The Physiology of Digestion by Andrew Combe, M.B. (1837)
Part I. Chapter II. The Appetites of Hunger and Thirst
The Physiology of Digestion by Andrew Combe, M.D., Forth American Edition, was published By Marsch, Capen & Lyon in Boston in 1837. Andrew Combe was a physician in ordinary to their Majesties the King and Queen of the Belgians, and a Fellow of the Royal College of Physicians of Edinburgh. The third edition of this book was sold in 3000 copies. The text of this book of 310 pages will be found here, completely unchanged.
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. - 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.
In the preceding chapter we have endeavoured to show, first, that nutrition is required only bcause waste, and a deposition 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 sence 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 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 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 manifestly to proclaim that farther nourishemt is required for the support of the system; and our fist 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 exten, that a certain condition of the stoomach 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 striking upon the nerve of the eye; and the cause which excites the perception of sound, is at 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 itsefl is experienced in the brain, to which that impression is conveyed. Accordingly, just as in heatlh 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, indulgence in eating can be productive of nothing but mischief. Such an aberration is common in nervous and mental diseases, and not unfrequently adds greatly to thir 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 dyspeptic affections. (Dyspepsy, from the Greek words dys, bad, and pepto, I concoct, is synonymous with indigestion).
If the correctness of the preceding explanation of the sensation of hunger be thought to stand in need of confirmation, I would refer to the very conclusive experiments by Brachet 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 condition 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 consciousness of the state of the 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 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. (Brachet, Recherches Experimentales sur les Fonctions du Systéme Nerveux Ganglionare, chap. iii. Paris edition.)
Precisely similar results ensued when the nervous communication 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 grains of opium were then given to each at the same moment. The sound dog began immediately to feel the effects of the opium, and became stupid, while the other continued lying at the fireside for a long time, without any unusual appearence except a little difficulty of breathing. In like manner, when the experiment was repeated with that powerful poison nux vomica, upon two dogs similarly circumstanced, the sound one fell instantly into convulsions, while the other continued for a long time as if nothing had happened.
These results demonstrate, beyond the possibility of doubt, the necessity of a free nervous communication between 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 and the brain, enables us, in some measure, to understand the influence which mental emotion and earnest intellectual occupation exert over the appetite. A man in perfect health, sitting down to table with an excellent appetite, receives a letter announcin an unexpected calamity, and 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 of pleasing intelligence. In such cases, no one will imagine that the calamity destroys appetite otherwise than through the medium of the brain. Sometimes the feeling of loathing and disgust is so intense, as not ony to destroy appetite, but to induce sickness and vomiting, - a result which depends so closely on the state of the brain, that it is often induced even by mechanical injuries to that organ.
The analogy betseen the external senses and the appetite is, in various respects, very close. If we are rapt 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 beinig aware of either event. The same is the case with appetite. If the mind is deeply engaged, the suggestions of appetite are unperceived and unattended to - as 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 efficacy to mental occupation in deadening the sense of hunger, 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.
Many attempts have been made to determine what the peculiar condition of the stomach is which excites in the mind the sensation of hunger; but little success has hitherto attended them. For a long time it was imagined that the presence 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 is difficult, as in the above sentence, to avoid occasionally using expressions, and referring to processes, which have not previously been explained; but it would only lead to confusion and unnecessary repetition to stop at every page and introduce explanations, which, after all, the reader would scarcely understand on account of their brevity. In the present instance, therefore, when I allude to the process of digestion, it is better to refer the reader to the outline given at the beginning of Chapter IV., than to distract his attention by introducing it also here.) 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 general rule, that an interval of rest must follow the termination 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 substance 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, in the vessels or follicles by which it is secreted. But something more is required to render any of these explanations satisfactory; because there is an obvious relation between appetite and the wants of the system, which none of them take 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-être or internal comfort pervading 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. There is, in short, an obvious and active sympathy between 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 illustrated during recovery from a severe illness. "In convalescence from an acute disease," as is well remarked by Brachet, "the stomach digests vigorously, and yet the individual 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 continual sensation of want, which, however, is in this case only sympathetic of the state of the body." (Brachet, Recherches Experimentales sur les Fonctions du Systéme Nerveux Ganglionare, p. 181.). No testimony can be stronger than this.
The effects of exercise, also, show this connexion very clearly. 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 condition; whereas, i we exert ourselves sufficiently to give a general impetus to the circulation, and bring out moderate perspiration, but without inducing fatigue, we feel a lightness and energy of a very pleasurable description, and generally accompanied by a strongdesrie 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 system 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 stomach and all the other organs - in other words, of the readiness with which they accompany it in its departure fron health, and the corresponding aptitude of their disorders to produce derangement of the digestive function. Apparently for the purpose, among others, of thus intimately connecting the stomach 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 servere and often suddenly fatal result of a heavy blow on the pit of the stomach.
Without pretending to determine what the precise condition of the nerves of the stomach is. which, when conveyed to the brain, excites the sensation of appetite, I thing it sufficient for every practical purpose if we keep in mind that the co-operation of the nervous system is necessary 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 wich demand supplies of fresh materials - are most active; and in the lowest intensity when, from indolence and the cessation of growth, the demand is least. In youth, accordingly, when bodily activity is very great, and a liberal supply of nourishment is required both to repair waste and to carry on growth, the appetite is keener and less discrimination than at any other period of life, and, what is worthy of remark, as another admirable instance of adaptation, digestion is proportionally vigorous and rapid: whereas, in mature age, when growht is finished, and the mode of life more sedentary, the same abundance of aliment is no longer needed, the appetite becomes less keen and more select on 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 rejected, are disposed of with a degree of labour and difficulty that was formerly unknown.
When, however, the mode of life in mature age is active 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 positive disease does not exist, no other remedy is half so effectual.
It is highly important to notice this natural relation between waste and appetite, and between appetite and digestion; 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, amid the factitious calls and wants of civilized life, its suggestions are often perverted, and that hence we may err in blindly following every thing 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 dictates before we can implicitly rely on its guidance. If, when fairly consulted, its dictates are found to be erroneous, it will constitute the only known instance where the Creator has failed in the attempt to fulfil his own design - and assumption not only repugnant alike to feeling and to reason, but in fact altogether gratuitous. For the apparent discrepances which occasionally present themselves between the wants of the system and the dictates of appetite, are easily explicable on the more solid ground of our own ignorance and inattention.
Many practical errors arise from overlooking the relation which nutrition ought to bear to waste and growth. 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.
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 in towns and among females, who, having their time and employments entirely at their own disposal, carefully avoid every thing 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 functions. 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 cookery, 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 indulgence of appetite, the real enjoyment which its legitimate gratification afforded under different circumstances. Pursuing the pleasures of the table with the same ardour as before, they eat and dring freely and abundantly, and, instead of trying to acquire a healthy desire for food and increased powers of digestion by exercise, they resort to tonics, spices, wine, and other stimuli, which certainly excite for the moment, but eventually aggravate the mischief by obscuring its progress and extent. The natural result of this mode of proceeding is, that the stomach becomes oppressed 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 indulgence. So far, however, is the true cause of all these phenomena from being perceived even then, that a cure is sought, not in 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 morbid craving which they only silence for a little. Some, of course, suffer in a greater, and others in a less degree, according 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 overcharged, 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 indolent to eat and drink less than the busy and laborious, is established not only by the diminished appetite and impaired 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 noticing 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 demant for nourishment, in order to supply the expenditure of vital force created by these exertions. Compared 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 development," 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 intuguments during its continuance in the larva state, consumes a vast quantity of food compared with the size of its body; and hence we find it provided with a digestive apparatus of considerable size." (Roget´s Bridgewater Treatise on Animal and Vegetalbe Physiology, vol ii, p 112.)
In thus insisting on regular boyd 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 (Principes of Physiology, &c., chapters IV. and V.), I 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 possess; 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 I 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 thtat the European is intended by the nature to live in a tropical climate; because, if he is not, his condition under such an influence 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 instance there is less contradiction than might be supposed, for the waste of the system being chiefly fluid, excites - not 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 between 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 struggling 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 experiment; 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 the the excretory functions, such as perspiration or the urinary of alvine discharges, by means of which the system is relieved much in the same way as by active exercise. In others, again, the day of reckoning is merely delayed, and there is habitually present a state of repletion, which clogs the bodily functions, and may lead to sudden death by some acute disease, when 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 desert 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 gained at the expense of a very full habit of body, and a liability to frequent and profuse perspirations, and to severe attacks of bowel complaint, endangering life; so that even they cannot by any means be regarded as real exceptions to the general rule.
It is, then, no idle whim to the physician to insist on active exercise as the best promotor of appetite and digestion. Exercise is, in fact, the condition without which exhalation and excretion cannot go on sufficiently fast to clear the system of materials previously taken in; and where no waste is incurred, no need for a fresh supply, and consequently, in a healthy state of the system, no natural appetite, can exist. It is therefore not less unreasonable that vain for any one to insist on possessing, at the same time, the incompatible enjoyments of luxurious indolence and a vigorous 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 been 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 expenditur of energy and substance takes place that what their deficient 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 nevertheless very palpable manifest in the depressed buoyancy, early old age, and shorter lives of the labouring classes. Few, indeed, of those who are habitually subjected 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 nourishment, 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 the stomach itself is weakenedd, 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 diminuation 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 in 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, often do more defeat the best laid plan of cure than the severity 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 does not require it, and when it serves only to aggravate the danger and increase the weakness of the patient.
Appetite, it ought to be observed, may, like other sensations, be educated or trained to considerable deviations from the ordinary standard of quantity and quality - and this obviously 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.
The most common source, however, of the errors into which we are apt to fall in taking appetite as our only guide, is unquestionably the confounding of appetite with taste, and continuing to eat for the gratification of the latter long after the former is satisfied. In fact, the whole science of a skilful cook is expanded in producing this willing mistake on our part; and he is considered decidedly the best artiste whose dishes shall recommend themselves most irresistibly to the callous palate of the gourmand, and excite on it such a sensation as shall at least remind him of the enviable excellence of a natural appetite. If we were willing to limit the office of taste to its proper sphere, and to cease eating when appetite expressed content, indigestion would be a much rarer occurence in civilized communities than it is observed to be.
Viewed, then, in its proper light, appetite is to be regarded as kindly implanted in our nature for the express end of proportioning the supply of nourishment to the wants of the system; and if ever it misleads us, the fault is not in its unfitness for its object, but in the artificial training which it receives at our own hands. When we attend to its real dictates, we eat moderately, and at such intervals of time as the previous exercise and other circumstances render necessary; and in so doing, we reap a reward in the daily enjoyment of the pleasure which attends the gratification of healthy appetite. But if we err, either by neglecting the timely warning which it gives, or by eating more than the system requires, mischief is sure to follow. In the former case, waste continues to make progress till the body becomes exhausted; and in almost exact proportion do the cravings of appetite become more and more intense, till they pass into those of uncontrollable hunger, which overthrows all obstacles, and seeks gratification at the risk of life itself. In the latter case, indigestion, gloomy depression, and repletion, with its concomitant evils, make their appearance, and either imbitter or cut short existence.
Mischief sometimes arises also from people not being sufficiently aware, that, in common with other sensations, appetite may be so far deranged by disease as to give very incorrect and unnatural indications. It often happens, for example, that a patient shivers and complains of cold, when we know by the thermometer that the heat of the skin is really above instead of below the natural standard. In like manner, in some morbid states of the nervous system, a craving is often felt which impels the patient to eat, but which is not true hunger; and here food, if taken, is digested with great difficulty. Occasionally, on the other hand, no desire for food is experienced when the system really needs it, and when it woud be digested with ease if introduced into the stomach. Esquirol alludes to cases of this description, and I have met with similar examples. Voisin also mentions, that, in the Hospital ov Incurables in Paris, there are som idiots so low in the scale of intelligence as to make no attempt to take the food which is placed before them, although they eat and digest readily when fed by others. Sometimes, again, appetite is depraved in quality, and the patient desiderates the most nauseous and repulsive kinds of food, such as earth, chalk, coals, and excrement. There are states, too, in which the appetite is prodigiously increased, and the patient consumes incredible quantities of food, - which, however, are very imperfectly digested. Charles Domery, for instance, when a French prisoner at Liverpool, consumed, in one day, four ponds of cow´s udder and ten pounds of raw beef, with two pounds of tallow candles and five bottles of porter; and, although allowed the daily rations of ten men, he was still not satisfied. Baron Percy speaks of another man, who ate twenty-four pounds of beef in as many hours, and thought nothing of swallowing a dinner prepared for fifteen German boors. I once attended a patient who was afflicted with a similar inordinate craving, and whose only pleasure was in eating. In such cases no restraint except actual coercion is sufficient to prevent indulgence; but the craving itself is as much the product of disease as the shivering in the beginning of fever, and can no more be removed by reasoning than the sensation of cold can be removed by telling a patient that his skin is thermometrically warm. But these, being cases of disease, do not in any degree militate against the accuracy of the exposition above given of the healthy uses of appetite.
The general considerations which I have just submitted to the reader on the subject of appetite for food, apply so closely to the sensation of Thirst, that to enter into any detail concerning the latter would be little else but to be guilty of repetition. I shall therefore limit myself to a very few remarks.
Thirst is generally said to have its seat in the back of the mouth and throat; but the condition of these parts is mere local accompaniment of a want experienced by the whole frame, and perceived by the nervous system. Local applications accordingly, go but a short way in giving relief, while the introduction of fluids by any other challel - by immersion in a bath, by injection into the veins, or through an external opening into the stomach - is sufficient to quench thirst without the liquid ever touching the throat. The affection of that part, therefore, is merely a result of the state of the system, and not itself the cause of thirst.
Thirst, or a desire for liquids, is experienced in its greatest intensity when the secretion and exhalation of the animal fluids is most active; and it is consequently most urgent i summer, in warm climates, and in persons engaged in severe exertion, particularly if exposed at the same time to a heated atmosphere. Blacksmiths, glassblowers, engineers, and others, whose employment exposes them to the heat of furnaces, and in whom perspiration is excessive, are accordingly almost constantly under the influence of thirst; whereas those who are employed in professions requiring only moderate exertion in a temperate atmosphere, and in whom the fluid secretions are very moderate, rarely experience the sensation in an urgent degree.
Thirst varies in intensity also according to the nature of food. If the diet be hot and stimulating, such as results from a free admixture of spices or salt, the desire for drink is greatly increased. The same thing happens if the food be of a dry and solid nature. The purpose of the increased thirst in the former circumstance, is manifestly to dilute and diminish the excess of stimulant, and thereby prevent the injury which it would otherwise inflict. The same principle explains the thirst experienced by those who dring too much wine. In instances of this kind, I have heard great thirst experienced by those who drink too much wine; and yetm on abstaining from the latter, the thirst very soon dissappear.
Continued thirst, it is well known, is much more intolerable than continued hunger. The mass of circulating fluid in the body is very great, and, as the various excretions consist chiefly of fluid matter, it necessarily happens, that when these have been eliminated for a considerable time without any liquid being received into the system, the proportion of solid matter in the body becomes thicker, and changed in quality, and much more irritating than it is in its natural state. The craving of thirst is thus generally rendered more urgent and overpowering than that of hunger.
In Asiatic Cholera, the watery portion of the blood, on which its fluidity depends, is drained off with frightful rapidity; and the result is, in the first place, an almost complete stoppage of the circulation, and, in the second, a constant craving fro drink to supply the place of the lost serum, which consists chiefly of water, holding some of the alkaline salts in solution. This circumstance explains, in some degree, the extraordinary effects which have been produced, even in the worst stages of the disease, when life seemed almost extinct, by injecting large quantities of saline solutions into the veins. Patients apparently on the verge of existence, cold, pulseless, and inanimate, have, in the course of a few minutes, been enabled by this means to situ up in bed, and to exhibit all the signs of restored strength and health. The effect, it is true, was rarely permanent, but for the time it was so wonderful as often to look like restoration from the dead.
Fluids taken into the stomach, it is proper to observe, are not subjected to the slow process of digestion, but are absorbed directly into the system; so that, when we take a moderate draught, the whole of it is taken up from the stomach in a very few minutes. Keeping in view this fact, and the above striking illustration of the influence of the condition of the blood upon the body at large, it becomes easy to conceive why, in a state of exhaustion from abstinence, drink should be more speedily restorative and refreshing than food.
Thirst, like appetite for food, is intended to direct us when and in what quantity we ought to drink; and so long as we confine ourselves to the fluids whit which nature provide us, there is little chance of our going far wrong by listening to its calls. But when we coome to the use of fermented and stimulating liquors, which excite a thirst not recognised by nature, the principle ceases to operate. At present, however, my observations apply entirely to the former, and I shall touch upon these other liquids when treating of diet in a subsequent part of this volume.