Page images
PDF
EPUB

first, then, in being nitrogenised or azotised.

These last, even in vegetables, being identical in composition with the animal tissues, can be applied directly in the form of nutriment; the former must undergo certain changes to do so, or are employed for other purposes in the animal economy.

Now it is found that (generally speaking) the saccharine and oleaginous groups of elementary substances alone will not long support life in the higher orders of animals. These, however, are the elements which supply materials for the process of respiration, that is, they combine with the oxygen of the atmosphere, and the combustion which thus takes place generates the supply of animal heat. The albuminous group, on the other hand, is that which supplies directly the very materials of the animal structure to repair the waste continually going on in the body, being composed of precisely the same elements, whether derived from animal food or from the grain or seed of vegetables. It is truly remarkable that the only natural compound affording food in which ingredients from the three classes, gelatinous, albuminous, and saccharine, are combined, is milk. The gelatinous matter which enters so largely into the structure of the animal body, it appears may be formed out of the albuminous portion; but gelatinous food, though it will afford nutriment to the gelatinous portions of the body, will not do so to the albuminous, or in other words is not reconvertible into albumen: hence such articles of food as those soups, jellies, &c., which are composed chiefly of gelatine, will not alone support life for any length of time, but must be combined with other kinds containing albumen.

This brief sketch will introduce our readers to the following view of the actual results of the nutritive economy of animals, so well expressed by our author.

"The nutrition of the carnivorous races may, then, be thus described. The bodies of the animals upon which they feed contain flesh, fat, &c., in nearly the same proportion as their own; and all, or nearly all, the aliment they consume, goes to supply the waste in the fabric of their own bodies, being converted into its various forms of tissue. VOL. XXII.-No. 129,

After having remained in this condition for a certain time, varying according to the use that is made of them, these tissues undergo another metamorphosis, which ends in restoring them to the condition of inorganic matter; and thus give back to the mineral world the materials which were drawn from it by plants. Of these materials, part are burned off, as it were, within the body, by union with the oxygen of the air, taken in through the lungs; and they are discharged from these organs in the form of carbonic acid and water; the remainder are carried off in the liquid form by other channels. Hence we may briefly express the destination of their food in the following manner :—

[blocks in formation]

"But in regard to the herbivorous animals, the case is different. They perspire much more abundantly, and their temperature is thus continually kept down (chap. viii.). They consequently require a more active combustion, to develope sufficient bodily heat; and the materials for this are supplied, as we have seen, by the non-azotised portions of their food, rather than by the metamorphosis of their own tissues, which takes place with much less rapidity than in the carnivorous tribes. Hence we may thus express the destination of this part of their food; that of the azotised matter, here much smaller in amount, will be the same as in the preceding case.

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors]
« PreviousContinue »