4' \' ■'■ 4* A. f-t» *%, r^; ARMY MEDICAL LIBRARY FOUNDED 1836 WASHINGTON, D.C DEC 3 1958 /(Z- PHYSIOLOGY OF DIGESTION CONSIDERED WITH RELATION TO THE PRINCIPLES OF DIETETICS. BY ANDREW COMBE, M.D. FELLOW OF THE ROYAL COLLEGE OP PHYSICIANS OF EDINBURGH : PHYSICIAN EXTRAORDINARY TO THE if we were required to point out any single year of the whole century during which a marked reformation took place, we should not be able to do so. This being the case, then, can we, their descendants, maintain that we are arrived so nearly at perfection as to leave no room for corresponding improvement in our day, however slow it may also be ? My conviction is so much the reverse, that it seems to me certain that our onward progress will continue through generationa yet unborn, with the same steadiness as it has done through generations long since gathered to their fathers; and that every attempt made to render man better acquainted with the laws of his own constitution, and thereby provide him with fixed and better principles of action, will exert a positive and decided influence on the progress of the race, proportioned in extent to the truth, clearness, and general applicability of the views which are unfolded. On such considerations do I ground my hope that the present volume, notwithstanding its nume- rous defects, will (in so far as it really imbodies truths of practical importance) contribute in its own limited sphere to the general end. The real cause of the little regard paid to dietetic rules— and it is of consequence to remark it—is not so much indiffe- rence to their influence, or even the absolute want of valuable information, as the faulty manner in which the subject is usual- ly considered. In many of our best works the relation subsist- ing between the human body on the one hand, and the qualities of dimentary substances on the other, is altogether lost sight of, although it is the only solid principle on which their proper adaptation to each other can be based. In this manner, while the attention is carefully directed to the consideration of the abstract qualities of the different kinds of aliment, little or no regard is paid to the relation in which they stand to the indi- vidual constitution, as modified by age, sex, season, and cir- cumstances, or to the observance of the fundamental laws of digestion. And hence, although these conditions are not un- frequently of much greater importance to the general health than even the right selection of food, yet, when indigestion arises from neglecting them, the food alone is blamed, and erroneous conclusions aro drawn, by relying on which, upon future occasions, we may easily be led into still more serious mistakes. It is, indeed, from being left in this way without any guid- ing principle to direct their experience,, and test the accuracy of the precepts laid down to them for the regulation of their conduct, that many persons begin by being bewildered by the numerous discrepancies which they met with between facts end doctrine, between counsel and experience-*and end by becoming entirely skeptical on the subject of all dietetic rules I* ti PREFACE. whatever, and regarding them as mere theoretical effusion*, based on fancy, and undeserving of a moment's consideration. The true remedy for this state of things is, not to turn away in disgust and despair, but to resort to a more rational mode of inquiry—certain that, in proportion as we advance, some useful result will reward our labours. Such, accordingly, has been my aim in the present publication , and if I shall be found to have been even moderately successful in attaining it, I shall rejoice in the confident conviction that others will be led to still more positive and beneficial results. Utility has been my great object throughout. In following what I conceive to be an improved mode of investigation, I have in some instances placed known facts in a new point of view, and deduced from them practical inferences of considerable value and easy ap- plication : but beyond this I am not ambitious of originality ; and if I have anywhere used expressions which may seem to do injustice to others, it has been entirely without any such design, and, consequently, I will be prompt to acknowledge my error and rectify the involuntary mistake. In the previous editions of this volume I stated that I had derived the utmost advantage from a very valuable work by Dr. Beaumont, an American writer, which—though faulty in its arrangement, and necessarily defective in many essential particulars—contains an authentic record of some of the most curious and instructive observations which have ever been made on the process of digestion. That excellent and en- lightened physiologist had the rare good fortune to meet with a case where an artificial opening into ths stomach existed, through which he could see everything that took place during the progress of healthy digestion ; and, with the most disin- terested zeal and admirable perseverance, he proceeded to avail himself of the opportunity thus afforded of advancing human knowledge, by engaging the patient, at a heavy expense, to live with him for several years, and become the subject of numerous and carefully conducted experiments. Having, through the kindness of a friend resident in the United States, been early favoured with a copy of the original work, I felt so strong a conviction of the superior value of investigations con- ducted under circumstances so unusually free from the many sources of fallacy inseparable from experiments on animals, that at the time I had almost resolved to reprint it entire, both as an act of justice to Dr. Beaumont, and as a valuable con- tribution to physiological science. In the belief, however, that a republication would immediately appear from some other quarter, I abstained from doing so, and contented myself with making free use of such parts of it as seemed most calculated. to throw light upon the practical questions which 1 was en- gaged in discussing. But after waiting in vain for two years. PRBFACK. Tli and finding the interest excited in Dr. Beaumont's experiments increased in proportion as their nature and value became more extensively known by means of the extracts given in the pre- sent volume, I felt it due to Dr. Beaumont to delay no longer, and accordingly republished his work with the addition of various explanatory and practical notes,* and the high favour with which it has been welcomed by the leading medical jour- nals shows that I did not exaggerate its importance. Dr.'Beaumont's work being thus rendered accessible tc the English reader, 1 was anxious, in the present edition, to omit as much of the matter formerly extracted from it as I possibly could. But, on making the attempt, I found the extracts ever) - where so mixed up with the practical conclusions which they were used to enforce, that I could not leave them out without materially weakening the argument. I have, therefore, retain- ed them; and an additional reason for doing so was, that Dr. Beaumont's volume is in the hands almost exclusively of pro- fessional men, and is thus likely to remain almost as little known to the general reader as if it were still confined in circulation to the other side of the Atlantic. Objections may be stated to several of the repetitions which occur in the following pages. The only apology 1 have to offer for them is, that I committed them deliberately, because they seemed to me necessary to ensure clearness, and because the intimate manner in which the different functions are connected with each other sometimes made it impossible to explain one without again referring to the rest. My prime objects being to render the meaning unequivocally plain, and impress the subject deeply upon the reader's mind, I thought it better to risk in this way the occasional repetition of an important truth, than to leave it in danger of being vaguely apprehended or its true value unperceived. For these reasons, it is hoped that the fault—if such it is—will be leniejitly overlooked. * Experiments and Observations on the Gastric Juice and the rtivsiology of Digestion, by William Beaimont, M.D., of the United States Army. Reprinted with Notes by Andrew Combe, M.D 1 vol. post 8vo Edinburgh, 1833 ADVERTISEMENT TO THE THIRD EDITION. The first edition of the present volume consisted of two thousand copies, and was exhausted in little more than five months. The second extended to the very unusual number of four thousand copies, and has now been for some weeks out of print. In the United States the work has also been twice republished. This success is very gratifying, and affords a very encouraging indication that the importance of physiolo- gical knowledge as a branch of general instruction is every day becoming better understood and more extensively recognised. In the edition now in the hands of the reader various im- provements have been effected. Of these the most important has been the introduction of a new chapter, explaining more fully the relation subsisting between the different kinds of food and the principal varieties of the human constitution. Several other improvements, of a still more extensive kind, had also occurred to me, but long-continued indisposition has prevented me from carrying them into effect. In this uncer- tainty, it seemed to me better rather to reprint the work with such alterations as I was able to make on it, than to defer its appearance for an indefinite time ; and I trust that most of my readers will concur in thinking that in this I have decided correctly. With these apologetic remarks, I must now leave the work, with all its remaining imperfections, to the kind indulgence of the public. Edinburgh, 25 Rutland-itreet, Octobtr 15,1641. CONTENTS. PART I. PHYSIOLOGY OF DIGESTION. CHAPTER I. GENERAL VIEW OF THE OBJECTS AND LAWS OF NUTRITION. Waste or loss of substance always attendant on action—In the ve- getable and animal kingdoms waste is greater than in the phy- sical—Living bodies are distinguished by possessing the power of repairing waste—Vegetables, being rooted in one place, are always in connexion with their food—Animals, being obliged to wander, receive their food at intervals into a stomach—Nutrition most active when growth and waste are greatest—In vegetables the same causes which increase these processes also stimulate nutrition—But animals require a monitor to warn them when food is needed—The sense of Appetite answers this purpose— The possession of a stomach implies a sense of Appetite to regu- late the supplies of food. 25-31 CHAPTER II. THE APPETITES OF HUNGER AND THIRST. Hunger and Thirst, what they are—Generally referred to the stomach and throat, but perceived by the brain—Proofs and illus- trations—Exciting causes of hunger—Common theories unsatia factor}'—Hunger sympathetic of the state of the body as well as of the stomach—Uses of appetite—Relation between waste and appetite—Us practical importance—Consequences of overlooking it illustrated by analogy of the whole animal kingdom—Disease C-om acting in opposition to this relation—Effect of exercise oa appetite explained—Diseased appetite—Thirst—Seat of Thirst— Circumstances in which it is most felt—Extraordinary effects of injection of water into the veins in cholera—Uses of thirst, and rules for gratifying it. 31-51 CHAPTER III. MASTICATION, 1NSALIVAT10N, AND DEGLUTITION. Mastication—The teeth—Teeth, being adapted to the kind of food, vary at different ages and in different animals—Teeth classed and described—Vitality of teeth, and its advantages—Causes of disease in teeth—Means of protection—Insalivation, and its uses —Gratification of taste in mastication—Deglutition. 51-63 CHAPTER IV. ORGANS OF DIGESTION—THE STOMACH--THE GASTRIC JUICE. Surprising power of digestion—Variety of sources of food—AH structures, however different, fbrmed from the same blood—Ge- neral view of digestion, chymification, chylification, sanguifica- tion, nutrition—The stomach in polypes, in quadrupeds, and in man—Its position, size, and complexity in different animals—Its structure ; its peritoneal, muscular, and villous coats ; and uses of each—Its nerves and bloodvessels ; their nature, origins, and uses—The former the medium of communication between the brain and stomach—Their relation to undigested food—Animals X CONTESTS. not conscious of what goes on in the stomach—Advantages of this arrangement—The gastric juice the grand agent in digestion— Its origin and nature—Singular case of gunshot wound making a permanent opening into the stomach—Instructive experiments made by Dr. Beaumont—Important results. 63-99 CHAPTER V. ;*f THEORY AND LAWS OF DIGESTION. Different theories of Digestion—Concoction—Fermentation—Putre* faction—Trituration—Chemical solution—Conditions or laws of digestion—Influence of gastric juice—Experiments illustrative of its solvent power—Its mode of action on different kinds of aliment; beef, milk, eggs, soups, &c.—Influence of temperature—Heat of about 100° essential to digestion—Gentle and continued agitation necessary—Action of stomach in admitting food—Uses of its muscular motion—Gastric juice acts not only on the surface of the mass, but on every particle which it touches—Digestibility of different kinds of food—Table of results—Animal food most dr. gestible—Farinaceous next—Vegetables and soups least digestible —Organs of digestion simple in proportion to concentration of nutriment—Digestibility depends on adaptation of food to gastric juice more than an analogy of composition—Illustrations—No increase of temperature during digestion—Dr. Beaumont's sum- mary of inferences. 99-129 CHAPTER VI. CHYLIFICATION, AND THE ORGANS CONCERNED IN IT. Chylification—Not well known—Organs concerned in it—The intestinal canal—Its general structure—Peritoneal coat—Mesen- tery—Muscular coat—Uses of these—Air in intestines—Uses of —Mucous coat—Analogous to skin—The seat of excretion and absorption—Mucous glands—Absorbent vessels—Course of chyle toward the heart—Nerves of mucous coat—Action of bowels ex- plained—Individual structure of intestines—The duodenum; jeju- num ; and ileum—Liver and pancreas concerned in chylification —Their situation and uses—Bile, its origin and uses—The pan- creas—Its juice—The jejunum described—The ileum ; coecum ; colon ; and rectum—Peristaltic motion of bowels—Aids to it- Digestion of vegetables begins in stomach, but often finished in the bowels—Illustration from the horse—Confirmation by Dupuy- tren. 129-152 PART II. THE PRINCIPLES OF DIETETICS VIEWED IN RELATION TO THE LAWS OF DIGESTION. CHAPTER I. TIMES OF EATING. The selection of food only one element in sound digestion—O Lac conditions essential— Times of eating—No stated hours for eat- ing—Five or six hoars of interval between meals generally sufli- C0HTKNT9. Xi dent; but must vary according to circumstances—Habit has much influence—Proper time for breakfast depends on constitu- tion, health, and mode of life—Interval required between break- fast and dinner; best time for dinner ; circumstances in which lunch is proper ; late dinners considered ; their propriety depen- dant on mode of life—Tea and coffee as a third meal; useful in certain circumstances—Supper considered—-General rule as to meals—Nature admits of variety ; illustrations j but requires the observance of principle in our rules. 153-175 CHAPTER II. ON THE PROPER QUANTITY OF FOOD. Quantity to be proportioned to the wants of the system—Appetite indicates these—Cautions in trusting to appetite—General error in eating too much—Illustrations from Beaumont, Caldwell, Head, and Abercrombie—Mixtures of food hurtful chiefly as tempting to excess in quantity—Examples of disease from_ excess in servant-girls from the country, dressmakers, &c.—Mischief from excessive feeding in infancy—Rules for preventing this— Remarks on the consequences of excess in grown persons- Causes of confined bowels explained—And necessity of fulfilling the laws which God has appointed for the regulation of the animal economy inculcated. 175-196 CHAPTER III. CONDITIONS TO BE OBSERVED BEFORE AND AFTER RATING. General laws of organic activity apply to the stomach as well as to other parts—Increased flow of blood toward the stomach during digestion—Hence less circulating in other organs—And, con- «equently, less aptitude for exertion in them—Bodily rest and mental tranquillity essential to sound digestion—Rest always attended to before feeding horses—Hence also a natural aversion to exertion immediately after eating—Mischief done by hurry- ing away to business after meals—Severe thinking hurtful at that time—Playful cheerfulness after dinner conducive to di- gestion—The mind often the cause of indigestion—Its mode of operation explained—Also influences nutrition—Illustration from Shakspeare—Importance of attending to this condition of health enforced. 197-207 CHAPTER IV. THE DIFFERENT KINDS OF CONSTITUTION AND OF FOOD CONSIDERED WITH RELATION TO EACH OTHER. Man remarkable for the variety of his food ; advantages of this — Man not guided by instinct to the choice of his food, but by ob- servation and experience ; his welfare thus intrusted to himself —Principle on which fitness of food ought to be determined ; in- formation still much wanted—Nature of constitution to be con- sidered—Varieties of constitution or temperament; the lymphatic, nervous, sanguine, bilious, and mixed temperaments—Diet ought to be modified according to temperament; illustrations—Different kinds of food ; their classification and division into animal and regetable—Londe's propositions regarding their relative digesti- iiUty—Animal food and its varieties; its chemical composition no Ill CONTENTS. test ot its dietetic qualities—Division into fibrinous, gelatinous, and nrouminous meats—Adaptation of each of these to different temperaments, ages, and states of health—Vegetable aliments and their properties ; principal divisions of them, and general remarks on their use and adaptation. 206-231 CHAPTER V. ADAPTATION OF DIET TO CONSTITUTION, AGS, SEASON, AND MODE OF LIFE. food to be adapted to constitution and circumstances—Diet must vary with time of life—Diet in infancy—The mother's milk the best j substitutes for it—Over-feeding a prevalent error—Diet after weaning—Too early use of animal food hurtful—Diet of children in the higher classes too exciting ; and produces scro- fula—Mild food best for children—Incessant eating very inju- rious—Proper diet from childhood to puberty—It ought to be full and nourishing, but not stimulating ; often insufficient in board- ing-schools—Diet best adapted for mature age—Regimen powerful in modifying the constitution, mental as well as physical—Far. mer investigation required. 231-249 CHAPTER VI. ON DRINKS. Wairst the best guide in taking simple drinks—Thirst increased by diminution of the circulating fluids—The desire for liquids gene- rally an indication of their propriety—Much fluid hurtful at meals—Most useful three or four hours later—The temperature of drinks is of consequence—Curious fall of temperature in the stomach from cold water—Ices hurtful after dinner—Useful in warm weather, when digestion is completed and caution used— Cold water more dangerous than ice when the body is overheat- ed—Tepid drinks safest and most refreshing after perspiration__ Kinds of drink—Water safe for every constitution—Wine, spirits, and other fermented liquors too stimulating for general use, but beneficial in certain circumstances—Test of their utility. 250-263 CHAPTER VII. ON THE PROPER REGULATION OF THE BOWELg. Functions of the intestines—The action of the bowels bears a na- tural relation to the kind of diet—Illustrations—And also to the other excretions—Practical conclusions from this—Different causes of inactivity of bowels—Natural aids to intestinal action —General neglect of them—Great importance of regularity of bowels—Bad health from their neglect—Especially at the age of puberty—Natural means preferable to purgatives—Concluding remarks. 264-276 Index. 277-287 WOODCUTS. Under-jaw, 52.—Thoracic and Abdominal Viscera, 68.—Human Stomach, 69.—Stomach of a ruminating animal, 71.__Villous Coat of the Stomach, 75.—Opening into the Stomach of Alexis St. Mar- tin, 86.—Abdominal Viscera, 132.—Transverse section of the Abdo- men, 133.—Lacteals and Thoracic Duct, 138.—Thoracic Duct, 139. —Contents of the Abdomen after removal of the Intestines 143 — Mucous Coat of the Duodenum, 145. PART I. PHYSIOLOGY OF DIGESTION. CHAPTER I. QENERAL VIEW OF THE OBJECTS AND LAWS OF NUTRITION. Waste or loss of substance always attendant on action—In the ve- getable and animal kingdoms waste is greater than in the phy- sical—Living bodies are distinguished by possessing the power of repairing waste—Vegetables, being rooted in one place, are always in connexion with their food—Animals, being obliged to wander, receive their food at intervals into a stomach—Nutrition most active when growth and waste are greatest—In vegetables the same causes which increase these processes also stimulate nutrition—But animals require a monitor to warn them when food is needed—The sense of Appetite answers this purpose— The possession of a stomach implies a sense of Appetite to regu- late the supplies of food. Throughout every department of Nature waste is the invariable result of action. Even the minutest change in the relative position of inanimate objects cannot be effected without some loss of substance. So well is this under- stood, that it is an important aim in mechanics to discover the best means of reducing to the lowest possible degree the waste consequent upon motion. Entirely to prevent it is admitted to be beyond the power of man ; for however nicely parts may be adjusted to each other, however hard and durable their materials, and however smoothly motion may go on, still in the course of time loss of substance becomes evident, and repair and renewal become indis- pensable to the continuance of the action. It is thus a recognised fact, or general law of nature, that nothing can act or move without undergoing some change, however trifling in amount. Not even a breath of wind can pass along the surface of the earth without altering in some degree the proportions of the bodies with which it comes into contact; and not a drop of rain can fall upon a stone without carrying away some portion of its substance. The smoothest and most accurately formed wheel, running along the most level and polished railroad, parts with some poition of its substance at every revolution, and in process of time is worn out and requires to be replaced. The same effect is forcibly, though rather ludicrously, exemplified in the great toe of the bronze statue of St. Peter at Rome, which in the course of centuries has been worn down to less than half its original size by the successive kisses of the faithful; and I venture to mention it, because it affords one of the best specimens of the operation of a principle, 26 waste always attendant on action. the existence of which, from the imperceptibly small effect of any single act, might otherwise be plausibly denied. As regards dead or inanimate matter, the destructive influence of action is constantly forced upon our attention by everything passing around ns; and so much human ingenuity is exercised to counteract its effects, that no re- flecting person will dispute the universality of its operation. But when we observe shrubs and trees waving in the wind, and animals undergoing violent exertion, for year after year, and yet both continuing to increase in size, we may be inclined, on a superficial view, to regard living bodies as constituting exceptions to the rule. On more careful ex- amination, however, it will appear that waste goes on in living bodies not only without any intermission, but with a rapidity immeasurably beyond that which occurs in inani- mate objects. In the vegetable world, for instance, every leaf of a tree is incessantly pouring out some portion of its fluids, and every flower forming its own fruit and seed, speedily to be separated from, and lost to, its parent stem ; thus causing in a few months an extent of waste many hundred times greater than what occurs in the same lapse of time after the tree is cut down, and all its living opera- tions are at a close. The same thing holds true in the animal kingdom. So long as life continues, a copious ex- halation from the skin, the lungs, the bowels, and the kid- neys goes on without a moment's intermission ; and not a movement can be performed which does not at least partially increase the velocity of the circulatbn, and add something to the general waste. In this way, during violent exertion several ounces of the fluids of the body are sometimes thrown out by perspiration in a very few minutes ; where- as, after life is extinguished, all the excretions cease, and waste is limited to that which results from ordinary chemical decomposition. So far, then, the law that waste is attendant on action, applies to both dead and living bodies; but beyond this point a remarkable difference between them presents itself. In the physical or inanimate world, what is once lost 01 worn away is lost for ever. There is no power inherent in the piston of the steam-engine by which it can repair its own loss of particles ; and consequently in the course of time it must either be laid aside as useless, or be remo- delled by the hand of the workman. But living bodies, nhethsr vegetable or animal, possess the distinguishing LIVING BODIES CAN REPAIR THEIR WASTE. 27 characteristic of being able to repair their own waste and add to their own substance. The possession of such a power is, in fact, essential to their very existence. If the sunflower, which in fine weather exhales thirty ounces of fluid between sunrise and sunset, contained no provision within its own structure for replacing this enormous waste, it would necessarily shrivel and die within a few hours, as it actually does when plucked up by the roots; and, in like manner, if man, whose system throws out every day five or 6ix pounds of substance by the ordinary channels of excre- tion, possessed no means of repairing the loss, his organi- zation would speedily decay and perish. This very result is frequently witnessed in cases of shipwreck and other disasters, where, owing to the impossibility of obtaining food, death ensues from the body wasting away till it be- comes incapable of carrying on the operations of life. In some instances this waste has even proceeded so far that three-fourths of the whole weight of the body have been lost before life became extinct. It is impossible to reflect on these facts, and others of a similar kind, without having the conviction forced upon our minds, that in every department of nature expenditure of material is inseparable from action, and that in living bodies waste goes on so rapidly, and by so many different channels, that life could not be maintained for any length of time without an express provision being made for com- pensating its occurrence. In surveying the respective modes of existence of vege- tables and of animals, with the view of ascertaining by what means this compensation is effected, the first striking dif- ference between them which we perceive, is the fixity of position of the one, and the free locomotive power of the other. The vegetable grows, flourishes, and dies, fixed to the same spot of earth from which it sprang; and, however much external circumstances may change around it, it must remain and submit to their influence. If it be deprived of moisture and solar heat and light, it cannot go in search of them, but must remain to droop and to perish. If the earth to which its roots are attached be removed, and a richer soil be substituted than that which its nature requires, it etill has no option : it must grow up in rank and unhealthy luxuriance, in obedience to an impulse which it cannot re- sist. At all hours and at all seasons it is at homo, and in direct communication with the soil from which its nourish- 38 ANIA'ALS RECEIVE FOOD AT INTERVALS. ment is extracted. And being thus without ceasing in rontact with its food, it requires no store-house in which to lay up provision, but receives immediately from the earth, and at every moment, all that is necessary for its sustenance. But it is otherwise with animals. These not only enjoy the privilege of locomotion, but are compelled to use it, and often to go to a distance, in search of food and shelter. Consequently, if their vessels of nutrition were, like those of vegetables, in direct communication with external sub- stances, they would be torn asunder at every movement, and the animals themselves exposed either to die from star- vation, or to forego the exercise of the higher functions for which their nature is adapted. But the necessity for a constant change of place being imposed on them, a diffe- rent arrangement became indispensable for their nutrition: and the method by which the Creator has remedied the incon- venience is not less admirable than simple. To enable the animal to move about, and at the same time to maintain a con- nexion with its food, He has provided it with a receptacle or stomach, where it is able to store up a supply of mate- rials from which sustenance may be gradually elaborated during a period of time proportioned to its necessities and mode of life. It thus carries along with it nourishment adequate to its wants ; and the small nutritive vessels im- bibe their food from the internal surface of the stomach and bowels, where the nutriment is stored up, just as the roots or nutritive vessels of vegetables do from the soil in which they grow. The possession of a stomach or receptacle for food is accordingly a characteristic of the animal system as contrasted with that of vegetables ; it is found even in the lowest orders of zoophytes, which in other respects are so nearly allied to plants. The sole objects of nutrition being to repair waste and to admit of growth, Nature has so arranged that within certain limits it is always most vigorous when growth or waste proceeds with the greatest rapidity. Even in vege- tables this relation is distinctly observable. In spring and summer, when vegetative life is most active, and when leaves, flowers, and fruit are to be formed and growth car- ried on, nourishment is largely drawn from the soil, and the elaboration and circulation of the sap are proportionally vigorous; whereas in winter, when the leaves and flowers have passed away, and vegetable life is in repose, little nourishment is needed, and the circulation of the sap ia RELATION BETWEEN WASTE AND NUTRITION. 29 proportionally slow. In accordance with these facts, every one will recollect how freely a shrub or a tree bleeds, as it is called, when its bark is cut early in the season, and how dry it becomes on the approach of winter. It is the activity of the circulation in summer which renders its temporary suspension by transplanting so generally fatal at that season; whereas, owing to the comparative sluggishness with which it is carried on in winter, its partial interruption is then at- tended with much less risk. In vegetables the quantity of nourishment taken in en- tirely depends on, and is regulated by, the circumstances in which they are placed. When they are exposed, as in spring and summer, to the stimulus of heat and light, all their functions are excited, waste and growth are acce- lerated, and a more abundant supply of nourishment be- comes indispensable to their health and existence; and hence, in a dry soil incapable of affording a copious sup- ply of sap, they speedily wither and die. Exposed to cold, on the other hand, and shaded from the light, their vitality is impaired, and the demand for nourishment greatly di- minished. This is uniformly the case in winter; and many circumstances show that the change is really owing to the causes mentioned above, and not to anything inherent in the constitutionof the vegetable itself. In tropical climates, for example, where heat, light, and moisture abound, ve- getable life is ever active, and the foliage ever thick and abundant; and even in our own northern region we are able, by artificial heat, so far to anticipate the natural order of the seasons, as to obtain the ripened fruit of the vine in the very beginning of spring. The whole system of forcing vegetables and fruit, so generally resorted to for the early supply of our markets, is, in truth, founded on the princi- ple we are now discussing ; and, by the regulated applica- tion of heat, light, and moisture, we are able to hasten or to retard, to a very considerable extent, the ordinary stages of vegetable life. But to ensure success in our operations, we must be careful to proportion the supply of nourishment to the state of the plant at the time. II, by the application of heat, we have stimulated it to premature growth and foliage, we must at the same time provide for it an ade- quate supply of food, otherwise its activity will exhaust itself, and induce permature decay. Hence the regular watering which green-house plants require. But if we have 30 ANALOG? OF VEGETABLES AND ANIMALS. retarded its progress and lowered its vitality by excluding heat and light, the same copious nourishment will not only be unnecessary, but will probably do harm by inducing re- pletion and disease. In vegetables the absorption of food is thus regulated chiefly by the circumstances of heat, moisture, and light under which the plant is placed, and by the consequent necessity which exists at the time for a larger or smaller supply of nourishment to carry on the various processes of vegetable life. According to this arrangement, nutrition is always most active when the greatest expenditure of ma- terial is taking place. When growth is going on rapidly, and the leaves are unfolding themselves, sap is sucked up from the earth in immense quantity ; but when these pro- cesses are completed as summer advances, and almost no fresh materials are required, except for the consolidation of the new growth and the supply of the loss by exhalation, a much smaller amount of nourishment suffices, and the sap no longer circulates in the same profusion. In autumn, again—when the fruit arrives at maturity, the leaves begin to drop off, and the activity of vegetable life suffers abate- ment—nutrition is reduced to its lowest ebb ; and in this state it continues till the return of spring stimulates every organ to new action, and once more excites a demand for an increased supply. Nor is the same great principle, of supply requiring to be proportioned to demand, less strikingly apparent in animals. Wherever growth is proceeding rapidly, or the animal is undergoing much exertion and expenditure of material, an increased quantity of food is invariably required ; and, on the other hand, where no new substance is forming, and where, from bodily inactivity, little loss is sustained, a com- paratively small supply will suffice. But as animals are subjected to much more rapid and violent transitions from activity to inactivity than vegetables are—and thus require to pass more immediately from one kind and quantity of nourishment to another, in order to adapt their nutrition to the ever-varying demands made upon the system—they evidently stand in need of some provision to enforce atten- tion when nourishment is necessary, and to enable them always to proportion the supply to the real wants of the body. Not being, like vegetables, in constant connexion with their aliment, they might suffer from neglect if they did not possess some contrivance to warn them in Uma THE APPETITES OF HUNOER AND THIRST. 81 when to seek and in what quantity to consume it. But is endowing animals with the sense of Appetite, or the sen- sations of Hunger and Thirst generally included under it, the Creator has guarded effectually against the inconve- nience, and given to them a guide in every way suflicienl for the purpose. The very possession of a stomach or receptacle, into which food sufficient for a shorter or longer period can bd introduced at one time, and which we have already remark ed as characterizing all animals from the lowest to the highest, almost necessarily implies the coexistence of some watchful monitor, such as appetite, to enforce attention to the wants of the system, with an earnestness which it shall not be easy to resist. If this were not the case in man, for example—if he had no motive more imperative than reason to oblige him to take food—he would be constantly liable, from indolence and thoughtlessness, or the pressure of other occupations, to incur the penalty of starvation, without being previously aware of his danger. But the Creator, with that beneficence which distinguishes all His works, has not only provided an effectual safeguard in the sensations of hunger and thirst, but, moreover, attached to their regulated indulgence a degree of pleasure which never fails to insure attention to their demands, and which, in highly civilized communities, is apt to lead to excessive gratification. Such being the important charge committed to the appetites of hunger and thirst, it will be proper to submit to the reader, before entering upon the consideration of the more complicated process of digestion, a few remarks on their nature and uses. CHAPTER II. THE APPETITES OF HUNOER AND THIRST. Hunger and Thirst, what they are—Generally referred to the stomach and throat, but perceived by the brain—Proofs and illus- trations—Exciting causes of hunger- Common theories unsatis- factory—Hunger sympathetic of the state of the body as well as of the stomach—Uses of appetite—Relation between waste and appetite—Its practical importance—Consequences of overlooking it illustrated by analogy of the whole animal kingdom—Disease from acting in opposition to this relation—Effect of exercise on appetite explained—Diseased appetite—Thirst—Seat of Thirst— Circumstances in which it is most felt—Extraordinary effects oi injection of water into the veins in cholera—Uses of thirst, and rules for gratifying it. In the preceding chapter I endeavoured to shovf,ji~stf 32 BEAT OF THE SENSATION OF HUNOER. that nutrition is required only because waste and a deposi- tion of new particles are continually going on, so that the body would speedily become exhausted if its constituent materials were not renewed ; secondly, that the sense of appetite is given to animals for the express purpose of warning them when a fresh supply of aliment is needed— as, without some such monitor, they would be apt to neglect the demands of nature; and thirdly, that vegetables have no corresponding sensation, simply because, from their being at all times in communication with the soil, their nutrition goes on continuously in proportion as it is neces- sary, and without requiring any prompter to put it in action at particular times. If these principles be correct, it follows that, in the healthy state, (and let the reader be once for all made aware that in the following pages the state of health is always inplied, except where it is otherwise plainly expressed,) the dictates of appetite will not be every day the same, but will vary according to the mode of life and wants of the system, and, when fairly consulted, will be sufficient to direct us both at what time and in what quantity we ought to take in either solid or liquid sustenance. But to make this perfectly evident, a few general observations may be required. It is needless to waste words in attempting to describe what hunger and thirst are : every one has felt them, and no one could understand them without such experience, any more than sweetness or sourness could be understood without tasting sweet or sour objects. Their end is mani- festly to proclaim that farther nourishment is required for the support of the system ; and our first business is, there- fore, to explain their nature and seat, in so far at least as a knowledge of these may be conducive to our welfare. The sensation of hunger is commonly referred to the stomach, and that of thirst to the upper part of the throat and back of the mouth ; and correctly enough to this extent, that a certain condition of the stomach and throat tends to produce them. But, in reality, the sensations themselves, like all other mental affections and emotions, have their seat in the brain, to which a sense of the condition of the stomach is conveyed through the medium of the nerves. In this respect Appetite resembles the senses of Seeing, Hearing, and Feeling ; and no greater difficulty attends the explanation of the one than of the others. Thus, the cause which excites the sensation of colour is certain rays of light HUNGER A MENTAL SENSATION. 33 striking upon the nerve of the eye ; and the cause which excites the perception of sound is the atmospherical vibra- tions striking upon the nerve of the ear ; but the sensations themselves take place in the brain, to which, as the organ of the mind, the respective impressions are conveyed. In like manner, the cause which excites appetite is an impres- sion made on the nerves of the stomach ; but the feeling itself is experienced in the brain, to which that impression is conveyed. Accordingly, just as in health no sound is ever heard except when the external vibrating atmosphere has actually impressed the ear, and no colour is perceived unless an object be presented to the eye—so is appetite never felt, except where, from want of food, the stomach is in that state which forms the proper stimulus to its nerves, and where the communication between it and the brain is left free and unobstructed. But as, in certain morbid states of the brain and nerves- voices and sounds are heard, or colours and objects are seen, when no external cause is present to act upon the ear or the eye—so, in disease, a craving is often felt when no real want of food exists, and where, consequently, indul- gence in eating can be productive of nothing but mischief. Such an aberration is common in nervous and mental dis- eases, and not unfrequently adds greatly to their severity and obstinacy. In indolent unemployed persons, who spend their days in meditating on their own feelings, this craving is very common, and, from being regarded and indulged as if it were healthy appetite, is productive of many dys- peptic affections.* If the correctness of the preceding explanation oi the sensation of hunger be thought to stand in need of confir- mation, I would refer to the very conclusive experiments by Brrchet, of Lyons, as setting the question entirely at rest. Brachet starved a dog for twenty-four hours, till it became ravenously hungry, after which he divided the nerves which convey to the brain a sense of the conditioa of the stomach. He then placed food within its reach, but the animal, which a moment before was impatient to be fed, went and lay quietly down, as if hunger had never been experienced. When meat was brought close to it, it began to eat; and, apparently from having no longer any con- • Dyspepsia (from the Greek words due, dus, bad, and nenru, pepto, I concoct) is synonymous with indigestion. 84 NERVOUS COMMUNICATION BETWEEN THE sciousness of the state of its stomach—whether it was full or empty—it continued to eat till both it and the gullet were inordinately distended. In this, however, the dog was evidently impelled solely by the gratification of the tense of taste ; for, on removing the food at the beginning of the experiment to tho distance of even a few inches, it looked on with indifference, and made no attempt either to follow the dish or to prevent its removal.* Precisely similar results eusued when the nervous sym- pathy between the stomach and brain was arrested by the administration of narcotics. A dog suffering from hunger turned listlessly from its food when a few grains of opium were introduced into its stomach. It may be said that such a result is owing to the drug being absorbed and carried to the brain through the ordinary medium of the circulation; but Brachet has proved that this is not the case, and that the influence is primarily exerted upon the nerves. To establish this point, two dogs of the same size were selected. In one the nerves of communication were left untouched, and in the other they were divided. Six gains of opium were then given to each at the same mo- ment. The sound dog began immediately to feel the effects of the opium and became stupid, while the other continued lying at the fire-side for a long time, without any unusual appearance, except a little difficulty of breathing. In like manner, when the experiment was repeated with that powerful poison mix vomica, upon two dogs similarly circumstanced, the sound one fell instantly into convul- sions, while the other continued for a long time as if no- thing had happened. These results demonstrate, beyond the possibility of doubt, the necessity of a free nervous communication be- tween the stomach and brain, for enabling us to experience the sensation of hunger. The connexion between the two organs is, indeed, more widely recognised in practice than it is in theory; for it is a very common custom with the Turks to use opium for abating the pangs of hunger when food is not to be had, and sailors habitually use tobacco for the same purpose. Both substances act exclusively on the nervous system. The relation thus shown to subsist between the stomach * Brachet, Recherche* Experimentales sur les Fonctions du Systems Nerveux Ganglionaire, chap. iii. Paris edition. STOMACH AND BRAIN NECESSARY FOR IT8 PERCEPTION. 35 and the brain, enables us in some measure to understand the influence which strong mental emotions and earnest intellectual occupation exert over the appetite. A man in perfect health, sitting down to table with an excellent ap- petite, receives a letter announcing an unexpected calamity, end instantly turns away with loathing from the food which, a moment before, he was prepared to eat with relish; while another, who, under the fear of some misfortune, comes to table indifferent about food, will eat with great zest on his " mind being relieved," as the phrase goes, by the receipt nf pleasing intelligence. Excessive and absorbing emotion, even of a joyful kind, has the same effect. Captain Back tells us, in the interesting narrative of his last journey, that when he first heard of Captain Ross's return, " the thought of so wonderful a preservation overpowered, for a time, the common occurrences of life. We had but just sat down to breakfast, but our appetite was gone, and the day passed in a feverish state of excitement." (P. 245.) In such cases no one will imagine that the external cause destroys ap- petite otherwise than through the medium of the brain. Occasionally, indeed, the aversion to food amounts to a feeling of loathing and disgust, and even induces sickness and vomiting—a result which depends so entirely on the state of the brain, that it is often excited by mechanical injuries of that organ. The analogy between the external senses and the appe- tite is in various respects very close. If we are wrapped in study, or intent on any scheme, we become insensible to impressions made on the ear or eye. A clock may strike, or a person enter the room, without our being aware of either event. The same is the case with the desire for food. If the mind is deeply engaged, the wants of the system are unperceived and unattended to—as was well exemplified in the instance of Sir Isaac Newton, who, from seeing the bones of a chicken lying before him, fancied that he had already dined, whereas, in reality, he had eaten nothing for many hours. Herodotus ascribes so much effi- cacy to mental occupation in deadening the sense of hun- ger, that he speaks of the inhabitants of Lydia having successfully had recourse to gaming as a partial substitute for food, during a famine of many years continuance. In this account there is, of course, gross exaggeration; but it illustrates sufficiently well the principle under discussion. 36 CAUSE OF THE SENSATION OF HUNOER. Many attempts have been made, but without much suc- cess, to determine what the peculiar condition of the stomach is which excites in the mind the sensation of hunger. For a long time it was imagined that the pre- sence of gastric or stomach juice, irritating the nerves of the mucous membrane, was the exciting cause ; but it was at last ascertained that, after the digestion of a meal is completed, and the chyme has passed into the intestine, the gastric juice ceases to be secreted till after a fresh supply of food has been taken in.* It was next supposed that the mere emptiness of the stomach was sufficient to excite hunger, and that the sensation arose partly from the opposite sides rubbing against each other. But this theory is equally untenable ; for the stomach generally contains a sufficient quantity of air to prevent the actual contact of its sides, and, moreover, it may be entirely void of food, and yet no appetite be felt. It may be laid down, indeed, as a ge- neral rule, that an interval of rest must follow the termina- tion of digestion before the stomach becomes fit to resume its functions, or appetite is experienced in any degree of intensity ; and the length of time required for this purpose varies very much, according to the mode of life and to the extent of waste going on in the system. In many diseases, too, the stomach remains empty for days in succession, without any corresponding excitation of hunger. Even in healthy sedentary people, whose expenditure of bodily sub- stance is small, real appetite is not felt till long after the stomach is empty, and hence one of their most common complaints is the want of appetite. Dr. Beaumont suggests a distended state of the vessels which secrete the gastric juice as the exciting cause of hunger, and thinks that this view is strengthened by the rapidity with which the juice is poured out after a short fast—a rapidity, he says, which cannot be accounted for except by supposing the juice to have existed ready made 'n the vessels or follicles by which it is secreted. But this * It is difficult, as in the above sentence, to avoid occasionally using expressions and referring to processes which have not pre- viously been explained ; but it would only lead to confusion and unnecessary repetition to stop at every page and introduce explana- tions, which, after all, the reader would scarcely understand on ac- count of their brevity. In the present instance, therefore, where I allude to the process of digestion, it is better to refer the reader to the outline given at the beginning of Chanter IV., than to distract his 9" -*-on by introducing it also here. SYMPATHY BETWEEN SYSTEM AND 8T0MACH. 37 fteory is not more satisfactory than the rest, for in the sudden flow of saliva into the mouth of a hungry man on the unexpected appearance of savoury viands, we have an instance of equally rapid secretion where there was evi- dently no storing up beforehand. Besides, there is an olfious relation between appetite and the wants of "-he system, which is not always taken sufficiently into account, and which is, nevertheless, too important to be overlooked. If the body-be very actively exercised, and a good deal of waste be effected by perspiration and exhalation from the lungs, the appetite becomes keener, and more urgent for immediate gratification; and if it is indulged, we eat with a relish unknown on other occasions, and afterward experience a sensation of bien-etre or internal comfort per- vading the frame, as if every individual part of the body were imbued with a feeling of contentment and satisfaction, the very opposite of the restless discomfort and depression which come upon us, and extend over the whole system, when appetite is disappointed. An amusing example of the principle here inculcated is to be found in the Corres- pondence Inedite de Madame du Deffand,* where she de- scribes her friend Madame de Pequigni as an insatiable, bustling little woman who consumes two hours every day in devouring her dinner, and "eats like a wolf." But, then, remarks Madame du Deffand, by way of explanation, "iZ est vrai qu'elle fait un exercice enrage." There is, in short, an obvious and active sympathy be- tween the condition and bearing of the stomach and those of every part of the animal frame—in virtue of which, hunger is felt very keenly when the general system stands in urgent need of repair, and very moderately when no waste has been suffered. This principle is strikingly illus- trated during recovery from a severe illness. " In conva- lescence from an acute disease," as is well remarked by Brachet, "the stomach digests vigorously, and yet the in- dividual is always hungry. This happens because all the wasted organs and tissues demand the means of repair, and demand them from the stomach, which has the charge of sending them ; and, therefore, they keep up in it the con- tinual sensation of want, which, however, is, in this case, •uly sympathetic of the state of the body."t In alluding * Vol. iii., p. 40. Paris, 1909. t Brachet, Recherches Experimentalee sur let Fonctions da 8ys £me Nerveux Ganglion aire, p. 181. 38 RELATION BETWEEN WAST* *ND APPETITE. to this subject, Blaine observes, that "Hunger and thirst can only be satisfactorily explained by considering them as properties in the stomach by which it sympathizes with the wants of the constitution ; and hence it is that food taken in invigorates, even before it can be digested."* Hence also the prostration of strength that is felt when the stomach has been for some time empty. i This sympathy is sometimes singularly manifest even in disease. In some cases of affection of the mesenteric glands, for example, where stomachic digestion remains for a time pretty healthy, and the general system suffers chiefly ftom the want of nourishment caused by the passage of the chyle into the blood being obstructed, the appetite continues as keen and often keener than before ; because the system, being in want of nourishment, and the stomach healthy, all its natural causes continue to act as before ; and accord- ingly, when food is taken, it is digested there as usual, but the chyle which is formed from it in the intestine can no longer be transmitted through the swollen glands in its usual healthy manner, to be converted into nutritive blood in the lungs ; and the system thus failing to receive the required supply, recommences its cravings almost as soon as if no food had been obtained. When the disease has advanced a certain length, however, fever springs up, and destroys both appetite and digestion. The effects of exercise also show very clearly the con nexion between appetite and the state of the system. If we merely saunter out for a given time every day, without being actively enough engaged to quicken the circulation and induce increased exhalation from the skin and lungs, we come in with scarcely any change of feeling or condi- tion ; whereas, if we exert ourselves sufficiently to give a general impetus to the circulation, and bring out moderate perspiration, but without inducing fatigue, we feel a light- ness and energy of a very pleasurable description, and ge- nerally accompanied by a strong desire for food. Hence the keen relish with which the fox-hunter sits down to table after a successful chase. This intimate communion between the state of the sys- tem and that of the stomach is a beautiful provision of Nature, and is one of the causes of the ready sympathy which has often been remarked as existing between the 'Blaine's Outlines of the Veterinary Art, third edition, p. 378 RELATION BETWEEN WASTE AND APPETITE. 39 stomach and all the other organs—in other words, of the readiness with which they accompany it in its departure from health, and the corresponding aptitude of their disor- ders to produce derangement of the digestive function. Ap- parently for the purpose, among others, of thus intimately connecting the stomaoh with the rest of the system, it is supplied with a profusion of nervous filaments of every kind, which form a closely-interwoven nervous network in its immediate neighbourhood, and the abundance of which accounts for the severe and often suddenly fatal result of a heavy blow on the pit of the stomach. Without pretending to determine what the precise con- dition of the nerves of the stomach is, which, when con- veyed to the brain, excites the sensation of appetite, I think it sufficient for every practical purpose if we keep in mind, that the co-operation of the nervous system is ne- cessary for the production of appetite, and that there is a direct sympathy between the stomach and the rest of the body, by means of which the stimulus of hunger becomes unusually-urgent where the bodily waste has been great, although a comparatively short time has elapsed since the preceding meal. Appetite, then, being given for the express purpose of warning us when a supply of food is necessary, it follows that its call will be experienced in the highest intensity when waste and growth—or, in other words, the operations which demand supplies of fresh materials—are most ac- tive ; and in the lowest intensity when, from indolence anc» the cessation of growth, the demand is least. In youth, accordingly, when bodily activity is very great, and a libe- ral supply of nourishment is required both to repair waste and to carry on growth, the appetite is keener and less discriminating than at any other period of life, and, what is worthy of remark, as another admirable instance of adap- tation, digestion is proportionally vigorous and rapid, and abstinence is borne with great difficulty ; whereas, in ma- ture age, when growth is finished and the mode of life more edentary, the same abundance of aliment is no longer needed, the appetite becomes less keen and more select in its choice, and digestion loses something of the resistless power which generally distinguishes it in early youth. Articles of food which were once digested with ease, are now burdensome to the stomach, and, if not altogether re- 40 EVILS FROM NEGLECTING THE RELATION jected, are disposed of with a degree of labour and diffi- culty that was formerly unknown. Abstinence also is now more easily supported. When, however, the mode of life in mature age is ac- tive and laborious, and the waste matter thrown out of the system is consequently considerable, the appetite for food and the power of digesting it are correspondingly strong ; for in general it is only when the mode of life is indolent and inactive, and the waste consequently small, that the appetite and digestion are weak. So natural, indeed, is the connexion between the two conditions, that exercise is proverbially the first thing we think of recommending to improve the appetite and the tone of the digestive organs, when these are observed to be impaired ; and where po- sitive disease does not exist, no other remedy is half so effectual. But, as already noticed, exercise to be benefi- cial must be of a description calculated to increase the activity of the secretions and excretions; otherwise it cannot place the system in a condition to require an abun- dant supply or excite vigorous digestion. It is highly important to notice this natural relation between waste and appetite, and between appetite and di- gestion ; because, if it be real, appetite must be the safest guide we can follow in determining when and how much we ought to eat. It is true that in disease, and amid the factitious calls and wants of civilized life, its suggestions are often perverted, and that hence we may err in blindly following everything which assumes its semblance. The conclusion to be drawn from this, however, is, not that the sense of hunger will, if trusted to, generally mislead us, but only that we must learn to distinguish its true dic- tates before we can implicitly rely on its guidance. If, when fairly consulted, its dictates are found to be erro- neous, it will constitute the only known instance where the Creator has failed in the attempt to fulfil his own de- sign—an assumption not only repugnant alike to feeling and to reason, but, in fact, altogether gratuitous. For the apparent discrepancies which occasionally present them- selves between the wants of the system and the dictates of appetite, are easily explicable on the more solid ground cf our own ignorance and inattention. Many practical errors arise from overlooking the rela. 1MB which nutrition ought to bear to waste and growth. BETWEEN WASTE AND APPETITE. 41 Thus, it is no uncommon thing for young men who have experienced all the pleasures of a keen appetite and easy digestion when growing rapidly or leading an active life, to induce severe and protracted indigestion, by continuing, from mere habit, to eat an equal quantity of food either when growth is finished and the system no longer requires the same extensive supply, or after a complete change from active to sedentary habits has greatly diminished that waste which alone renders food necessary. This is, in fact, one of the chief sources of the troublesome dyspeptic complaints often met with among the youthful inhabitants of our larger cities and colleges, and ought not to be lost sight of in the physical education of the young. The error, however, is unhappily not confined to the young, but extends generally to all whose pursuits are of a sedentary nature. There are numerous persons, especially \n towns and among females, who, having their time and employments entirely at their own disposal, carefully avoid everything which requires an effort of mind or body, and pass their lives in a state of inaction entirely incompatible with the healthy performance of the various animal func- tions. Having no bodily exertion to excite waste, promote circulation, or stimulate nutrition, they experience little keenness of appetite, have weak powers of digestion, and require but a limited supply of food. If, while inactive and expending little, such persons could be contented to follow nature so far as not to provoke appetite by stimulants and rookery, and to eat and drink only in proportion to the wants of the system, they would fare comparatively well. But having no imperative occupation and no enjoyment from active and useful exertion, their time hangs heavily on their hands, and they are apt to have recourse to eating as the only avenue to pleasure still open to them; and, forgetful or ignorant of the relation subsisting between waste and nutrition, they endeavour to renew, in the present indul- gence of appetite, the real enjoyment which its legitimate gratification afforded under different circumstances. Pur- suing the pleasures of the table with the same ardour as Before, they eat and drink freely and abundantly, and, instead of trying to acquire a healthy desire for food and Increased powers of digestion by exercise, they resort to j)nics, spices, wine, and other stimuli, which certainly excite 1st the moment, but eventually aggravate the mischief by 4* 42 EVILS FROM NEGLECTING THE RELATION, ETC. obscuring its progress and extent. The natural result of this mode of proceeding is, that the stomach becomes op- pressed by excess of exertion—healthy appetite gives way, and morbid craving takes its place—sickness, headache, and bilious attacks become frequent—the bowels are habitually disordered, the feet cold, and the circulation irregular—and a state of bodily weakness and mental irritability is induced, which constitutes a heavy penalty for the previous indul- gence. So far, however, is the true cause of all these phenomena from being perceived even then, that a cure is sought, not in a better regulated diet and regimen, but from bitters to strengthen the stomach, laxatives to carry off the redundant materials from the system, wine to overcome the sense of sinking, and heavy lunches to satisfy the mor- bid craving which they only silence for a little. Some, of course, suffer in a greater and others in a less degree, ac- cording to peculiarities of constitution, mode of life, and extent of indulgence; but daily experience will testify that, in its main features, the foregoing description is not over- charged, and that victims to such dietetic errors are to be met with in every class of society. The fact of Nature having meant the inactive and indo- lent to eat and drink less than the busy and laborious, is established not only by the diminished appetite and impair- ed digestion of human beings who lead a sedentary life, as contrasted with the keen relish and rapid digestion usually attendant on active exertion in the open air, but on a yet broader scale by the analogy of all other animals. In no- ticing this relation, Dr. Roget remarks, that " the greater the energy with which the more peculiarly animal functions of sensation and muscular action are exercised, the greater must be the demand for nourishment, in order to supply the expenditure of vital force created by these exertions. Com- pared with the torpid and sluggish reptile, the active and vivacious bird or quadruped requires and consumes a much larger quantity of nutriment. The tortoise, the turtle, the toad, the frog, and the chameleon will, indeed, live for months without taking any food." " The rapidity of de- velopement," he continues, " has also great influence on the quantity of food which an animal requires. Thus the caterpillar, which grows very quickly, and must repeatedly throw off its integuments, during its continuance in the ferva state, consumes a vast quantity of food compared with FULL DIET INCOMPATIBLE WITH INACTION. 49 the size of its body ; and hence we find it provided with a digestive apparatus of considerable size."* Hence, too, the greater demand for food in infancy and youth when growth and activity are both at their height. In thus insisting on regular bodily and mental activity as indispensable to the enjoyment of a good appetite and sound digestion, the attentive reader will not, I trust, be disposed to accuse me of inconsistency because, when treating of muscular exercise in the former volume,11 explained the bad effects, and inculcated the impropriety, of indulging in any considerable exertion immediately before or after a full meal. It is true, as there mentioned, that exercise, either in excess or at an improper time, impairs the tone of the stomach; but it is not on that account the less true that bodily exertion, when seasonably and properly practised, is the best promoter of appetite and digestion which we pos- sess ; and it is only under the latter conditions that I now speak of it as beneficial and even indispensable to health. In a work like the present, it is obviously impossible to fence round every general proposition with the numerous limitations which an unusual combination of circumstances, or a departure from the state of health, might demand. And, even if possible, it would not be necessary, as the laws of exercise have been so fully explained in the volume alluded to, that their rediscussion here would unavoidably involve much repetition from its pages. At the same time, some warning remark may be required to prevent any risk of misconception, as it might otherwise be plausibly argued, for example, that there can be no such relation as T have alleged between waste and appetite, because a European perspiring under a tropical sun incurs great waste, and yet loses both appetite and digestive power. To render this a valid exception, it must be shown that the European is in- tended by Nature to live in a tropical climate, and that the diet to which he accustoms himself is that sanctioned by experience as the best adapted for his constitution ; be- cause, if neither is the case, his condition under such influ- ences must necessarily be more or less closely allied to the state of disease, and therefore beyond the sphere to which alone my remarks are meant to apply. But even in that in- stance there is less contradiction than might be imagined, • Roget's Bridgewater Treatise on Animal and Vegetable Phy- tfology, vol. ii., p. 112. f Principles of Physiology, fcc., chapters IV. and V. 44 FULL DIET INCOMPATIBLE WITH INACTION. for the waste of the system, being chiefly fluid, excites— tot appetite, but its kindred sensation—thirst, to repair the loss by an unusual demand for refreshing liquids. So true is it that the Creator has established a relation letween action and nutrition, that when we attempt for any length of time to combine a full and nutritious diet with systematic inactivity, the derangement of health which generally ensues gives ample proof of the futility of strug- gling against His laws. Individuals, indeed, may be met with, who, from some peculiarity of constitution, suffer less than the generality of mankind from making the ex- periment ; but even those among them who escape best, generally owe their safety to the constant use of medicine, or to a natural excess in some of the excretory functions, such as perspiration or the urinary or alvine discharges, by means of which the system is relieved much in the same way as by active exercise ; and hence the remark made by Hippocrates, that severe perspirations arising during sleep without any other apparent cause, are a sure sign that too much nourishment is made use of. In others, again, the day of reckoning is merely delayed, and there is habitually present a state of repletion, which clogs the bodily func- tions, and may lead to sudden death by some acute disease wher the individual is apparently in the highest health. I am acquainted with several individuals of this description, who, in the absence of all bodily exercise, are accustomed to live very fully—to eat in the morning a hearty breakfast, with eggs, fish, or flesh—a good solid luncheon, with wine or malt liquor, in the forenoon—a most substantial dinner, with dessert and several glasses of wine, and afterward tea and wine and water, in the evening—and who, nevertheless, enjoy tolerably good digestion. But this advantage is gene- rally only temporary, and even when permanent can scarcely be considered as a boon ; because it is gained at the direct expense either of a very full habit of body and an unusual liability to abdominal congestion and all its attendant evils, or of frequent and profuse perspirations, and severe attacks of bowel complaint, endangering life ; so that, strictly con- sidered, such cases are no exceptions to the general rule. It is, then, no idle whim of the physician to insist on Ictive exercise as the best promoter of appetite and di- gestion. Exercise is, in fact, the condition without which ^halation and excretion cannot go on sufficiently fast to DEFICIENT DIET AND EXCESS OF LABOUR. 45 tlear the system of materials previously taken in; and where no waste is incurred, no need of a fresh supply, and, conse- quently, in a healthy state of the system, no natural appetite, can exist. It is, therefore, not less unreasonable than vain 'or any one to insist on possessing, at the same time, the incompatible enjoyments of luxurious indolence and a vigo- rous appetite—sound digestion of a hearty meal, and general health of body ; and no one who is aware of the relation subsisting between waste and appetite, can fail to perceive the fact, and to wonder at the contrary notion having ever keen entertained. Among the operative part of the community we meet with innumerable examples of an opposite condition of the system, where, from excess of labour, a greater expenditure •f energy and substance takes place than what their defi- cient diet is able to repair. It is true that the disproportion Is generally not sufficient to cause that immediate wasting which accompanies actual starvation, but its effects are, aevertheless, very palpably manifest in the depressed buoy- ancy, early old age, and shorter lives of the labouring •lasses. Few, indeed, of those who are habitually sub- jected to considerable and continued exertion survive their forty-fifth or fiftieth year. Exhausted at length by the constant recurrence of their daily task and imperfect nour- ishment, they die of premature decay long before attaining the natural limit of human existence. In those states of the system, again, such as fever, during the continuance of which most of the secretions are vitiated, and that of the gastric juice often entirely suppressed, and where food would consequently be hurtful rather than advantageous, appetite is scarcely felt, and loathing often occupies its place. But the moment that, by the diminu- tion of the disease, the secretions and exhalations begin to return to their healthy state, and nutrition is resumed, appetite begins to be again felt, and by and by becomes abundantly vigorous, in order to restore the system to its former state. The utmost caution, however, is still required tj its gratification, as a premature indulgence is almost certain again to stop the secretions and to produce a relapse. Ignorance of this principle among the community at large, and the consequent error of giving food when there is no demand for it, and no gastric juice to digest it, often do more to defeat the best laid plan of cure than the severity 40 INFLUENCE OF DISEASE ON APPETITE. of the disease itself. The sick man's friends, in their anxiety to support his strength, too frequently turn a deaf ear to every caution which is suggested, and stealthily administer sustenance when the system docs not require it, and when it serves only to aggravate the danger and increase the weakness of the patient. Since the first publi- cation of the preceding passage, I have seen a striking example of its truth. The patient was gradually recovering from inflammation of the chest, for the cure of which low diet was for a time indispensable. By way of supporting the diminished strength, the relations began to give, prema- turely and clandestinely, about double the quantity of food which was prescribed. For twenty-four hours an increase of strength was felt accordingly ; but very soon it passed into febrile excitement with a quick pulse and increased weakness. A dangerous relapse followed, and its cause was then found out. Abstinence was again enforced, and tartar emetic given to excite nausea. To the surprise of the very injucicious friends, the excitement began almost immediately s* subside and the strength to improve where they had just seen it fast giving way under a full diet. Appetite, ought to be observed, may, like other sensa- tions, be educated or trained to considerable deviations from the ordinary standard of quantity and quality—and this ob- viously for the purpose of enabling man to live in different climates and under different circumstances, and avoid being fixed down to one spot and to one occupation. In civilized life, however, we are accustomed to take undue advantage of this capability, by training the appetite to desire a greater quantity of food than what the wants of the system require, and stimulating its cravings by a system of cookery little in harmony with the intentions of Nature. But this is evidently an abuse, and no argument whatever against the sufficiency of its natural indications to lead us right. But lie most common source of the errors into which we are apt to faJl in taking appetite as our only guide, is un- questit nably the confounding of appetite with taste, and con- tinuing to eat for the gratification of the latter long after the foi ner is satisfied ; just as the dog already mentioned ate till the oesophagus was distended, although it did not experi'fice the slightest sensation of hunger.* In fact, the whole jc ience of a skilful cook is expended in producing * See p. 3* APPETITE A FAIR INDICATION OF WANT. 47 this willing mistake on our part; and he is considered fecidedly the best artiste whose dishes shall recomend them-