66 PRINCIPLES OF ANIMAL NUTRITION. 
Ko6hler’s averages for dry, fat-free flesh are: 
CarbOts.ce dug Baie alaeuigetehe 52.60 per cent. 
Nitroreiiscc cis yeh hte Gas siepiteeets 16.67 “ “ 
Guiycocen.—Of the substances other than ash, fat and protein, 
which are found in the animal body, only glycogen calls for special 
mention here. This body, as we have seen, may be stored up in 
considerable amounts in the liver, and is found also in the muscles, 
although not in large proportion, except in case of the horse. In 
the aggregate, however, the store of glycogen in the body is not 
inconsiderable, having been estimated to be in the neighborhood 
of 300 grams in the human body. Moreover, changes of food or 
conditions, as well as muscular activity, may materially alter the 
store of glycogen and thus, perhaps, appreciably affect the make- 
up of the schematic body. 
So far as appears, however, the capacity of the body to store up 
glycogen is limited, as is indicated by the relatively small amount 
of it formed after even the most abundant feeding, and we may 
fairly assume that, at least on a ration equal to or exceeding the 
maintenance requirements, no long-continued change in the amount 
of glycogen in the body is likely to occur. 
SummMary.—We may sum up the foregoing paragraphs in the 
brief statement that for the purpose of investigating the statistics 
of nutrition we may consider the organic part of the animal body 
as composed essentially of fat and protein, with small amounts of 
glycogen, and that we may regard the permanent effect of a ration 
upon the body as consisting (aside from its effect on the ash ingre- 
dients) in an increase or decrease of its stores of fat and protein, 
these substances having the average compositon indicated above. 
The Gain or Loss of Protein.—Since the term protein as here 
used is synonymous with total nitrogenous matter, the gain or loss 
of protein by the body is necessarily indicated by its gain or loss of 
nitrogen. 
The supply of nitrogen to the body is contained in the pro- 
tein of the food. The losses of nitrogen from the body are 
contained— 
First, in that part of the protein of the food which fails of 
digestion and is excreted in the feces. 
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