22 PRINCIPLES OF ANIMAL NUTRITION. 
upon the dextrose as one of the products of the metabolism of 
those cells. 
Since, however, the demands of the organism for dextrose and 
the supply of it, or of the materials for its manufacture, in the food 
do not keep pace with each other, sometimes one and sometimes the 
other being in excess, the liver has a second function. When the 
food-supply, of whatever kind, is in excess, instead of continuing to 
produce dextrose the metabolism in the liver takes a slightly differ- 
ent form and produces the insoluble glycogen, or perhaps the dex- 
trose of the portal blood is simply converted into glycogen without 
entering into the structure of the hepatic vrotaplasm. When, on 
the other hand, the food-supply is deficient, the stored-up glyco- 
gen is converted into dextrose; whether by some sort of enzyme 
action or by again serving as food for the hepatic protoplasm is 
uncertain. 
Fate of the Dezxtrose of the Blood. 
The fact that the proportion of dextrose in the blood is approxi- 
mately constant, notwithstanding the continual supply which is 
received from the liver, shows that there must be a continual abstrac- 
tion of dextrose from the blood, which is as continually made good 
by the activity of the hepatic cells. In fact, the dextrose of the 
blood appears to play a very prominent part in the animal economy, 
and the function of the liver in preparing it from other ingredients 
of the food is a most important one. 
CoNSUMPTION IN THE MuscLEes.—From the point where it leaves 
the liver, our knowledge of the metabolism of the dextrose of the 
blood is scanty, but a large proportion of it undoubtedly takes 
place in the muscles. It was early shown by Chauveau that 
the proportion of dextrose in the blood diminishes in its passage 
through the capillaries of the body, so that the arterial blood con- 
tains more of this substance than the venous. In conjunction with 
Kaufmann * he has subsequently shown more specifically that in its 
passage through the muscular capillaries and through those of the 
parotid gland the blood is impoverished in dextrose, and to a much 
greater extent in the active than in the quiescent muscle. Coin- 
* Comptes rend., 108, 974 and 1057; 104, 1126 and 1352. 
