114 PRINCIPLES OF ANIMAL NUTRITION. 
for example) are employed to supply a part of the necessary energy, 
a more abundant fat production may be caused but the results 
are ambiguous, since it is possible that the non-nitrogenous residue 
of the proteids may be metabolized to furnish energy otherwise 
supplied by the non-nitrogenous nutrients and that the actual 
material for the formation of fat may come from the latter. 
That proteids added to a mixed ration may give rise to a large 
amount of fat has been strikingly shown by Kellner * in experi- 
ments on oxen in which wheat gluten was added to a fattening 
ration. Approximately 198 grams of fat were produced for each 
kilogram of protein fed, but to the writer the reasoning by which 
Kellner seeks to prove that this fat must have been derived directly 
from the proteids seems inconclusive. 
Finally, as was indicated in Chapter II (p. 50), the apparently 
well-established fact that the metabolism of proteids in the body 
gives rise to the formation of carbohydrates (or at least may do so), 
together with the further fact that fat is undoubtedly formed from 
carbohydrates, renders it difficult to assign any reason why the non- 
nitrogenous residue of the proteids should not supply material to 
the cells of the adipose tissue for the production of fat. 
§ 2. The Non-nitrogenous Nutrients. 
Effects on the Proteid Metabolism. 
The relations between proteid metabolism and proteid supply 
which have been outlined in the preceding section, while deduced 
mainly from experiments in which the food consisted substantially 
of proteids only, are of general applicability, yet are subject to im- 
portant modifications in the presence of non-nitrogenous nutrients. 
Tend to Diminish Proteid Metabolism.—As was first shown 
by C. Voit, the addition of non-nitrogenous nutrients to a ration 
consisting of proteids tends to render the prateid metabolism less 
than it otherwise would be. The effect is common to the fats and 
carbohydrates, although with some differences in details. 
Fars.—The following example, taken from Voit’s experiments,t 
illustrates in a somewhat marked way the influence of the addition 
of fat to proteid food upon the excretion of nitrogen. A dog con- 
suming daily 1000 grams of lean meat received in addition on two 
days 100 and 300 grams of fat, with the following results: 
* Landw. Vers. Stat., 53, 456. 
{ Zeit. f. Biol., 5, 334. 
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