Page:Popular Science Monthly Volume 1.djvu/321

Rh of this essay of the learned Bavarian physiologist. As the subject is important, we give a verbatim statement of the results.

Vegetable food, it is well known, contains, as its essential nutritive elements, albuminates, or nitrogenous materials, fatty matter, and hydrates of carbon, with water and nutritive salts. Such food, therefore, has the same elements as animal food; but in point of digestibility the two differ widely. Thus, while the carnivorous animal, when fed with sufficient flesh-meat, passes but little excrementitious matter, while it traverses the entire intestinal tract within eighteen hours after a meal; the herbivorous animal, on the contrary, when fed abundantly with vegetable substances, often retains the food in the intestine a whole week; and a considerable portion of this food remains unused. The proportion which the solid excretions bear to the weight of the animal is, for a dog fed on meat, as 3 to 10,000; for man with mixed food, 5 to 10,000; and for the ox, as 60 to 10,000.

We must observe that this difference is not due solely to the varying digestibility of the substances compared. These substances, as found in the excreta of herbivorous animals, are not such as resist the action of the digestive fluids. Henneberg and Stohmann have shown that the proportion of such substances digested depends upon their respective proportions in the sum of the food consumed. This is one of the most important recent contributions to the physiology of digestion. What renders vegetable food harder to digest is the fact that the albuminoid substances, fatty matters, starch, etc., are there incased in a coating of cellulose, to break up which requires some time. On this account, the intestine of the herbivora is longer and more complicated than that of the carnivora. The latter digest but a small proportion of cellulose. The same holds good for man, except when he consumes young cellulose but little consolidated, as tender pulse, roots, or fruits. The cellulose of hay and grass is of such quality that the human digestive apparatus cannot extract any of their nutritive elements. In order that we may utilize them, they must first be transformed by herbivora into their own substance.

Albuminates, whether derived from the animal or from the vegetable kingdom, leave but little alimentary residue. If fat be added to the albuminates, this residue is increased in proportion to the amount of fatty matter, especially when the latter is in excess. The addition of sugar, no matter in what quantity, has not the same result, provided it does not cause a diarrhoea. Of sugar, but faint traces are to be found in the residuum. With starch it is quite different, even when it is made pulp by boiling.

Adolph Meyer has made some interesting experiments in this matter. A dog was given 1,000 parts of bread per day (536 dry matter) and with such food his excreta amounted to 70 parts of dry substance. The equivalent of the albumen in the bread was then given, in the shape of flesh-meat, its starch being replaced by the respiratory