Among the operative part of the community we meet with innumerable examples of an opposite condition of the system, where, from excess of labour, a greater expenditure of energy and substance takes place than 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 palpably 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 that of the gastric juice often entirely suppressed, and where food would consequently be hurtful rather than advantageous, appetite is scarcely felt, and loathing often occupies its place. But the moment that, by the diminution 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, and no gastric juice to digest it, often do more to 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. Since the first publication of the preceding passage, I have seen a striking example of its truth. The patient was gradually recovering from inflammation of the chest, for the cure of which low diet was for a time indispensable. By way of supporting the diminished strength, the relations began to give prematurely and clandestinely, about double the quantity of food which was prescribed. For twenty-four hours, an increase of strength was felt accordingly; but very soon it passed into febrile excitement with a quick pulse and increased weakness. A dangerous relapse followed, and its cause was then found out. Abstinence was again enforced and tartar emetic given to excite nausea. To the surprise of the very injudicious friends, the excitement began almost immediately to subside and the strength to improve where they had just seen it fast giving way under a full diet.
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.
But the most common source 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; just as the dog already mentioned ate till the œsophagus was distended, although it did not experience the slightest sensation of hunger.[11] In fact, the whole science of a skilful cook is expended 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 occurrence 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, and in our habitual neglect of its dictates. When we attend to its real indications, 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 embitter 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 would be digested with ease if introduced into the stomach. Esquirol alludes to cases of this description, and I have met with similar examples. Voison also mentions, that, in the Hospital of Incurables in Paris, there are some 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, or 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 pounds 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 merely a 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 channel—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 in summer, in warm climates, and in persons engaged in severe exertion, particularly if exposed at the same time to a heated atmosphere. Blacksmiths, glass-blowers, 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. For the same reason great loss of blood induces excessive and intolerable thirst; and hence, in the battle-field, the generous self-denial of him who passed the cup to his wounded neighbour, without stopping even to moisten his own lips, cannot be too highly appreciated.
Thirst varies in intensity also according to the nature of the 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 circumstances 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 drink too much wine. In instances of this kind I have heard great thirst in the evening and during the night complained of as habitual, without the person even suspecting that it was owing to the wine; and yet, on abstaining from the latter, the thirst very soon disappeared.