434 ANIMAL PHYSIOLOGY. 
The Uses of Glycogen.— Whether the blood of the hepatic vein 
contains more sugar than that of the portal vein has long been 
a subject of controversy. Ifthe affirmative could be established, 
it would be pretty clear that glycogen stored in the liver-cells 
was transformed into sugar, possibly by a process of hydration, 
But, considering the rapidity of the blood-stream, it is easy to 
understand that a large amount of sugar might be conveyed 
cz Main venous trunk 
Right auricle 
Vena cava: 
Lymph. gland 
Hepatic vein: 
Lymphatic 
Portal system Og , Blood vessel, tissue cells, 
h-spaces 
wi lymp 
Fic. 329.—Diagram intended to illustrate the general relations of blood and lymph to metab- 
olism (nutrition); and the method by which the portal, lymphatic, and general venous 
systems are related to the alimentary tract. 
Alimentary tract 
into the general circulation, and yet the blood, whether of the 
hepatic vein or of other parts, contain but a small quantity at 
any one time. The blood is kept of a certain fairly constant 
composition, both by the action of the excreting organs and by 
the withdrawal from it of supplies for the tissues. Moreover, 
that correlation of functional work on which we have already 
insisted, is not to be forgotten. One must not conceive of the 
liver-cells or any others doing their work independently of the 
condition of their fellow cell-units in the organic common- 
wealth. We mean to say that the amount of glycogen trans- 
formed to sugar will depend on a great many circumstances 
outside of the liver itself. Such aspects of the case have been 
rather overlooked. According to another theory, glycogen is 
an intermediate product between sugar and fat, but of this 
there is very little evidence indeed; and, besides, fat formation 
is otherwise well enough accounted for, though, of course, too 
much stress must not be laid upon such an argument. 
What is the fate of the transformed glycogen ? What be- 
comes of the sugar? We can answer, negatively, that it is not 
