144 PRINCIPLES OF ANIMAL NUTRITION. 
the ill effects directly to the small supply of proteids, but some other 
writers appear inclined to explain them as due to the long continu- 
ance of a uniform and rather artificial diet. The writer’s experi- 
ments, cited above, showed no evidence of any ill effect in the case of 
cattle upon a ration containing but about 200 grams digestible pro- 
tein per day and continued for seventy days, and subsequent obser- 
vations, as well as the common experience of farmers in wintering 
cattle upon such feeding-stuffs as inferior hay, straw, etc., fully 
confirm this result. 
Effects on Total Metabolism. 
Substitution for Body Fat.—We have seen in the preceding 
section that proteid food, or rather the non-nitrogenous residue 
arising from its cleavage in the body, may be utilized as a source of 
energy in place of the body fat which would otherwise be meta- 
bolized. Similarly, the non-nitrogenous nutrients supplied in the 
food may be thus substituted for body fat in the metabolism of the 
animal. The substitution is shown most clearly in experiments 
upon fasting animals, although it appears also in those in which 
these nutrients are added to an insufficient ration. 
Fat.—The following averages of Pettenkofer & Voit’s experi- 
ments,* computed from Atwater & Langworthy’s digest,t illustrate 
this substitution of food fat for body fat: 
Gain or Loss by Body. 
Food, Number of 
Grms. Experiments. . 
Nitrogen, Fat, 
Qrms. Grms. 
Nothing 5 —6.64 — 97.76 
100 iat 2 —4.90 — 16.25 
350 “ 1 —7.70 +113.60 
The smaller amount of fat not only diminished the proteid meta- 
bolism but also largely reduced the loss of fat from the body. The 
larger amount of fat showed the tendency noted on p. 115 to increase 
the proteid metabolism, but at the same time it not only suspended 
the loss of body fat but caused a storage of fat in the organism. Of 
course we have no means of distinguishing in such a case between 
* Zeit. f. Biol., 5, 370. 
+ U.S. Dept. Agr., Office of Experiment Stations, Bull. 45. 
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