360 COMPARATIVE PHYSIOLOGY. 



common experience and to more exact experiments to ascertain 

 the best methods of feeding animals for fattening, for work, 

 or for breeding. ' Inferences drawn from the feeding habits of 

 wild animals allied to the tame to be valuable must always, 

 before being applied to the latter, be subjected to correction by 

 the results of experience. 



It is now well established by experience that animals kept 

 in confinement must have, in order to escape disease and attain 

 the best results on the whole, a die.t which not only iinitates 

 that of the corresponding wild forms generally, but even in 

 details, with, it may be, altered proportions or added constitu- 

 ents, in consequence of the difference in the environment. To 

 illustrate: poultry can not be kept healthy confined in a shed 

 without sand, gravel, old mortar, or some similar preparation ; 

 and for the best results they must have green food also, as 

 lettuce, cabbage, chopped green clover, grass, etc. They must 

 not be provided with as much food as if they had the exercise 

 afforded by running hither and thither over a large field. We 

 have chosen this case because it is not commonly recognized 

 that our domesticated birds have been so modified that special 

 study must be made of the environment in all cases if they are 

 not to degenerate. The facts in regard to horned cattle, horses, 

 and dogs are perhaps better known. 



Cooking greatly alters the chemical composition, the me- 

 chanical condition, and, in consequence, the flavor, the digesti- 

 bility, and the nutritive value of foods. To illustrate : meat in 

 its raw condition would present mechanical difficulties, the di- 

 gestive fluids permeating it less completely ; an obstacle, how- 

 ever, of far greater magnitude in the case of most vegetable 

 foods. By cooking certain chemical compounds are replaced 

 by others, while some may be wholly removed. As a rule, 

 boiling is not a good form of preparing meat, because it with- 

 draws not only salts of importance, but proteids and the ex- 

 tractives — nitrogenous and other. Beef-tea is valuable chiefly 

 because of these extractives, though it also contains a little 

 gelatin, albumin, and fats. 



Meat, according to the heat employed, may be so cooked as 

 to retain the greater part of its juices within it or the reverse. 

 With a high temperature (65° to 70° C.) the outside in roasting 

 may be so quickly hardened as to retain the juices. 



In feeding dog's it is both physiological and economical to 

 give the animal the broth as well as the meat itself. 



