Digestion of Mineral Substances? 169 it has the effect of restoring moisture to the pharynx and œsophagus, and of mechanically favouring the solution of the contents of the stomach. Beer and wine have the additional effect of exciting the organ of taste to a keener relish of the flavour of food, and the stomach to increased energy of digestion. The quantity of aqueous liquid consumed during a meal depends upon habit, and in general is quite unimportant. But dyspeptic persons sometimes find it beneficial to abstain altogether from drinking at and for a short time after a meal. The solid substances taken into the stomach are derived from various sources. In the ordinary habits of civilized life, the deglutition of mineral substances is restricted to remedial agents that are taken in minute quantities; what changes they undergo, and by what means they are absorbed, is imperfectly known; their absorption is sufficiently proved by the effects which are produced upon the system. But there are instances of savages who consume daily large quantities of an unctuous earth; and although there is no evidence in this case that any part of the mineral element is absorbed, it is nevertheless possible that it may in some manner contribute to the purpose of nourishment. The aranea scenica, according to Mr. Holt, devours sulphate of zinc, and appears to deprive that salt of its acid. Plants seem interposed between the soil and animal life as laboratories for combining the elements of inert matter into substances capable of being assimilated in the digestion of animals: and animals differ among themselves in the original fitness of their organs for assimilating vegetable matter, so that some appear of an intermediate class in reference to the function of diges 170 Vegetable and Animal Principles employed as Food. tion, being intended to animalize vegetable matter, while they are themselves prepared by Nature to be the prey of carnivorous animals. Those which are herbivorous have the alimentary canal considerably more complicated than those which live on animal food; either the stomach is divided into distant chambers, or the colon and cæcum are remarkably developed to fit them for the more elaborate concoction of the food. The common food of human beings consists either of muscular flesh and fat, of milk and eggs, or of the seeds of certain grasses, of the roots, the leaves, and stalks of different vegetables, and of various kinds of fruit. But the former substances are found to be more nutritious than the latter; and the greatest bodily strength is attained by combining a diet composed chiefly of animal substance with habits of regular and violent exercise. The proximate principles of animal matter which serve for nutriment are fibrin, albumen, jelly, oil, and osmazome or the extractive matter of meat, which seems to give the specific flavour to the flesh of different animals, but may possibly consist of fibrin only, slightly altered by heat'. Gluten, farina, mucilage, oil and sugar, are the nutritive proximate principles of vegetable matter; at the head of which gluten is placed, as a substance containing nitrogen, and more resembling animal matter than any other proximate principle in plants. It appears that those animals whose nature it is to prefer one sort of food, either animal or vegetable, may gradually be brought to adopt the opposite: it is there * Thomson's Chemistry, vol. iv. p. 424. Variety of Diet useful. 171 fore less surprising that the digestive organs of man, which are placed between those of carnivorous and graminivorous animals, though coming nearer to the latter, should readily accommodate themselves to either kind of nutriment: but even in man the transition cannot be made abruptly without inconvenience. A person accustomed to a large proportion of animal food, on restricting his diet to vegetables is liable to suffer heartburn, a sense of weight and oppression at the stomach, with flatulence, and other symptoms of indigestion, and the bodily frame is rendered less capable of exertion. Yet occasional changes in diet Nature appears to prescribe: in hot weather the appetite is better pleased with fruits and a larger proportion of vegetable food; in cold weather we prefer the reverse: and the same distinction is observed in the habits of the different races of mankind which people the cold or the torrid regions of the globe. The mixture and variety of diet which the palate and appetite recommend, so far from being injurious to a healthy stomach, is in the highest degree beneficial to it, and serves to keep it in tone and vigour. The prejudicial nature of luxurious diet results from other circumstances; every stomach has its idiosyncrasy, and in a diversity of viands there are some calculated to derange the digestion of one, some of another; and no doubt a succession of savoury dishes is liable to tempt the appetite to unrestrained indulgence. But supposing a moderate discretion, which avoids such viands as are experimentally found to be unwholesome, and such excess as is palpably gross; and there is no question but good living, which presents alternately to the palate every va 172 Effects of restricting Diet riety of food, soliciting the appetite at one time to one class of viands, at another to a different class, alternately to plain and to highly-seasoned food, is more wholesome than a diet closely restricted to a few simple articles of food.' The perfection of bodily strength is not produced by application to one laborious employment: a vigorous state of the understanding does not result from its confinement to one pursuit; and the health of the digestive organs is promoted by following these analogies. Dr. Stark made himself the subject of a curious series of experiments upon the relative effects of various simple forms of diet when employed each for a short time exclusively. His researches are principally valuable as tending to show the debility and unwholesome state of body which may be brought on by this practice, and which in his own case led to an untimely death. Recently M. Majendie has furnished data for a similar conclusion to that suggested by the melancholy history of Dr. Stark, in a series of experiments set on foot to illustrate the unfitness of substances which contain no nitrogen for the nutriment of animals. A dog fed upon white sugar and water exclusively appeared for seven or eight days to thrive upon this sustenance. He was lively, ate and drank with avidity. Towards the second week he began, however, to lose flesh, though his appetite continued good. In the third week he lost his liveliness and appetite; and an ulcer formed on the middle of each cornea, which perforated it, and the humours of the eye escaped: the animal became more and more feeble and died the thirty-second day of the experiment. Results nearly similar ensued with dogs to a single Substance.. 173 fed upon olive oil and distilled water; but no ulceration of the cornea took place, and upon dogs fed with gum, and with butter. A dog fed with white bread made from pure wheat and with water died at the expiration of fifty days. Another, fed exclusively on military biscuit, suffered no alteration in its health. Rabbits or Guinea pigs fed upon one substance only, as corn, hay, barley, cabbage, carrots, &c. die with all the marks of inanition, generally in the first fortnight, and sometimes sooner. An ass fed upon boiled rice died in fifteen days, having latterly refused its nourishment. A cock lived for many months upon this substance, and preserved its health. Dogs fed exclusively with cheese, or with hard eggs, are found to live for a considerable period, but become feeble, meagre, and lose their hair. The substance from which rabbits and Guinea pigs can derive subsistence for the longest period appears to be muscular flesh. When a certain degree of emaciation has been produced by feeding an animal for some time upon one substance, as for instance upon white bread during forty days, the animal will yet eat with avidity different kinds of food offered to it at that period; but it does not regain its strength; it continues to waste, and dies about the same time at which its death would have happened had the exclusive diet been continued". Thus it appears that the selection of the most nutri "Majendie. Elémens de Physiologie, tome ii. p. 494. |