THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 103 
Feeding. Fasting. 
1st | 2d | 3d | 4th} 5th | 1st | 2d | 3d 
Day.| Day.| Day.| Day. | Day.| Day. | Day. | Day. 
From food of Ist day of feeding.. .-| 80) 13) 5 | 2 
[73 “ 
[<9 “ce ce a ce ce ce 80 = a 2 
‘ “ Ath © “ ay a ce i 2 
“ “cc ee 5th ce “ee ce 80 13 5 2 
Total........ 80 | 93 | 98 |100 |100 | 20 | 7| 2 
On the above assumptions, theré remained in the body at the 
end of the first day 20 grams of nitrogen in the form of unmeta- 
bolized proteids. At the end of the second day this had increased 
to 27 grams, and at the end of the third day had reached the maxi- 
mum of 29 grams. At the end of the first day’s fasting it had fallen 
to 9 grams, at the end of the second day to 2 grams, and at the end 
of the third day to zero. In other words, the transitory storage 
of proteids observed by Voit and others is explained by Gruber as 
due to the fact that the nitrogen cleavage extends over more than 
a single day. 
In reality, of course, the excretion does not take place with any 
such mathematical exactness as in this schematic example, and 
after long fasting in particular a certain rebuilding of proteid tissue 
may occur, but the assumed figures may serve to give a general 
notion of the relations of food-supply and excretion. 
In brief, then, we may suppose that when proteid food is given 
to a fasting animal the stimulating effect upon the nitrogen cleavage 
anticipates the use of the proteids for constructive purposes and 
that a large proportion of them is thus destroyed as proteids before 
it can be used to make good the loss of proteids by the organized 
tissues. In other words, the proteids actually available for the 
tissues are much less than the amount supplied in the food. In 
this view of the matter we can readily see why the proteid supply 
overtakes the nitrogen excretion so slowly and why two or three 
times the amount metabolized in fasting is necessary to make good 
the loss from the body and ensure nitrogen equilibrium. 
