THE METABOLISM OF THE BODY. 477 
pletely, we may sum up the chief results of our present knowl- 
edge (and ignorance) as follows: 
Glycogen is found in the livers of all vertebrate and some 
invertebrate animals. The quantity varies with the diet, being 
greatest with an excess of carbohydrates. 
It seems likely that glycogen is manufactured from the pro- 
toplasm of the liver-cells, though it is possible that the latter 
may act on substances contained in the lymph, and convert 
them into glycogen which they store up. The phenomena of 
diabetes mellitus seem to indicate that vaso-motor effects in the 
liver are not essential to the formation of the excess of sugar 
in that disease, which excess is only one symptom, there being 
frequently also a largely increased secretion of urea; but inas- 
much as the nervous system is greatly deranged in this malady, 
the symptoms, etc., of the disease as a whole may be rather 
regarded as showing how important is the due influence of 
the nervous system. 
Glycogen may be regarded as stored material to be convert- 
ed into sugar, as required by the organism; though the exact 
use of the sugar and the method of its disposal are unknown. 
Fat is not stored up in the body as the result of being 
merely picked out from the blood ready made; butisa genuine 
product of the metabolism of the tissues, and may be formed 
from fatty, carbohydrate, or proteid food. This becomes es- 
pecially clear when the difference in the fat of animals from 
that on which they feed is considered, as well as the direct re- 
a of feeding experiments, and the nature of the secretion of 
milk, 
The liver seems be engaged in a very varied round of.meta- 
bolic processes: the manufacture of bile, of glycogen, of urea, 
and probably of many other substances, some known and 
others unknown, as chemical individuals. Urea is in great 
part probably only appropriated by the kidney-cells (Amceba- 
like) from the blood in which it is found ready-made; though 
it may be that a part is formed in these cells, either from 
bodies some steps on the way toward urea, or out of their pro- 
topiasm, as fat seems to be by the cells of the mammary gland. 
The leucin (and tyrosin ?) of the digestive canal sustains 
some relation to the manufacture of urea by the liver, and 
possibly by the spleen and other organs; for an animal diet 
increases these products, and also the urea excreted. Creatin, 
one of the products of proteid metabolism, and possibly allied 
bodies, may be considered as in a certain sense antecedents of 
