102 PRINCIPLES OF ANIMAL NUTRITION. 
at first and the fall, rapid at first, and then very gradual, until the 
minimum of the fasting excretion is reached about the third day. 
On the other hand, Rjasantzeff * and Shepski} ascribe the in- 
crease in the nitrogen cleavage after a meal to the increase in the 
digestive work rather than to the proteids as such. They find it 
possible, by stimulating the activity of the digestive organs without 
introducing food, to considerably increase the nitrogen excretion 
in the urine, while, on the other hand, the introduction of proteid 
food through a gastric fistula produced little or no effect. They 
also find the increase with the same amount of food nitrogen to be 
proportional to the (estimated?) amount of digestive work, but seem 
to offer no explanation of the equality of nitrogen cleavage and 
nitrogen supply. 
Cause or TraNnsiTory SroraGe.—As already noted (p. 96), 
any change in the rate of proteid supply in the food, while resulting 
ultimately in a corresponding change in the rate of nitrogen excre- 
tion, gives rise to a transitory gain or loss of nitrogen by the body, 
which was interpreted by Voit as consisting in a corresponding 
change in the stock of “circulatory protein” in the body. The 
facts which we have just been considering permit us to trace some- 
what more fully the details of the phenomenon. Gruber points 
out that while the larger part of the nitrogen cleavage consequent 
upon a single meal of proteids takes place within a few hours, the 
remainder is prolonged over two or three days, as in the case illus- 
trated above, while he likewise shows experimentally that this 
effect is not due to a retention of the nitrogenous metabolic prod- 
ucts, but represents the actual course of nitrogen cleavage. 
Such being the case, the transitory gain or loss incident to a’ 
change in the rate of proteid supply is most simply explained as 
the result of a superposition of the daily curves. Let it be assumed, 
for example, that 80 per cent. of the nitrogen cleavage incident to 
a single meal of proteids takes place on the first day, 13 per cent. 
on the second, 5 per cent. on the third, and 2 per cent. on the fourth. 
Then if we give to a fasting animal an amount of proteids contain- 
ing 100 grams of nitrogen for five successive days and then with- 
draw the food, the food nitrogen will be excreted as follows on the 
several days: 
* Jahr. Thier Chem., 26, 349. ft Ibid., 30, 711. 
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