670 METABOLISM 



enzyme glycogenase, which is present, not only in the liver cell, but 

 also in the blood and lymph. If is a difficult matter to explain why 

 glycogen should be able to exist at all in the liver cells in the presence 

 of this powerful enzyme. The following possibilities may be considered: 

 (1) That glycogenase does not really exist in the living liver cells, but 

 is a postmortem product; (2) that, although present, glycogenase is pre- 

 vented from acting on the glycogen in the living liver cell on account of 

 the latter being protected from its influence by combination with the 

 sustentacular substance; or (3) that some chemical substance in the liver 

 cell prevents the glycogenase from acting on the glycogen an anti- 

 glycogenase. Since the removal of any one of these inhibiting influ- 

 ences would cause glycogenolysis to become excessive, and so bring 

 about hyperglycemia, it is important, in searching for the possible 

 causes of this condition, to examine the evidence that has been brought 

 forward in support of each of these views. 



Against the view that glycogenase is a postmortem product may be 

 cited the very rapid conversion into glucose that occurs when glycogen 

 is added to living blood, as by injecting some into a vein. On account of 

 the active glycogenolytic action of blood, it has been suggested that 

 during life glycogen does not become transformed into glucose until 

 after it has been discharged into the blood from the liver cell. When 

 increased sugar must be mobilized, glycogen passes unchanged, or per- 

 haps as seme dextrine, into the blood and lymph of the liver capillaries 

 and lymphatics, the glycogenase of which converts it into glucose, the 

 conversion being so rapid that, by the time the blood has traveled from 

 the liver through the heart and pulmonary vessels to the arteries, all 

 the glycogen has already become transformed into glucose. Postmortem 

 glycogenolysis, according to this view, is due to the opposite occur- 

 rence the transference of glycogenase from the blood into the liver 

 cell. Some facts supporting this view are as follows: (1) It has been 

 found that the amount of free glucose in the blood of the vena cava 

 is sometimes less than in that collected simultaneously from the carotid 

 artery. (2) After giving certain substances, such as phosphorus or 

 peptone, there is distinct diminution in the amount of glycogen in the 

 liver, accompanied, however, by no increase in the amount of glucose 

 in the blood. And (3) if the liver of an animal that has been rendered 

 diabetic by stimulation of the splanchnic nerve or by puncture of the 

 floor of the fourth ventricle is examined microscopically, after staining 

 by the carmine method, masses of stained glycogen can be found present 

 in the capillaries (sinusoids) that lie among the liver cells. 



According to the second view, the glycogen is removed from the 

 influence of the intrahepatic glycogenase on account of its combination 



