NATURE AND DESTINATION OF THE FOOD OF ANIMALS. 323 



heat which it thus enables the animal body to maintain. This temperature, in 

 Carnivorous animals, appears to be sufficiently kept up by the combustion of 

 the carbon and hydrogen, set free by the decay (or metamorphosis, as it may be 

 termed,) of their tissues ; but this combustion goes on with much more rapidity, 

 in consequence of their almost unceasing activity, than it does in the Herbi- 

 vorous animals, which lead comparatively inactive lives. Every one who has 

 visited a menagerie must have noticed the continual restlessness of the Tigers, 

 Leopards, Hyaenas, &c., which keep pacing from one end of their narrow 

 cages to the other ; and it would seem as if this restlessness were a natural 

 instinct, impelling them to use muscular exertion sufficient for the metamor- 

 phosis of an adequate amount of -tissue, that enough carbon and hydrogen may 

 be set free for the support of the respiratory process. And we see a corre- 

 sponding activity in the Human hunters of the swift-footed Antelope and agile 

 Deer, which answers a similar purpose ; and which is remarkably contrasted 

 with the stupid inertness of the inhabitants of the frigid zone, which is only 

 occasionally interrupted by the necessity of securing the supplies of food 

 afforded by the massive tenants of their seas. The nutrition of the Carnivo- 

 rous 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. 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 inorganic matter ; and thus 

 give back to the Mineral world the materials which were drawn off 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 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 : 



Food consisting of"} c T . . ^ A , .,. fCarbonic acid and water 



albumen, fibrin, and 1 Convert- S J^JgL ( metamor- J thrown off b ? respiration. 

 other azotized com- \ ed into 1 ^e. Cph ose T?ntb 1 Urea and biliar T matter > &c " 

 pounds J ^thrown off by other excretions. 



But in regard to the Herbivorous animals, the case is different. They per- 

 spire much more abundantly, and their temperature is thus continually kept 

 down. They consequently require ' a more active combustion, to develop 

 sufficient bodily heat ; and the materials for this are supplied, as we have 

 seen, by the non-azotized portions of their food, rather than by the metamor- 

 phosis 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 azotized matter, here much smaller in amount, 

 will be the same as in the preceding case. 



Starch, oil, and J partly I Fatty and"^ but chiefly CCarbonic acid and Water, dis- 

 other non-azotized > converted < other an i- > th ro wn off< engaged by the respiratory 

 compounds ) into f mal tissues^ directly as (^process. 



The proportion of v the food deposited as fat, will depend in part upon the 

 surplus which remains, after the necessary supply of materials has been 

 afforded to the respiratory process. Hence, the same quantity of food being 

 taken, the quantity of fat will be increased by causes that check the perspira- 

 tion, and otherwise prevent the temperature of the body from being lowered, 

 so that there is need of less combustion within the body to keep up its heat. 



