That this impaired activity of the other functions after a full meal is natural, and intentionally arranged by the Creator, is plain, both from its universality among all kinds of animals, and from the mode in which it is produced. Among the lower creatures, the sluggishness induced by eating increases in proportion to the degree in which they gorge themselves with food. The boa constrictor, after a plentiful repast, slumbers for a week; and the glutton of our own species, in similar circumstances, drops into a stertorous sleep of several hours. If active exertion immediately after a full meal be rendered compulsory by any external cause, such as the presence of danger urging to flight, the aliment often remains for hours in the stomach undigested. Again, the very distention of the stomach inseparable from a hearty meal, necessarily impairs the activity of several of the functions, by directly pressing upon the vessels which supply their organs with blood, and consequently diminishing the stimulus essential to their activity.
The obvious practical inference to be deduced from a consideration of the principle under discussion is, that rest of body and tranquillity of mind for a short time both before and after eating are necessary, and conducive to healthy digestion. If we have been engaged in severe and fatiguing bodily exertion, or anxious meditation, just before sitting down to a meal, the blood which was flowing copiously through the vessels of the muscles or the brain to keep up their unusual action, still continues to do so, because a sufficient interval has not elapsed to allow the excitement to subside, and a new distribution to take place towards the organs concerned in digestion. The consequence is, that the stomach does not receive blood enough to carry on its increased action, and furnish gastric juice with sufficient rapidity, or in sufficient quantity, to mix with the whole of the food; and that the nervous energy, already partially exhausted by over-excitement in the remoter organs, is imperfectly supplied to the stomach, the tone and action of which are thus so far impaired as to render it no longer able to carry on digestion with its usual success. Accordingly, when we are fatigued with mental or bodily labour, we are naturally impelled to seek repose before sitting down to table; and if we yield to this instinctive prompting, and refresh ourselves by a rest, we not only enjoy better what we eat, but also digest it with an ease and comfort unattainable by swallowing our food the moment our labour is at an end—and hence the wisdom and advantage of appropriating half an hour to any light occupation, such as dressing, before sitting down to dinner. If, however, we have previously been engaged only in very moderate exercise, an interval of repose is not required, because then there is no undue excitement elsewhere to retard the necessary flow of blood and nervous energy towards the internal organs.
The practical rule of avoiding serious exertion of mind or body immediately after eating, which is directly deducible from the physiological law above explained, has long been acted upon in our treatment of the lower animals; and no one who sets any value on the lives of his horses or dogs, ever allows it to be disregarded with respect to them. And yet the same man who would unhesitatingly dismiss his groom for feeding his horse immediately after a fatiguing chace or a gallop home, would probably think nothing of walking into the house and ordering dinner to be instantly served for himself in similar circumstances. In the army, the difficulty of managing recruits on a march, in this respect, has often been remarked. Fatigued with the day’s exertions, they are impatient for food, and, when they get it, can scarcely refrain so long from devouring it as to admit of its being even moderately cooked. They consequently labour under the double disadvantage of eating before the system is in a sufficient state of repose to benefit by the supply, and of having the food itself in a condition unfit for easy digestion. The old campaigner, on the other hand, instructed by former experience, restrains his appetite, systematically kindles his fire, cooks his victuals, and makes his arrangements for the night, with a coolness of deliberation which surprises the recruit; and he is amply repaid for his temporary self-denial, by the greater enjoyment and support which he derives from the very same materials which the impatience of the other has caused him in a great measure to waste.
Let any one who doubts the advantages resulting from attention to this rule, consider for a moment its universal and scrupulous observance by postmasters and jockies, and think whether these are persons likely to throw away time and trouble on a useless ceremony. When a horse is taken out of harness, an interval of repose is always allowed, that the excitement of the system may have time to subside; and then not only an eager appetite but an active digestion are sure to follow. Many a valuable horse has been killed by being prematurely fed after fatiguing exercise, and man himself is no exception to the rule. He not only enjoys a meal with superior relish, but digests it better, when due repose has removed the fatigue and excitement of exertion. Even after continued activity of mind, a period of tranquillity or of gentle bodily exercise is eminently conducive to the healthy action of the stomach, precisely because it favours the new distribution of the circulating blood which that process requires.
In accordance with this law of digestion, there is throughout the whole animal creation a marked aversion to activity for some time after a full meal, although man, eager in the pursuit of gain or the gratification of other passions, often sets it at defiance, and engages in bodily or mental labour both immediately before and after meals; but, in return, he receives his reward for despising the authority of Nature, in a severity of suffering from which the animals whom he treats so much better than himself are by his care entirely exempted. No where, for example, does man hurry off to business so immediately as in the United States of America, and no where does he bolt his food so much as if running a race against time. The consequence is, that no where do intemperate eating and dyspepsia prevail to the same enormous amount. Even in England, according to Dr Caldwell, the extent of transgression cannot be compared with what is witnessed among our Transatlantic brethren; and the result shews, that if we in Britain suffer from indulging our fondness for good things, the comparatively deliberate way in which we set about enjoying them serves as a partial safeguard, and exempts us from a portion of the punishment which our brethren bring down upon themselves, by the hurry with which they first devour their food and then set off to work. Rapid eating almost invariably leads to overloading the stomach; and when to this is added a total disregard of the quietude necessary for digestion, what can be expected to follow but inveterate dyspepsia?
The reason why wounds, bloodletting, bathing, and other circumstances which tend to disturb the regularity of the circulation, are so hurtful after a full meal, will now be apparent. The effect of wounds and bloodletting is to give rise to an instantaneous change in the distribution of the blood, and to deprive the stomach of that which is now doubly required. Bathing, whether hot or cold, has an analogous effect; and so, indeed, have all violent and sudden bodily or mental shocks.
It must not, however, be imagined that the period of repose necessary to insure healthy digestion extends over the whole time of the continuance of food in the stomach. After a moderate meal and in ordinary health, the concentration of the vital powers in that organ, and their proportionate depression in other parts of the body, rarely continue, at least in a very marked degree, beyond the period usually allotted to the siesta, or sleep after dinner, in warm climates, and even in Italy and Spain—namely, an hour or an hour and a half. When the meal has not exceeded the bounds of moderation, a sufficient quantity of gastric juice for the digestion of the whole is secreted generally within the first hour; after which time, consequently, the same quantity of blood is no longer required to be directed towards the stomach, but may beneficially be distributed to such other parts as from their activity more immediately require its aid. If the muscular system is to be employed in labour or locomotion, the blood can now be spared to sustain its activity; if the mind is to be engaged in intellectual pursuits, it can be sent to the brain without robbing the stomach. The same principle of course applies to all the other organs; and it is therefore chiefly during the first hour, till all the gastric juice be provided and the chymification of the food be fairly commenced, that tranquillity of mind and inaction of body are so essential.
As already mentioned, the reality of increased circulation in the vessels of the stomach during digestion has been established by ocular demonstration, as well as by analogy. The increase in the supply of nervous energy which takes place at the same time is, however, scarcely less certain, although from its nature incapable of being seen. It is the almost characteristic feature of the nervous system to be excited by stimulus to increased action; and we formerly saw that when the nerves of the stomach are cut, and the flow of nervous influence is arrested, digestion instantly suffers. But the same principle holds in the nervous as in the circulating system. Energetic action cannot be kept up in two distant parts of the body at the same time. If the intellect be intently occupied in profound and absorbing thought, the nervous energy will be concentrated in the brain, and any demands made on it by the stomach or muscles will be very imperfectly attended to. If, on the other hand, the stomach be actively engaged in digesting a full meal, and some subject of thought be then presented to the mind, considerable difficulty will be felt in pursuing it, and most probably both thought and digestion will be disturbed. If the mental effort required be easy and agreeable, and the meal be a very temperate one, there will be much less difficulty in simultaneously proceeding with both, because comparatively little nervous energy will then suffice for them. Still, however, each will go on more efficiently if not interfered with by the other.
When the mind is active and vigorous, and properly exercised in all its departments of feeling and affection as well as of intellect, the nervous influence which the brain produces is not only more abundant, but of a more healthful and invigorating quality. Hence the well-known preservative and restorative influence of cheerful dispositions and gratified activity of mind, and hence the depressing, morbid, and often fatal effects of corroding care, grief, and apprehension, on every organ of the body. Hence, too, the weak digestion and sallow complexions of literary men and hard students, who suffer severely from transgressing this law of the animal economy by habitually engaging in occupations requiring much exertion of mind, not only soon after, but even during the very act of swallowing their meals. Ignorant of the connexion subsisting between the different functions, and of their laws of action, few can be convinced in time of the importance of observing this condition, even after its operation has been explained to them. In the conclusion, however, experience teaches many whose reason is insufficient for their guidance, and forces them to a closer conformity with the dictates of nature, when obedience is almost too late to be of benefit.
The prodigious influence of the nervous system on digestion is familiarly and unequivocally exhibited in almost every case of dyspepsia which each succeeding day brings under the notice of the physician. He knows well from experience that the diet may be selected with every care, its quantity duly proportioned, and exercise rigidly practised, and yet all his curative treatment fail even to relieve, unless his patient be at the same time freed from the pressure of care, and due attention be devoted to the observance of mental and bodily repose after every meal. The heavier the meal the greater is the desire for absolute rest, and the less advantageously can active exertion be encountered. When the stomach is loaded, the whole vital energies seem to be concentrated in it to enable it to cope with the task imposed upon it. But when we eat temperately, there is less necessity for entire quietude of mind and body. Accordingly, if we do not experience the same dislike to exertion after a light forenoon lunch, which we do after a heavy late dinner, the reason is simply, that less gastric juice, less nervous energy, and less vigorous action in the stomach, are required to digest in the one case than in the other.