THE METABOLISM OF THE BODY. 457 
of man when feeding largely on a flesh diet, show that the pro- 
teid metabolism is under such circumstances very active. 
Itis also a well-known observation that carnivorous ani- 
mals (dogs) are more active and display to a greater extent 
their latent ferocity, evidence of their descent from wild car- 
nivorous progenitors, when like them they feed very largely on 
flesh. The evidence seems to point pretty clearly to the con- 
clusion that a nitrogenous (flesh) diet increases the activity of 
the vital processes of the body, and especially the proteid me- 
tabolism. ’ 
Some have explained this result on the assumption that 
such diet led to an increase in the red corpuscles of the blood, 
and hence in the oxygen-supply ; but mere abundance of sup- 
ply will never of itself explain results in a living organism. It 
may be and probably is true that such a diet augments the 
activity of the oxidative processes, but the reason of this lies 
deeper, we think, than the explanations as yet offered assume. 
That an excess of proteids may be stored, as it seems, is true of 
fats and carbohydrates, to be used in the hour of need, seems 
not improbable, though this has not as yet been shown to be 
the case. But in all these considerations it must be borne in 
mind that the metabolic processes go on in the tissues and not 
in the blood, and probably not in the lymph. Not that these 
fluids (tissues) are without their own metabolic processes for 
and hy themselves; but what is meant to be conveyed is that 
the metabolic processes of the body generally do not take place 
in the blood. 
The Effects of Gelatine in the Diet— Actual experiment shows 
that this substance can not take the place of proteid, though it 
also makes it evident that less of the latter suffices when mixed 
with a certain proportion of gelatine; and it has been suggested 
that it is split up into a fatty portion and urea, and that it thus, 
by aiding in the formation of fat, preserves some of the proteid 
for other uses than fat construction. This theory, however, is 
not well substantiated. It will be borne in mind that ordinary 
flesh contains, as we find it naturally in the carcass, not only 
some fat, but a good deal of fibrous tissue, which can be con- 
verted by heating into gelatine. 
Fats and Carbohydrates.—It is a matter of common observa- 
tion and of more exact experiment that even a carnivorous ani- 
mal thrives better on a diet of fat and lean meat than on lean 
flesh alone. Thus, it has been found that nitrogenous equi- 
librium was as readily established by a due mixture of fat and 
