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and this metamor


converted into

Urea and

tissue ;

other azo-


matter,&c. thrown off

first, then, in being nitrogenised or After having remained in this condition azotised.

for a certain time, varying according to These last, even in vegetables, being

the use that is made of them, these identical in composition with the

tissues undergo another metamorphosis, animal tissues, can be applied directly condition of inorganic matter; and thus

which ends in restoring them to the in the form of nutriment; the former

give back to the mineral world the mamust undergo certain changes to do

terials which were drawn from it by so, or are employed for other purposes plants. Of these materials, part are in the animal economy,

burned off, as it were, within the body, Now it is found that (generally by union with the oxygen of the air, speaking) the saccharine and oleagi- taken in through the lungs; and they nous groups of elementary substances are discharged from these organs in the alone will not long support life in the

form of carbonic acid and water ; the

remainder are carried off in the liquid higher orders of animals. These, however, are the elements which sup

form by other channels. Hence we may

briefly express the destination of their ply materials for the process of respi- food in the following manner :ration, that is, they combine with the oxygen of the atmosphere, and the

Carbonic combustion which thus takes place

acid and

Food congenerates the supply of animal heat.

thrown off

sisting of The albuminous group, on the other


by respirahand, is that which supplies directly fibrin,and organised

phosed the very materials of the animal struc

biliary ture to repair the waste continually pounds, going on in the body, being composed

by other of precisely the same elements, whe

Lexcretions. ther derived from animal food or from the grain or seed of vegetables. It is

“But in regard to the herbivorous

animals, the case is different. They truly remarkable that the only natural

perspire much more abundantly, and compound affording food in which in

their temperature is thus continually gredients from the three classes, gela- kept down (chap. viii.). They consetinous, albuminous, and saccharine, quently require a more active combusare combined, is milk. The gelati. tion, to develope sufficient bodily heat; nous matter which enters so largely and the materials for this are supplied, into the structure of the animal body,

as we have seen, by the non-azotised it appears may be formed out of the

portions of their food, rather than by albuminous portion; but gelatinous

the metamorphosis of their own tissues, food, though it will afford nutriment

which takes place with much less rapito the gelatinous portions of the body, Hence we may thus express the desti

dity than in the carnivorous tribes. will not do so to the albuminous, or in nation of this part of their food; that of other words is not reconvertible into the azotised matter, here much smaller albumen : hence such articles of food in amount, will be the same as in the as those soups, jellies, &c., which are preceding case. composed chiefly of gelatine, will not alone support life for any length of time, but must be combined with other

Fatty and


but chiefly kinds containing albumen.

other ani

ed by the This brief sketch will introduce our tised com

directly as pounds,

respirareaders to the following view of the actual results of the nutritive economy of animals, so well expressed by our The proportion of the food deposited author.

as fat will depend in part upon the

surplus which remains, after the neces“ The nutrition of the carnivorous

sary supply of materials has been races may, then, be thus described. afforded to the respiratory process. The bodies of the animals upon which Hence, the same quantity of food being they feed contain flesh, fat, &c., in taken, the quantity of fat will be innearly the same proportion as their creased by causes that check the perown; and all, or nearly all, the aliment spiration, and otherwise prevent the they consume, goes to supply the waste temperature of the body from being in the fabric of their own bodies, being lowered, so that there is need of less converted into its various forms of tissue. combustion within the body to keep Vol. XXII-No. 129,


Carbonic acid and

and other

converted into

thrown of disengag

mal tis. sues ;

tory process.

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