432 ANIMAL PHYSIOLOGY. 
any theories that, like a scaffolding, allow of or help to addi- 
tional investigation, and in any way lead out into a clearer 
light, are not without value; and on this principle we shall 
treat the subject, spending but little time in barren fields 
except as they have an interest from the suggestiveness of the 
results, even though negative. 
THe METABOLISM OF THE LIVER. 
This organ has two well-recognized functions: 1. The for- 
mation of bile. 2. The formation of glycogen, 
We have already considered the first,and ascertained how 
little.is positively known. Let us now examine the second. 
Glycogen may be obtained from the liver of mammals, such 
as the rabbit, by rapidly killing the animal, excising the warm 
still living organ, cutting into fine pieces, throwing them into 
boiling water, removing after a few minutes and grinding ina 
mortar and reimmersing in the boiling water; on now passing 
the latter through a coarse filter a turbid, whitish fluid is ob- 
tained containing the extracted glycogen as proved by giving 
a red color with solution of iodine. The substance may be ob- 
tained as a whitish amorphous powder, having the chemical com- 
position of starch, and has in fact been termed animal starch. 
By appropriate treatment it may be converted into sugar by 
a process of hydration (C,H,O; + H.O = C.H,.0,). 
If, after the death of an animal, the liver be kept at body 
temperature for, say,an hour, very little glycogen can be recov- 
ered from it, but instead abundance of sugar. These facts sug- 
gest that the sugar present represents the original glycogen, 
and that the conversion has been effected by some ferment, 
which does not act during life, though why not is one of the 
problems ranking with the non-digestion of the stomach by its 
own ferments, etc. 
We have already expressed our doubts as to the justifia- 
bility of resorting to so many “ ferments” to explain the facts 
of physiology, and in the present case there is another possible 
view of the matter. It is conceivable that the conversion, 
under these circumstances, of the glycogen into sugar, may be 
an act of the dying protoplasm of the liver-cells; and there are 
experimental results which tend to strengthen such a view. 
The principal facts as to the storage of glycogen in the liver 
may be briefly stated thus: 
1. Glycogen has been found in the liver of a large number 
