: DIGESTION AND DIETETICS. THE PHYSIOLOGY OF DIGESTION CONSIDERED WITH RELATION TO THE PRINCIPLES OF DIETETICS. BY ANDREW COMBE, M.D. FELLOW OF THE ROYAL COLLEGE OF PHYSICIANS IN EDINBURGH, AND CONSULTING PHYSICIAN TO THEIR MAJESTIES THE KING AND QUEEN OF THE BELGIANS. SECOND EDITION REVISED AND ENLARGED. " Nor is it left arbitrary, at the will and pleasure of every man, to do as he list ; after the dictates of- a depraved humour and extravagant pliancy r , to live at what rate he pleaseth ; but every one is bound to ob- serve the Injunctions and Law of Nature, upon the penalty of forfeiting their health, strength, and liberty, the true and long enjoyment of them- selves.'* MAINWATRJNGE. EDINBURGH: MACLACHLAN & STEWART; AND SIMPK1N, MARSHALL & CO. LONDON. MDCCCXXXVI. PRINTED BY NEILL & CO. OLD FISHMARKET. c ADVERTISEMENT TO THE SECOND EDITION. THE first edition of the present volume consisted of 2000 copies, and has been exhausted in little more than five months. Already, also, it has been twice reprinted in the United States. This success is ex- tremely gratifying, and shews that the desire for in- formation on the subject of the human constitution, is rapidly extending in proportion as it is discovered to be perfectly within the comprehension of every or- dinary capacity, and to be directly and easily appli- cable to the farther improvement of the moral and physical condition of man. The edition now offered to the public has been carefully revised, and about twenty pages of new matter have been added. Still, I fear, that many im- perfections remain, which leisure and more confirmed VI ADVERTISEMENT. health might have enabled me to remove, but which, under present circumstances, I feel compelled to leave to the good-natured indulgence of the reader. It has been suggested by a professional critic for whose judgment I feel the utmost deference, that " the work would really have been more useful if the phy- siological or introductory part had been more con- densed ;*" as much of it will, he thinks, be neither readi- ly comprehended, nor usefully retained by the general reader.* My only reason for not acting on this sug- gestion is, that I regard the exposition of the laws of digestion of which that part consists, as the foundation -on which all the dietetic rules contained in the second part must necessarily rest, and am therefore extreme- ly anxious that their nature and mode of operation should be thoroughly understood by the ordinary reader, even at the risk of too great minuteness. I am quite aware that the detail into which I have entered must appear tedious to every well educated practi- tioner ; but as the book was intended more for the ge- neral than for the medical reader, the latter is evident- ly a less competent judge in this particular matter than the former. On referring, accordingly, to an unpro- fessional critic of no small ability and reputation, we find him of an entirely opposite opinion. For" Of * British and Foreign Medical Review, vol. ii. p. 378. ADVERTISEMENT. vii the two divisions of the book," he thinks, " the FIRST is the most satisfactory and interesting, from the na- ture of its subject and the popular novelty of much of the information it imparts, or the force and fresh- ness with which obvious truths are presented."* And as other non-medical reviewers concur in this decision, I feel bound to attach more weight to them in what more especially concerns the class of readers to which they belong, and to retain the whole of the part ob- jected to. In a purely medical question, on the other hand, I would as unhesitatingly have yielded to the judgment of the professional critic. Spectator, 7th May 1836. EDINBURGH, 8 ALVA STREET, November 1. 183C. CONTENTS PREFACE, . ,V i' ' . xvi PART I. PHYSIOLOGY OF DIGESTION. CHAPTER I. INTRODUCTORY REMARKS. Waste or loss of substance always attendant on action lu 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 connection with their food Animals, being obliged to wander, receive their food at intervals into a stomach Nu- trition 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 Ap- petite to regulate the supplies of food, . ^"- i_io CHAPTER II. THE APPETITES OF HUNGER AND THIRST. Hunger and Thirst, what they are Generally referred to the sto- mach and throat, but perceived by the brain Proofs and il- X CONTENTS, lustrations Exciting causes of hunger Common theories un- satisfactory 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 of injection of water into the veins in cholera Uses of thirst, and rules for gratifying it, . 1 1-39 CHAPTER III. MASTICATION, INSALIVATION, 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, 40-57 CHAPTER IV. ORGANS OF DIGESTION THE STOMACH THE GASTRIC JUICE. Surprising power of digestion Variety of sources of food All structures, however different, formed from the same blood General view of digestion, chymification, chylification, sangui- fication, 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 commu- nication between the brain and stomach Their relation to un- digested food Animals not conscious of what goes on in the CONTENTS. XI stomach Advantages of this arrangement The gastric juice the grand agent in digestion Its origin and natuie Singular case of gunshot wound making a permanent opening into the stomach Instructive experiments made by Pir Beaumont Important results, 58-108 CHAPTER V. THEORY AND LAWS OP DIGESTION. Different theories of Digestion Concoction Fermentation Pu- trefaction Trituration Chemical solution Conditions or laws of digestion Influence of gastric juice Experiments il- lustrative 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 Ta- ble of results Animal food most digestible Farinaceous next Vegetables and soups least digestible Organs of digestion simple in proportion to concentration of nutriment Digesti- bility depends on adaptation of food to gastric juice more than on analogy of composition Illustrations. No increase of temperature during digestion Dr Beaumont's summary of in- ferences, ~^*P -t>* / . . 109-151 CHAPTER VI. CHYLIFICATION, AND THE ORGANS CONCERNED IN IT. delineation Not well known Organs concerned in it The intestinal canal Its general structure Peritoneal coat- Mesentery Muscular coat Uses of these Air in intestines Uses of Mucous coat Analogous to skin The seat of xii CONTENTS. excretion and absorption Mucous glandsAbsorbent vessels Course of chyle towards the heart Nerves of mucous coat Action of bowels explained Individual structure of intes- tines The Duodenum Jejunum and Ileum Liver and pancreas concerned in chylification Their situation and uses Bile, its origin and uses The pancreas Its juice The jejunum described The ileum Ccecum Colon and Rec- tum 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 Dupuytren, 152- PART II. THE PRINCIPLES OF DIETETICS VIEWED IN RE- LATION TO THE LAWS OF DIGESTION. CHAPTER I. TIMES OP EATING. The selection of food only one element in sound digestion Other conditions essential Times of eating No stated hours for eating Five or six hours of interval between meals generally sufficient But must vary according to circumstances Habit has much influence Proper time for breakfast depends on con- stitution, health, and mode of life Interval required between breakfast and dinner Best time for dinner Circumstances in which lunch is proper Late dinners considered Their pro- priety dependent 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 illus- trations but requires ihe observance of principle in our rules, -217 V * CONTENTS. xiii 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 er- ror 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 ex- cess in servant-girls from the country, dressmakers, &c. Mis. chief from excessive feeding in infancy Rules for preventing this Remarks on the consequences of excess in grown per. sons Causes of confined bowels explained And necessity of fulfilling the laws which God has appointed for the regulation of the animal economy inculcated, . . . 218-250 CHAPTER III. OF THE KINDS OF FOOD. What is the proper food of man ? Food to be adapted to constitution and circumstances Diet must vary with time of life Diet in infancy The mother's milk the best Substitutes for it Over-feeding a prevalent error Causes which vitiate the qua- lity of the milk Regimen of nurses Weaning Diet after weaning Too early use of animal food hurtful Diet of child- ren in the higher classes too exciting and produces scrofula- Mild food best for children Incessant eating very injurious Proper diet from childhood to puberty It ought to be full and nourishing but not stimulating Often insufficient in boarding- school* Diet best adapted for different constitutions in mature age Regimen powerful in modifying the constitution, mental as well as physical Farther investigation required, . 251-287 XIV CONTENTS. CHAPTER IV. CONDITIONS TO BE OBSERVED BEFORE AND AFTER EATING. General laws of organic activity apply to the stomach as well as to other parts Increased flow of blood towards the stomach dur- ing digestion Hence less circulating in other organs and consequently less aptitude for exertion in them Bodily rest and mental tranquillity essential to sound digestion Rest al r ways attended to before feeding horses Hence also a natural aversion to exertion immediately after eating Mischief done by hurrying away to business after meals Severe thinking hurtful at that time Playful cheerfulness after dinner condu- cive to digestion 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, .... 288-303 CHAPTER V. ON DRINKS. Thirst the best guide in taking simple drinks Thirst increased by diminution of the circulating fluids The desire for liquids ge- nerally an indication of their propriety Much fluid hurtful at meals Most useful three or four hours later The tempera- ture 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 cau- tion used Cold water more dangerous than ice when the body is overheated Tepid drinks safest and most refreshing after perspiration Kinds of drink Water safe for every constitu- tion Wine, spirits, and other fermented liquors, too stimu- lating for general use, but beneficial in certain circumstances Test of their utility,.- : 4 ;,,.;. .... 304-323 CONTENTS. XV CHAPTER VI. ON THE PROPER REGULATION OF THE BOWELS. Functions of the intestines The action of the bowels bears a natu- ral 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 Con. eluding remarks, 324-339 INDEX, 341-250 WOOD-CUTS. Under-jaw, 41. Thoracic and Abdominal Viscera, 66. Human Stomach, 67. Stomach of a ruminating animal, 69. Villous Coat of the Stomach, 75. Opening into the stomach of Alexis St Martin, 88. Abdominal Viscera, 155. Transverse section of the Abdomen, 157. Lacteals and Thoracic Duct, 163. Thoracic Duct, 166. Contents of the Abdomen after removal of the Intestines, 171. Mucous Coat of the Duodenum, 172. PREFACE. THE present volume is essentially a continuation of the work first published about two years ago, un- der the title of " The Principles of Physiology ap- plied to the Preservation of Health and to the Im- provement of Physical and Mental Education ;" and its object is the same namely, to lay before the pub- lic a plain and intelligible description of the structure and uses of some of the more important organs of the human body, and to shew how information of this kind may be usefully applied, not only in the pre- vention of suffering, but in improving the physical, moral, and intellectual condition of man. In " The Principles of Physiology," the struc- ture and functions of the skin, muscles, bones, lungs, and nervous system, the laws or conditions of their healthy action, and the unsuspected origin of many of their diseases in infringements of these laws, were explained in succession at considerable length ; and XV111 PREFACE. the means by which their health and efficiency might best be secured were pointed out. It was stated that, in selecting these organs as subjects for dis- cussion, I had been guided by the desire to notice in preference those functions which are most influen- tial in their operation on the general system, and at the same time least familiarly known ; and that, if the attempt to convey the requisite information in a manner suited to the general reader should prove suc- cessful, I would afterwards prepare a similar account of others, in the right understanding and manage- ment of which our interest is not less deeply involved, but in regard to which much ignorance continues ne- vertheless to prevail, even among the most liberally educated classes of society. The numerous proofs which I received of the uti- lity of my former work, not only from professional and literary journals, but also from individuals pre- viously unknown to me, many of them guardians and instructors of youth, speaking from personal ex- perience, together with the rapid sale of four large editions in little more than two years, soon completely satisfied me that I had neither been deceived as to the real importance of physiological knowledge to the general public, nor been altogether unsuccessful in the method of conveying it. Thus encouraged, ac- cordingly, I cheerfully resumed my labours, and, from PREFACE. XIX materials which had been long accumulating, began the preparation of the treatise now submitted to the indulgent consideration of the reader. The matters discussed on the present occasion re- late chiefly to the function of Digestion and the prin- ciples of Dietetics ; and in selecting them I have been guided by the same principle as before. It may, at first sight, be doubted whether I have not exceeded proper bounds in thus dedicating a whole volume to the consideration of a single subject ; but the more we consider the real complication of the function of Di- gestion, the extensive influence which it exercises at every period of life over the whole of the bodily or- ganization, the degree to which its morbid derange- ments undermine health, happiness, and social use- fulness, and especially the share which they have in the production of scrofulous and consumptive as well as of nervous and mental affections, we shall become more and more convinced of the deep practical in- terest which attaches to a minute acquaintance with the laws by which it is regulated. In infancy, er- rors in diet, and derangement of the digestive organs, are admitted to be among the principal causes of the striking mortality which occurs in that period of life. In youth and maturity, the same influence is recog- nised, not only in the numerous forms of disease di- rectly traceable to that origin, but also in the univer- XX PREFACE. sal practice of referring every obscure or anomalous disorder to derangement of the stomach or bowels. Hence, too, the interest which has always been felt by the public in the perusal of books on Dietetics and Indigestion ; and hence the prevailing custom of using purgatives as remedies for every disorder, very often with good, but not unfrequently with most injurious effects. Numerous and popular, however, as writings on Dietetics have been, and excellent as are many of the precepts which have been handed down by them from the earliest ages, sanctioned by the warm approval of every successive generation, it is singular how very trifling their influence has been, and continues to be, in altering the habits of those to whom they are ad- dressed. In a general way, we all acknowledge that diet is a powerful agent in modifying the animal eco- nomy ; yet, from our conduct, it might justly be in- ferred, that we either regarded it as totally devoid of influence, or remained in utter ignorance of its mode of operation, being left to the guidance of chance alone, or of notions picked up at random, often at va- riance with reason, and, it may be, in contradiction even with our own daily experience. It has been alleged by a friendly critic of the first edition, that the author is too sanguine in expect- ing that the mere communication of knowledge will PREFACE. XXI suffice to alter the habits of the race, and that, al- though the information conveyed in the present vo- lume may be turned to account by third parties by mothers and nurses, for example " yet with respect to the direct effect upon eaters," slender results must be anticipated. " The world," it is wittily added, " will read, admire, and applaud Dr Combe on Di- gestion and Dietetics, and then go on in its usual way eating what it likes, and digesting' what it can" The Author, however, never entertained the hope that his work would immediately produce the slight- est perceptible change in the general practices of so- ciety, or that many healthy men of mature age and confirmed habits would forsake their accustomed regi- men merely because it was shewn to be at variance with the laws of Nature. But as human conduct is in some measure influenced by knowledge, he is still confident enough to believe, that, among valetudina- rians and the young of both sexes, whose habits are not formed, and numbers of whom err as much from ignorance as from the force of passion, many may be found who will be glad to obtain the guidance of knowledge and principle in the regulation of their mode of life ; and that even many parents, who may not have resolution enough to forsake mischievous indulgences to which they have long been accustom- ed, may nevertheless be anxious to avail themselves b XX11 PREFACE. of any assistance on which they can depend for the better bringing up of their children. If in these ex- pectations he is not too sanguine, the future advantage to the race from the present diffusion of dietetic know- ledge is as certain, and almost as encouraging, as if its effects were instantaneous on both old and young. In the march of human improvement, months and years count but as moments. The men of to-day will soon have acted their part, and give place to those who are now with youthful energy adding to their knowledge, and throwing off a portion of the prejudices of their fathers. They in their turn will speedily be succeeded by their children, and the discoveries of the one gene- ration will thus become the established and influential truths of the next. Each individual change in the habits of society may be so slow and minute as at the moment to escape our notice, but it is not on that ac- count the less real. Nobody who compares the coarse feeding and riotous convivialities of our forefathers, at the beginning of last century, with the more refined and temperate habits of the present day, will think of denying that a prodigious step has been made in the interval even with respect to eating and drinking, which the critic seems to consider as so much beyond the influence of reason. And yet, if we take any single year of the whole century, we shall be unable to particularize any marked reformation which took PREFACE. XXlli place within its limits. This being the case, then, can we, their descendants, maintain that we are ar- rived so nearly at perfection as to leave no room for corresponding improvement in our day ? My convic- tion is so much the reverse, that it seems to me certain that our onward progress will continue through gene- rations 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 constitu- tion, 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 applica- bility of the views which are unfolded. On such con- siderations do I ground my hope that the present volume, notwithstanding its numerous defects, will (in so far as it really embodies truths of practical im- portance) contribute in its own limited sphere to the general end. The real cause of the little regard paid to dietetic rules anjd it is of consequence to remark it is not so much indifference to their influence, or even the absolute want of valuable information, as the faulty manner in which the subject is usually considered. In many of our best works, the relation subsisting be- tween the human body on the one hand, and the quali- ties of alimentary substances on the other, is alto- XXIV PREFACE. gether lost sight of, although it is the only solid prin- ciple 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 individual constitution, as modified by age, sex, season, and circumstances, or to the observance of the fundamental laws of digestion. And hence, although these conditions are not unfrequently 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 erro- neous conclusions are 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 guiding principle to direct their experience, and test the accuracy of the precepts laid down to them for the regulation of their conduct, that many per- sons begin by being bewildered by the numerous dis- crepancies which they meet with between facts and doctrine, between counsel and experience, and end by becoming entirely sceptical on the subject of all dietetic rules whatever, and regarding them as mere theoretical effusions, based on fancy, and undeserving of a moment's consideration. The true remedy for this state of things is, not to PREFACE. XXV turn away in disgust and despair, but to resort to a more rational mode of inquiry certain that, in pro- portion 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 re- sults. 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 application : but beyond this, I lay no claim to originality ; and if I have any where used expressions which may seem either to do injustice to others or to arrogate too much credit to myself, it has been en- tirely without any such design, and, consequently, I will be prompt to acknowledge my error and rectify the involuntary mistake. In preparing the present volume for the press, I have derived the utmost advantage from a very valu- able work by Dr Beaumont, an American writer, which though faulty in its arrangement, and neces- sarily defective in many essential particulars con- tains an authentic record of some of the most curious and instructive observations which have ever been XXVI PREFACE. made on the process of digestion. That excellent and enlightened physiologist had the rare good for- tune to meet with a case where an artificial opening into the stomach existed, through which he could see every thing that took place during the progress of healthy digestion ; and, with the most disinterested 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 con- ducted experiments. Of the results thus obtained, I have not scrupled to make the freest and most ample use not from considering them as positively new (for even Dr Beaumont lays little claim to the merit of a discoverer), but because they come before us so en- tirely freed from the numerous sources of error and doubt which formerly impaired their value, that they can now, for the first time, be safely trusted as practi- cal guides in the science of dietetics. From Dr Beaumonf s work, also, being still inaccessible to the British reader, it is a bare act of justice towards him, and also the best way of fulfilling the objects he had m view, to make its contents known as widely as pos- sible : for wherever they are known, they will be ac- knowledged to redound to his credit, not less as a man than as a philosopher, PREFACE. XXVH Objections have been stated to several of the repe- titions which occur in the following pages. The only apology I have to offer for them is, that I committed them deliberately, because they seemed to me neces- sary to ensure clearness, and because the intimate manner in which the different functions are connect- ed 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 leniently overlooked. Those who wish to study more fully the subject of Dietetics, will find much useful information in Dr Hodgkin's " Lectures on the Means of Promoting and Preserving Health ;" Professor Dunglison " On the Influence of Atmosphere and Locality, Change of Air and Climate, Seasons, Food, Clothing, Bath- ing, Exercise, Sleep, Corporeal and Intellectual Pur- suits, &c. &c. &c. on Human Health ;" Dr Paris " On Diet ;" and Dr Kilgour's " Lectures on the Ordinary Agents of Life, as applicable to Therapeu tics and Hygiene." CHAPTER I. GENERAL VIEW OF THE OBJECTS AND LAWS OP NUTRITION. Waste or loss of substance always attendant on action. In the vegetable and animal kingdoms waste is greater than in the physical. 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 aud waste are greatest In vegetables the same causes which increase these processes also stimulate nutrition. But animals require a mo- nitor to warn them when food is needed. The sense of Appetite an- swers this purpose. The possession of a stomach implies a sense of Appetite to regulate 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 understood, that it is aii important aim in mechanics to discover the best means of reducing to the lowest possi- ble 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 re- A 2 WASTE ALWAYS ATTENDANT ON ACTION. newal become indispensable 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 por- tion of its substance. The smoothest and most accurate- ly formed wheel, running along the most level and po- lished railroad, parts with some portion 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 faith- ful ; and I venture to mention it, because it affords one of the best specimens of the operation of a principle, 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 every thing passing around us ; and so much human ingenuity is exercised to counteract its effects, that no re- flecting person will dispute the universality of its opera- tion. 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 EVEN IN LIVING BODIES. living bodies as constituting exceptions to the rule. On more careful examination, however, it will appear that waste goes on in living bodies not only without any in- termission, but with a rapidity immeasurably beyond that which occurs in inanimate 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 operations are at a close. The same thing holds true in the animal kingdom. So long as life continues, a copious exhalation from the skin, the lungs, the bowels, and the kidneys, 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 circulation, and add something to the ge- neral 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 ; whereas, af- ter 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 it- self. In the physical or inanimate world, what is once lost or 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 LIVING BODIES CAN REPAIR THEIR WASTE. course of time it must either be laid aside as useless, or be remodelled by the hand of the workman. But living bodies, whether vegetable or animal, possess the distin- guishing- 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 six pounds of substance by the ordinary channels of excretion, possessed no means of repairing the loss, his organization would speedily de- cay 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 becomes incapable of carry- ing 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 be- came 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 expendi- ture 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 compensating its occurrence. VEGETABLES ALWAYS IN CONTACT WITH THEIR FOOD. 5 in surveying the respective modes of existence of ve- getables and of animals, with the view of ascertaining by what means this compensation is effected, the first strik- ing difference 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 in- fluence. 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 still has no option : it must grow up in rank and unhealthy luxuriance, in obedience to an impulse which it cannot resist. At all hours and at all seasons it is at home, and in direct com- munication with the soil from which its nourishment is extracted. And being thus without ceasing in contact with its food, it requires no storehouse in which to lay up provision, but receives immediately from the earth, and at every moment, all that is necessary for its suste- nance. But it is otherwise with animals. These not only en- joy 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 ex- ternal substances, they would be torn asunder at every movement, and the animals themselves exposed either to die from starvation, or to forego the exercise of the 6 ANIMALS RECEIVE FOOD AT INTERVALS. higher functions for which their nature is adapted. But the necessity for a constant change of place being impo- sed on them, a different arrangement became indispen- sable for their nutrition : and the method by which the Creator has remedied the inconvenience is not less admi- rable than simple. To enable the animal to move about and at the same time to maintain a connexion with its food, He has provided it with a receptacle or stomach, where it is able to store up a supply of materials 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 ade- quate to its wants ; and the small nutritive vessels imbibe 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 re- ceptacle 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 wiuter, when the leaves and flow- RELATION BETWEEN WASTE AND NUTRITION. 7 ers have passed away, and vegetable life is in repose, little nourishment is needed, and the circulation of the sap is 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 attended 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 diminished. This is uniformly the case in win- ter; and many circumstances shew that the change is really owing to the causes mentioned above, and not to any thing inherent in the constitution of the vegetable itself. In tropical climates, for example, where heat, light, and moisture abound, vegetable 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 8 RELATION EXISTS BETWEEN WASTE AND NUTRITION, to auticipate the natural order of the seasons, as to ob- tain 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 eariy supply of oar markets, is, in truth, founded on the principle we are now discussing ; and by the regulated application of heat, light, and moisture, we are able to hasten or to retard, to a very considerable extent, the ordinary stages of vege- table 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. If, by the applica- tion of heat, we have stimulated it to premature growth and foliage, we must at the same time provide for it an adequate supply of food, otherwise its activity will ex- haust itself, and induce premature decay. Hence the regular watering which greenhouse plants require. But if we have retarded its progress and lowered its vitality by excluding heat and light, the same copious nourish- ment will not only be unnecessary, but will probably do harm by inducing repletion 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, nutri- tion is always most active when the greatest expenditure of material 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 processes are completed as summer advances, and IN BOTH VEGETABLES AND ANIMALS. 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 nourish- ment suffices, and the sap no longer circulates in the same profusion. In autumn, again when the fruit ar- rives" at maturity, the leaves begin to drop off, and the activity of vegetable life suffers abatement, 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 expendi- ture of material, an increased quantity of food is invari- ably required; and, on the other hand, where no new substance is forming, and where, from bodily inactivity, little loss is sustained, a comparatively 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 immediate- ly from one kind and quantity of nourishment to another, in order to adapt their nutrition to the erer-varying de- mands made upon the system they evidently stand in need of some provision to enforce attention when nour- ishment is necessary, and to enable them always to pro- portion the supply to the real wants of the body. Not being, like vegetables, in constant connection with their aliment, they might suffer from neglect if they did not pos- sess some contrivance to warn them in time when to seek 10 APPETITE NECESSARY AS A GUIDE. and in what quantity to consume it. But in endowing animals with the sense of Appetite, or the sensations of Hitnger and Thirst generally included under it, the Crea- tor has guarded effectually against the inconvenience, and given to them a guide in every way sufficient for the purpose. The very possession of a stomach or receptacle, into which food sufficient for a shorter or longer period canbe in- troduced at one time, and which we have already remarked as characterizing all animals from the lowest to the high- est, almost necessarily implies the co-existence 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 con- stantly 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 safe- guard in the sensations of hunger and thirst, but more- over, 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 im- portant 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. ( 11 ) 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 illustrations. Exciting causes of hunger Common theories unsatisfactory Hun- ger sympathetic of the state of the body as well as of the stomach Uses of appetite Relation between waste and appetite Its prac- tical importance Consequences of overlooking it illustrated by analogy of the whole animal kingdom Disease from acting in op- position to this relation Effect of exercise on 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 chiolera Uses of thirst, and rules for gratifying it. IN the preceding chapter, I endeavoured to shew, fast, that nutrition is required only because waste, and a de- position of new particles, are continually going on, so that the body would speedily become exhausted if its consti- tuent 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 ne- glect 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 12 SEAT OF THE SENSATION OF HUNGER. necessary, 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 implied, except where it is otherwise plainly ex- pressed), 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 sus- tenance. But to make this perfectly evident, a few ge- neral 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 expe- rience, any more than sweetness or sourness could be understood without tasting sweet or sour objects. Their end is manifestly to proclaim that farther nourishment is required for the support of the system ; and our first business is, therefore, 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 ex- tent, 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 & sense of the con- dition of the stomach is conveyed through the medium of HUNGER A MENTAL SENSATION. 13 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 striking upon the nerve of the eye ; and the cause which excites the perception of sound, is the atmospherical vibrations 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 impression made on the nerves of the stomach ; but the feeling itself is expe- rienced in the brain, to which that impression is convey- ed. 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 per- ceived unless an object be presented to the eye, so ia 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, in- dulgence in eating can be productive of nothing but mis- chief. Such an aberration is common in nervous and mental diseases, and not unfrequently adds greatly to their severity and obstinacy. In indolent unemployed persons, who spend their days in meditating on their own 14 NERVOUS COMMUNICATION BETWEEN THE feelings, this craving is very common, and from being re- garded and indulged as if it were healthy appetite, is pro- ductive of many dyspeptic affections.* If the correctness of the preceding explanation of the sensation of hunger be thought to stand in need of con- firmation, I would refer to the very conclusive experi- ments by Brachet of Lyons, as setting the question en- tirely 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 condition of the stomach. He then placed food with- in 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 consciousness 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 sense of taste; for on removing the food at the beginning of the experiment to the dis- tance of even a few inches, it looked on with indifference, and made no attempt either to follow the dish or to pre- vent its removal.f Precisely similar results ensued when the nervous sympathy between the stomach and brain was arrest- ed by the administration of narcotics. A dog suffer- * Dyspepsia (from the Greek words tvj, dus, bad, and