METABOLISM. 23 
cident with this disappearance of dextrose, there is an increase in 
the carbon dioxide of the blood and a decrease of its oxygen. 
The relations of the dextrose of the blood to the evolution of 
heat and work in the muscles and other tissues, so far as they are at 
present understood, will be considered in a subsequent chapter. 
For our present purpose it suffices to note the fact that it disappears 
in the capillaries with the ultimate production of carbon dioxide 
and water. That the dextrose is immediately oxidized to carbon 
dioxide and water, however, is extremely unlikely. It has been 
suggested that the lactic acid which is found in the muscle after 
muscular contraction is one of the intermediate products of the 
oxidation. Several considerations, however, seem to render it 
more probable that the dextrose first enters in some way into the 
constitution of the muscles, or in other words, that a synthetic or 
anabolic process precedes the katabolic one. 
Muscutar Guiycocen.—Another fact, of much interest in this 
connection, is that the muscles (and other tissues also), as well as 
the liver, contain glycogen. Moreover, the muscular glycogen 
diminishes or disappears during work and reappears again after 
rest. It would appear, then, that the muscular tissue shares with 
the liver the ability to form glycogen. As in the case of the former 
organ, the simplest supposition is that this glycogen is produced 
from the dextrose supplied in the blood, and Kitz * and others 
have shown that subcutaneous injections of sugar give rise to a 
formation of muscular glycogen in frogs whose livers have been 
removed. On the other hand, of course, the considerations pre- 
sented above relative to the sources of the liver glycogen apply, 
ceteris paribus, to the formation of glycogen in the muscles. Neither 
the source nor the exact functions of the muscular glycogen are 
yet beyond controversy, but the facts just stated strongly suggest 
a storing up of reserve carbohydrates during rest to be drawn upon 
when there is a sudden demand for rapid metabolism. 
Far Propuction.—In addition to its important relation to the 
muscles, the dextrose of the blood likewise supplies nourishment 
for the fat tissues of the body. Hitherto we have spoken as if the 
supply of dextrose to the blood were determined substantially by 
* Neumeister, Physiologische Chemie, p. 322. 
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