DIGESTION OF FOOD. 359 
portance. It is as yet more of an art than a science; the cook 
has outstripped the physiologist, if not the chemist also, in this 
direction. i 
We can not explain fully why food prepared by certain 
methods and served in courses of a certain established order is 
so suited to refined man. A part is known, but a great deal 
remains to be discovered. We may, however, notice a few 
points of importance in regard to the preparation of food. © 
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 diet which not only imitates 
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. 
But all these instances are simple as compared with man. 
The lower mammals can live and flourish with comparatively 
little change of diet; not so man. He demands diet not only 
dissimilar in its actual grosser nature, but differently prepared. 
In a word, for the efferent nervous impulses, on which the 
digestive processes depend to be properly supplied, it has be- 
come necessary that a variety of afferent impulses (through 
eye, ear, nose, palate) reach the nervous centers, attuning them 
to harmony, so that they shall act, yet not interfere with one . 
another. 
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, 
