THE RELATIONS OF METABOLISM TO FOOD-S UPPLY, I01 
tion of normal physiological activity. It has been repeatedly 
demonstrated, however, that when the period of growth is past, the 
animal body has not the ability to produce any material amount of 
proteid tissue. A large supply of proteid food, then, necessarily 
tends to alter the composition of the blood and other fluids of the 
body, and the nitrogen cleavage is evidently an effort on the part 
of the organism to counteract this effect by splitting off from the 
proteids a nitrogenous group which can be rapidly excreted, leav- 
ing a non-nitrogenous residue which, so far as it is not immediately 
needed to supply energy, is capable of storage in the relatively inert 
and insoluble forms of glycogen and of fat. 
According to Rosemann,* the rapid increase in the nitrogen ex- 
cretion after a meal arises from two concurrent causes: first, a 
direct stimulus to the proteid metabolism, due to the rapid increase 
of proteids and their digestion products in the blood, which is 
somewhat transitory in character; and, second, the effect of a 
larger relative supply of proteids in causing, according to well- 
known physico-chemical laws, a relatively larger number of mole- 
cules of these substances to enter into reactions with the cell proto- 
plasm. The accompanying graphic representation by Gruber + of 
the course of the nitrogen excretion of a dog on the second day of 
5 fame N 
4 A 
/ 
a, \ 
~ 
0 2 4 6 8 10121416 18 2022 24 2 4 6 8 10121416 18202224 2 4 6 8 10121416 18202224 2 4 G6 8 10121416 18 20 22 24 
HOURS 
RATE OF NITROGEN EXCRETION PER TWO HOURS, 
. 
feeding with 1000 grams of lean meat and on the three following 
fasting days shows plainly the sudden stimulation of the excretion 
* — * Loe. cit. t Loe. cit., p. 421. 
