3° PRINCIPLES OF ANIMAL NUTRITION. 
1. The animal body produces fat from other ingredients of its 
food. 
2. The carbohydrates and related bodies of the food serve as 
sources of fat. . , 
3. It is probable that the proteids also serve as sources of fat. 
So far, then, as that portion of the fat which is actually pro- 
duced in the body from other substances is concerned, we may most 
readily conceive of its formation as consisting essentially of a 
manufacture of fat by the protoplasm of the fat cells, which are 
nourished by the carbohydrates, proteids, and other materials 
brought to them by the circulation. 
Functions of the Food Fat.—The fat which is manufactured 
in the body from other ingredients of the food, however, often con- 
stitutes the larger portion of the total fat production, while but 
a relatively small proportion at most can be derived from the fat 
of the food. The question naturally arises whether this smaller 
portion contained in the food is simply deposited mechanically, so 
to speak, in the fat cells, or whether it too, like the carbohydrates 
and proteids, serves to nourish the fat cells and supply raw material 
out of which they may manufacture fat. 
At first thought the former alternative might seem more prob- 
able. The fat of the food, so far as we are able to trace it, does not 
undergo any considerable chemical changes, such as the proteids 
do, e.g., in the process of digestion, but is largely resorbed in the 
form of apparently unaltered fat. Moreover, resorption of fat takes 
place largely through the lacteals and the resorbed fat reaches the 
general circulation without being subjected like the carbohydrates 
to the action of the liver. 
Deposition oF Fore1cn Fars.—The view just indicated is 
supported to a considerable extent by the results of experiments 
upon the fate of foreign fats introduced into the body. 
Experiments by Radziejewsky * and Subbotin + were indecisive. 
but Lebedeff t was later successful in obtaining positive re- 
sults. Two dogs, after prolonged fasting. received small amounts 
of almost fat-free meat together with, in the one case, linseed oil, 
*Virchow’s Archiv., 56, 211; 48, 268. + Zeit. f. Biol.. 6, 73. 
} Thier. Chem. Ber., 12, 425; Zeit. Physiol. Chem.. 6, 149: Centralb]. med. 
Wiss., 1882, 129. 
