128 PRINCIPLES OF ANIMAL NUTRITION. 
Subsequent investigations have substantially confirmed this 
conclusion. Thus Kayser * in an experiment upon himself found 
that the replacements of the carbohydrates of his diet by an amount 
of fat equivalent to them in heat value caused a marked increase 
in the urinary nitrogen, resulting in a loss of this element by the 
body in place of the previous small gain. The possible effect upon 
the apparent digestibility of the proteids of the food does not appear 
to have been considered. 
Wicke & Weiske + report two series of experiments upon sheep 
in which equivalent (“isodynamic’’) quantities of fat and of starch 
were added to a basal ration. In the first series the basal ration 
was comparatively poor in proteids and fat, having a nutritive ratio 
of about 1:8.3; in the second series it was richer in both these 
substances and had a nutritive ratio of 1:5.1 and 1:6.3 for the 
two animals respectively. As is usually the case, the starch dimin- 
ished the apparent digestibility of the protein of the basal ration, 
while the fat produced but a slight effect in this direction. Not- 
withstanding this complication, however, the effect of the starch 
in diminishing the proteid metabolism was clearly greater than 
that of the fat, and if the results were corrected for the increase 
in the nitrogenous metabolic products in the feces they would be 
still more decisive. 
The investigations of E. Voit & Korkunoff upon the minimum 
of proteids, which will be considered in a subsequent paragraph, 
also show a superiority in this respect of the carbohydrates over 
the fats which these authors ascribe to the greater lability of 
their molecular structure which enables them to enter into reactions 
in the body more readily than the fats. 
Magnitude and Duration of the Effect.—The pre-eminent 
position of the proteids in nutrition has perhaps led investigators 
to attach undue importance to this power of the non-nitrogenous 
nutrients to diminish the proteid metabolism. It is well to note 
that it is relatively small. C. Voit, as already stated, found an 
average decrease of about 7 per cent. with fats and about 9 per 
cent. with carbohydrates, and subsequent investigators have ob- 
tained results entirely comparable with these. 
PROTEID METABOLISM DETERMINED BY SuPPLy.—In the presence 
* vy. Noorden, Pathologie des Stoffwechsels, p. 117. 
+Zeit. physiol. Chem., 21, 42; 22, 137. 
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