, C40H31N5O13. The former of these is in- soluble ; the latter is soluble. They are both supposed to exist in definite quantities in healthy blood, being formed in the process of respiration. In inflammation they accumulate, and constitute the chief ingredients of the buffy coat, being produced at the ex- pense of the fibrine. The principle found in pus, named pyine, is 6 62 ANALYSIS OF PHYSIOLOGY. believed to be a protoxide of proteine. A still higher oxidation constitutes pepsin and ptyalin ; and Mulder asserts the existence of an oxy-proteine, in which the oxygen is in the proportion of twenty parts. With sulphur and phosphorus proteine forms a number of very important compounds; in fact, these are the only combinations in which proteine naturally exists in either vegetables or animals. The following is a list of some of these proteine-compounds:— Albumen of serum, .... pr+Sa+P. Albumen of eggs, ----- Pr+S+P. Fibrine, .... - Pr+S+P. Caseine, ------ Pr+S. Crystalline, ----- Pr+S. Similar compounds to the above are found in vegetables, and are named respectively, vegetable albumen, vegetable fibrine, or gluten, and vegetable caseine, or legumin. These all contain nitro- gen, and are regarded by Mulder as identical in composition with the animal proteine elements; Liebig, however, does not admit their complete identity. The precise mode of combination be- tween proteine and sulphur and phosphorus is not well understood; but it is believed that the two latter exist as amides, constituting sulph-amide and phosph-amide. Besides *the above proteine- compounds there are numerous others, of a similar character, whose exact composition is not yet known, such as hair, horns, nails, &c. Proteine also unites with acids and alkalies : with the former as a base, with the latter as an acid, forming a soluble proteate. With sulphuric acid it forms sulpho-proteic acid; with nitric acid, xantho-proteic acid. 1. Albumen.—C^H^N-O^+P+S^—This principle is found in the white and yellow of eggs, in the serum of blood, in the humours of the eye, in serous exudations, in the urine under cer- tain diseased conditions, and in various morbid products, as tubercle, &c. As found in the egg, and in the serum of the blood, it differs THE PROTEINE GROUP—ALBUMEN. 63 slightly in composition; the former (ov-albumen) containing one equivalent less of sulphur than the latter (ser-albumen). In vege- tables it exists in the seeds and juices; some plants, as the cab- bage, consist almost exclusively of this principle combined with gluten, with little or no starchy matter; for this reason it is well adapted as an article of diet in diabetes mellitus, a disorder in which there is a tendency to convert all non-azotized food into sugar. Albumen exists in two states, the fluid and solid. When per- fectly pure, it is always solid; and its natural solubility in the serum of the blood, and in other albuminous fluids, is owing to the presence of a little free soda, and the salts of soda and lime. When precipitated in its pure state, it is nearly colourless, in- odorous, and tasteless. Its characteristic property is its coagulation by heat. The temperature required for this purpose varies with the state of dilution. If the solution be so strong as to have a slimy aspect, a heat of 150° to 160° F. will suffice; but if very dilute, a boiling temperature will be required. Coagulated albu- men presents no traces of organization. It is solid, white, and opaque; it dries up into a yellow horny substance, which, when macerated in water, assumes its former whiteness and opacity. When coagulated at a very low temperature, it will re-dissolve in water. The only chemical change which occurs during the act of coagulation by heat is the removal of the alkali and the soluble salts by the hot water. Coagulated albumen exposed to a mode- rate temperature and moisture, soon undergoes putrefaction, de- veloping animalcules; but if slightly acidulated, this does not occur; a copious, mould-like vegetation taking its place. Albu- men is likewise coagulated by tannin, alcohol, creasote, and electricity; when acted upon by electricity, the albumen appears at both poles,—at the positive pole, in union with hydrochloric acid, and at the negative, in union with soda. According to Chevreul, ether and oil of turpentine coagulate the albumen of eggs, but not that of serum. Albumen, unites with acids as a base, and with alkalies as an acid. 3Iost of the acids in excess will precipitate it from its 64 ANALYSIS OF PHYSIOLOGY. solution, forming compounds with it; but the acetic, tribasic (common) phosphoric, lactic, and tartaric acids dissolve it in all proportions. The gastric juice of the stomach owes its acidity to the presence of some of these latter acids; and it is doubtless to them that its solvent power over the albuminous elements of food is due. United with the alkaline earths in small proportion, al- bumen is soluble; with a large proportion it is insoluble. It forms insoluble compounds with the salts of the metallic oxides, but the albumen is divided between the base and the acid; hence its value as an antidote in cases of poisoning from corrosive sublimate, or the salts of copper. The chemical relations of albumen are interesting in a thera- peutical view. Thus, in cases where the acetate of lead is em- ployed as a collyrium in inflammation of the eye, if there is an open ulcer of the cornea, the lead would unite with the exposed albumen of the tissue, and form an insoluble compound, which would result in a permanent opacity of the cornea. The insoluble compounds of albumen and the metallic oxides become again soluble when they meet with the alkaline chlorides in the alimen- tary canal; hence, in cases where albumen has been given as the antidote, it should be accompanied by a cathartic to remove the resulting compound from the bowels as soon as possible. The different degree of solubility of certain poisonous substances, when united with albumen, will explain very satisfactorily the difference in their poisonous effects; for example, the cyanide of mercury produces an almost immediate effect, because it forms a soluble compound with the albumen of the stomach, and is consequently readily absorbed into the blood; whilst corrosive sublimate, under the same circumstances, forms an insoluble compound, which requires the subsequent action of the alkaline chlorides before it can be re-dissolved, and enter the circulation. For the same reason, nitric acid does not act as a poison so promptly as oxalic acid, though a far more powerful acid than the latter, because it forms an insoluble compound with the albumen. The proportion of albumen in the serum of the blood is just that which is sufficient to enable it to dissolve the phosphate of lime, THE PROTEINE GROUP—FIBRINE. 65 and thus to furnish the material for the construction of bones. The best tests for albumen are its coagulability by heat and nitric acid; also one recommended by Prof. Rogers,—a dilute solution of sulphate of copper added to liquor potassae; a purple colour is produced. There are likewise other tests of inferior value. Cor- rosive sublimate, as already mentioned, will immediately precipi- tate albumen : four grains of it will neutralize the white of one egg- Albumen, as such, does not enter into the construction of any healthy tissue of the body; it is rather the point of departure at which the organizing process commences. It is the crude material furnished by the nitrogenized food, and destined to undergo the various transformations in the vital processes. 2. Fibrine.—C^ Hal N5 0^+8+P.—Isomeric with albumen, and is generally regarded as produced from it by the process of organization. Dumas supposes it to be an oxidized albumen. M. Banard's opinion is that much of the albuminose, resulting from the digestive process, is transformed at once into fibrine, as it passes through the liver. His ground for this notion is that the portal blood contains most of the digested azotized matter, and but little fibrine, even when the animal had been fed upon meat; whereas the blood of the hepatic veins contains much fibrine, and but little albuminose; and further, that this difference is only observed during digestion. The only method of distinguishing liquid fibrine from albumen is by the spontaneous coagulation of the former, which .is its characteristic test. Fibrine is found in the animal body in two forms; as a solid, in muscular flesh, and as a liquid, in blood, lymph, and occasionally in dropsical effusions, and in urine in disease. It exists likewise in the gluten of the cereal plants, and in the juices of certain vegetables. It is best procured from blood, either by washing the coagulum until all the soluble parts are removed, or by agitating it as it flows from a vessel, with a bundle of twigs, to which it will adhere, then washing it in cold water, and removing the fat by ether. When thus procured, it is in the form of long, white, elastic filaments, which, under the microscope, appear to be cmn- 6* 66 ANALYSIS OF PHYSIOLOGY. posed of small globules, arranged in strings; it is tasteless, and insoluble in water, either hot or cold. By long boiling it is par- tially dissolved. When dried at a gentle heat, it loses about 80 per cent, of water, and is converted into a translucent horny sub- stance, resembling coagulated albumen. It dissolves completely in a dilute solution of a caustic alkali, and the solution much resembles that of albumen. Phosphoric acid produces a similar effect. Nitric acid converts it into xantho-proteic acid. It is soluble in a dilute alkali. It is readily converted into albumen by the process of digestion; and like albumen, it acts both as an acid and a base. It also unites with the earthy phosphates. In the act of coagulating, fibrine assumes a peculiar fibrillary arrangement, very much after the manner of crystallization; as is witnessed particularly in the buffy coat of inflammation. But the most perfect specimens of fibrous structure, produced by simple coagulation of fibrine, are found in the exudations from inflamed or wounded surfaces, constituting false membranes ; also in the fibrous coating which the ovum receives as it passes along the oviduct, which afterwards becomes the shell. The completeness of the production of such tissues depends, partly upon the degree of elaboration of the fibrine, and partly upon the nature of the sur- face on which the coagulation takes place. This is believed by many to be the first step in the organizing process; and it is very possible that some of the primitive fibres of the body may be in this manner formed, without the intervention of cells. The tendency of fibrine to undergo spontaneous coagulation has already been noticed: to this cause alone is due the disposition of the blood to coagulate, as is proved by the experiment of filtering a frog's blood,—the liquid portion which passes through alone coagulates, the corpuscles remaining on the filter. The same thing is also shown in the process of procuring fibrine by whipping freshly- drawn blood with a bundle of twigs. The degree of firmness of the coagulum depends upon the amount of fibrine present. The normal proportion of fibrine in blood is from 2-5 to 3 parts in a thousand. The reason why the blood does not coagulate in the living body is probably because the contact with a living surface THE PROTEINE GROUP—FIBRINE. 67 keeps it within the influence of vitality, or, as suggested by Dumas (who believes the fibrine of the blood to be always in a state of minute division, and not of solution), because it is passing out of the circulation for the supply of the various organs, as rapidly as it is elaborated. Fibrine was at one time supposed to be the immediate plasma, or material for the construction of the organism ; but the discovery of the oxy-proteines renders it probable that it is only in the transit tion state. The accumulation of fibrine in inflammation is to be considered rather as an increase of the oxides of proteine, as already pointed out, when treating of proteine. Blood deficient in fibrine,— as seen in certain low forms of fever, retains its dark venous hue when exposed to the influence of oxygen. The above is the commonly-received doctrine upon the origin and destination of fibrine in the animal economy. The recent views of Dr. Simon (Gen. Pathol.) are strongly opposed to it. From numerous observations made by himself and others, he found that the proportion of fibrine in the blood very decidedly increased in diseases essentially ansemic, during violent fatigue, and the like, in some cases even beyond what was found in inflammation. In one case of experimental starvation of a horse, he found, after four days' total abstinence, that the proportion of fibrine had risen from five to nine parts in the thousand. It is also well known that bleeding does not diminish the amount of fibrine, but, on the con- t trary, rather appears to augment it; this is confirmed by both Andral and Scherer. It is just the reverse with respect to the red corpuscles, which are uniformly diminished by bleeding and starvation, or exhausting diseases. From the above facts Simon questions the theory that fibrine is essential to the progressive de- velopment of the tissues, but regards it rather as an excrementi- tious product, derived from the waste of the tissues, or oxidation of the blood, and in progress of elimination from the system. On this view, any increase in the proportion of fibrine must be regarded only as an indication of increased labour and waste in certain ele- ments of the body, not of an increased development in the resources and nutrition of the blood; and the super-fibrination of the blood 63 ANALYSIS OF PHYSIOLOGY. in inflammatory diseases would be considered rather as their con- sequence than as their cause. The fibrine of arterial and venous blood is not absolutely iden- tical; the latter when treated with one-third of its weight of nitrate of potassa and water, at the temperature of 100°-120° F., is converted into a solution in all respects identical with albumen. With arterial fibrine no such liquefaction ensues; and even venous fibrine loses this property when long exposed to the air or oxygen gas. The fibrine of muscular flesh resembles venous fibrine. A peculiar point of distinction between albumen and fibrine is the effect of the latter upon deutoxide of hydrogen,—causing its instantaneous decomposition. 3. Caseine.—CJH^N.jO^+S. This is the coagulable portion of milk, and the basis of cheese. Milk, as shown by Prout, con- tains all the different forms of aliment within itself; the albu- minous are represented by caseine, the saccharine or amylaceous by lactine or sugar of milk, and the oily by butter. It also contains several alkaline and earthy matters. Caseine exists in minute quantities in the blood, bile, urine, pus, and crystalline lens (Simon); never in any of the solids in health, but only as a morbid product, as in tubercle. It closely resembles albumen, and may easily be mistaken for it; like that substance it is insoluble when pure, and owes its solubility to the fc presence of a small quantity of alkali. It differs from albumen in not coagulating by heat, and in being precipitated by acetic acid, which dissolves pure albumen. Another distinction is that it contains no phosphorus. Unlike albumen and fibrine, caseine does not combine with acids, though with bases it plays the part of a feeble acid. It is easily convertible into albumen and fibrine, as seen in the digestive and nutritive processes of young animals. The spontaneous coagulation of milk, when allowed to rest for a time, is due to a species of fermentation by which the sugar of milk is converted into lactic acid through the agency of the caseine; this acid then neutralizes the alkali of the milk, and consequently precipitates the caseine in its natural solid form. Two equivalents of lactic acid, 2 (CcIIBOfi) are yielded by every single equivalent of THE TROTEINE GROUP--PEFSINE. 69 sugar of milk (C^H^OJ. Any acid will in this manner produce coagulation in milk; but the effect of rennet, or the inner coat of a calf's stomach, in causing this change is remarkable,—a piece of rennet coagulating 1800 times its own weight of milk. This power of the mucous membrane is, by some, attributed to the acid of its gastric juice ; but the same effect is produced even when the acid is neutralized by an alkali; it is doubtless owing to the pepsine contained in the membrane of the stomach, which has been shown by Berzelius to be capable of coagulating 45,000 times its weight of milk. Liebig supposes the pepsine to act merely as a ferment, converting the sugar into lactic acid; and Simon has proved that if milk be deprived of its sugar, the pepsine fails to produce coagu- lation. Fresh milk contains no lactic acid, but is, on the con- trary, feebly alkaline. Human milk retains its alkaline character longer than any other kind. Milk will be treated of more at large under the head of Secre- tion. 4. Pepsine, or Gasterase.—This organic principle was so named by Eberle, from