Another important principle, which Dr Beaumont conceives to be established by his numerous experiments, and which forced itself upon him by degrees, is, that in health THE GASTRIC SECRETION ALWAYS BEARS A DIRECT RELATION TO THE QUANTITY OF ALIMENT NATURALLY REQUIRED BY THE SYSTEM; so that, if more than this be taken, there will necessarily be too small a supply of the juice for the digestion of the whole. The principle here laid down is in perfect harmony with the sympathy which we have seen to exist between the stomach and the rest of the body, and therefore not only is highly probable in itself, but, if sound, will prove a most valuable guide in the practical regulation of diet. The number of phenomena which it explains, and its general applicability to daily use, afford no small presumption of its truth. When, for example, we eat more than the wants of the system require, indigestion will follow, because there will be more food in the stomach than what the quantity of gastric juice provided is able to dissolve; the proportion of the juice secreted being in relation, not to what we eat, but to the actual wants of the system, which, in the case supposed we have greatly exceeded. Here a remarkable harmony will be perceived between the quantity of the secretion and the true indications and uses of appetite as a guide to diet, explained in a preceding chapter (p. [21]).
The gastric secretion, and the appearance of the villous coat, undergo great modifications during disease, and on this subject also Dr Beaumont’s observations are highly valuable; because, instead of merely inferring, as others are obliged to do, he enjoyed the privilege of SEEING with his eyes what was actually going on. In the course of his attendance on St Martin, he found that, whenever a feverish state was induced, whether from obstructed perspiration, from undue excitement by stimulating liquors, from overloading the stomach, or from fear, anger, or other mental emotion depressing or disturbing the nervous system, the villous coat became sometimes red and dry, and at other times pale and moist, and lost altogether its smooth and healthy appearance. As a necessary consequence, the usual secretions became vitiated, impaired, or entirely suppressed; and the follicles from which, in health, the mucus which protects the tender surface of the villous coat is poured out, became flat and flaccid, and no longer yielded their usual bland secretion. The nervous and vascular papillæ, thus deprived of their defensive shield, were then subjected to undue irritation. When these diseased appearances were considerable, the system sympathized, and dryness of the mouth, thirst, quickened pulse, and other symptoms, shewed themselves; and NO GASTRIC JUICE COULD BE PROCURED OR EXTRACTED EVEN ON THE APPLICATION OF THE USUAL STIMULUS OF FOOD.
These facts, if correctly observed, are of extreme importance; and from the care with which Dr Beaumont pursued his investigations, and their accordance with the facts recorded by preceding physiologists, I do not think their general accuracy can be called in question. The dry irritated appearance of the villous coat, and the absence of the healthy gastric secretion in the febrile state, not only explain at once the want of appetite, nausea, and uneasiness generally felt in the region of the stomach, but shew the folly of attempting to sustain strength, by forcing the patient to eat when food cannot be digested, and when Nature instinctively refuses to receive it.
Before dismissing this part of the subject, it may be remarked, that the alleged sympathy of the stomach with the wants of the body has been denied, because the sense of hunger disappears the moment food is swallowed, or the stomach is distended even with clay or saw-dust, although the actual wants of the system cannot by possibility have been supplied in either case. But these facts seem to me rather to justify the inference that a sympathy does exist. Hunger ceases when food is taken, simply because now the condition of the stomach is in the desired relation to the state of the body, and the nerves consequently feel and transmit this impression to the more distant parts. In the other case, again, it ceases because the stomach cannot at first distinguish what is food from what is not; and, therefore, when distended, expresses content, because it feels satisfied that it has been honestly dealt with, and got what it wanted. But whenever it discovers the cheat, which it does in no long time, hunger returns, and can be properly appeased only by digestible substances. Dr Beaumont indeed expressly mentions, that, although the gastric secretion commences the moment any indigestible body touches the mucous surface of the stomach, it invariably ceases soon after discovering that the substance is one over which it has no power,—thus strongly confirming the existence of the sympathy. Here it may be also proper to observe, that from the frequent and pointed references which I have made to the results obtained by Dr Beaumont, some of my readers have imagined that I claimed for him the merit of the original discovery of all the truths which his experiments tend to establish. Nothing, however, was farther from my intention, and accordingly on page [87] I speak distinctly of his having eagerly embraced the opportunity afforded him of “testing the prevailing doctrines” on digestion; and on page [93] and other places I state that the same results had previously been arrived at by Tiedemann and other observers, but that the evidence in their favour adduced by Dr Beaumont was “more direct and incontrovertible,” and therefore more conclusive than their’s,—a position wholly at variance with any claim of discovery on his part. Indeed, the utter absence of pretension in Dr Beaumont’s work is one of its most pleasing characteristics.
CHAPTER V.
THEORY AND LAWS OF DIGESTION.
Different theories of Digestion—Concoction—Fermentation—Putrefaction—Trituration—Chemical solution—Conditions or laws of digestion—Influence of gastric juice—Experiments illustrative of its solvent power—Its mode of action on different kinds of aliment—beef, milk, eggs, soups, &c.—Influence of temperature—Heat of about 100° essential to digestion—Gentle and continued agitation necessary—Action of stomach in admitting food—Uses of its muscular motion—Gastric juice acts not only on the surface of the mass, but on every particle which it touches—Digestibility of different kinds of food—Table of results—Animal food most digestible—Farinaceous next—Vegetables and soups least digestible—Organs of digestion simple in proportion to concentration of nutriment—Digestibility depends on adaptation of food to gastric juice more than an analogy of composition—Illustrations—No increase of temperature during digestion—Dr Beaumont’s summary of inferences.
Before entering upon the consideration of the theory of digestion which naturally evolves itself from the facts expounded in the preceding chapter, it may be of advantage to turn for a moment to the various theories which have prevailed since the subject first attracted the attention of the learned.
Hippocrates regarded digestion as a kind of concoction or stewing; and many of his followers believed that it is effected in the stomach by the agency of heat alone, much in the same way as food is cooked over a fire. It is quite ascertained that heat favours the process, but it is pure absurdity to maintain that that agent alone will accomplish digestion.
Others of the older physiologists contended, that chymification results from simple fermentation of the alimentary mass, and referred to the gas disengaged during difficult digestion, as a proof that the process of fermentation goes on. But it is now demonstrated, that the tendency of healthy digestion is rather to arrest than to induce fermentation, and that the latter takes place only when disease exists, or when more food has been swallowed than the quantity of gastric juice secreted by the stomach is able to dissolve. Moreover, the products of digestion and of fermentation are so extremely different, that it is impossible to believe them to originate from the same chemical action.