360 ANIMAL PHYSIOLOGY. 
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 
gelatine, albumin, and fats. Salt meat furnishes less nutri- 
ment, a large part having been removed by the brine; not- 
withstanding, all persons at times,.and some frequently, find 
such food highly beneficial, the effect being doubtless not con- 
fined to the alimentary tract. 
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 dogs it is both physiological and economical to 
give the animal the broth as well as the meat itself. The poor 
man may get excellent food cheaply by using not alone the 
meat of the shank of beef, but the extractives derived from it. 
There is much waste not only by the consumption of more food 
than is necessary, but by the purchase of kinds in which that 
important class of bodies, the proteids, comes at too high a 
price. 
It is remarkable in the highest degree that man’s appetite, 
or the instinctive choice of food, has proved wiser than our 
science. It would be impossible even yet to match, by calcula- 
tions based on any data we can obtain, a diet for each man equal 
upon the whole to what his instincts prompt. "With the lower 
mammals we can prescribe with greater success. At the same 
time chemical and physiological science can lay down general 
principles based on actual experience, which may serve to cor- 
rect some artificialities acquired by perseverance in habits that 
were not based on the true instincts of a sound body and a 
healthy mental and moral nature; for the influence of the 
latter can not be safely ignored even in such discussions as the 
present. These remarks, however, are meant to be suggestive 
rather than exhaustive. 
We may with advantage inquire into the nature of hunger 
and thirst. These, as we know, are safe guides usually in eat- 
ing and drinking. 
After a long walk on a warm day one feels thirsty, the 
mouth is usually dry; at all events, moistening the mouth, 
especially the back of it (pharynx), will of itself partially re- 
lieve thirst. But if we remain quiet for a little time the thirst 
grows less, even if no fluid be taken. The dryness has been 
