METABOLISM. 19 
circulation again through the hepatic vein. In its passage through 
the capillaries of the liver, the blood is subjected to the action of the 
cells of the liver (hepatic cells); Our knowledge of the exact nature 
of this action is still more or less conjectural, in spite of a vast 
amount of experimental investigation, but certain general facts are 
pretty clearly established. 
In the first place, the hepatic cells appear to serve as a source of 
dextrose when no carbohydrates are supplied in the food. If a 
carnivorous animal be given a diet as free as possible from carbo- 
hydrates, as, for instance, prepared lean meat, consisting substan- 
tially of proteids, its blood still contains a normal amount of dex- 
trose and the blood in the hepatic vein is found to be richer in 
dextrose than that of the portal vein, showing that this substance 
is being formed in the liver. Moreover, while the percentage of 
dextrose in the blood is small, the total amount thus manufactured 
is very considerable. Seegen * estimates it at about one per cent. 
of the weight of the body in twenty-four hours. This is regarded 
by many physiologists as an overestimate, the considerable differ- 
ences in sugar content between the portal and hepatic blood found 
by Seegen being regarded as in part the effect of the necessary 
operation. Indeed, it is questioned by some whether any actual 
difference in sugar content between the portal and hepatic blood 
under normal conditions has been satisfactorily established analyti- 
cally, but the indirect evidence at least seems strongly in its favor. 
In the second place, the same outflow of dextrose from the liver 
appears to take place when the animal consumes a mixed diet con- 
taining carbohydrates. In this case also, except shortly after a 
meal containing much carbohydrates, the blood of the hepatic vein 
shows an excess of dextrose over that of the portal vein. The 
amount of dextrose thus introduced into the circulation is sub- 
stantially the same as in the first case, and its percentage in the 
blood is not perceptibly altered. The source of this dextrose, how- 
ever, is not so simple a question, since it is possible that all or a 
considerable portion of it may be supplied directly or indirectly 
by the dextrose resorbed by the intestinal capillaries. 
Granting the continual production of sugar by the liver, sub- 
* Die Zuckerbildung im Thierkérper, p. 115. 
