METABOLISM 205 



sidered to be a true reflex center, and may be stimulated by 

 afferent impulses. Thus if the vagus is severed and the central 

 end stimulated, sugar appears in the urine. If the splanchnics 

 are cut, there is no glycosuria after puncture. Thus evidently, 

 it is only liver glycogen which is affected by puncture, and the 

 impulses are carried to the liver by the splanchnics. Glycosuria 

 produced by "diabetic puncture" is known as "puncture dia- 

 betes." 



A second factor which apparently is connected with the con- 

 trol of liver glycogen is the secretion of the suprarenals, adrena- 

 line. If adrenaline is injected, an increase of blood sugar 

 occurs, which has its source in liver glycogen, since no glycosuria 

 results if the glycogen supply of the liver has been exhausted. 

 It has been suggested that the action of the sugar center in the 

 medulla is by way of the suprarenals. This problem is still in 

 doubt ; it is probable that the sugar center works by direct stimu- 

 lation of the liver cells, but is aided and supplemented by the 

 adrenaline secreted from the suprarenals. 



Recently Langfelt has published interesting studies on liver 

 diastase, the enzyme which brings about glycogenolysis (break- 

 ing down of glycogen). This enzyme, in the form of its 

 chlorine derivative, acts best at a pH of 6.8, and in the form of 

 its phosphate derivative at a pH of 6.2. In the presence of 

 adrenaline the optimum pH was 7.73. The pH of the blood is 

 about 7.33. Although the pH of the tissues is not known, they 

 are considered to be a little less alkaline than the blood. On this 

 basis, the presence of adrenaline would affect the diastase in 

 such a way that its optimum pH came nearer the pH of the 

 tissues, its activity would be increased and glycogen would be 

 broken down more rapidly into glucose. These findings agree 

 well with the known fact that injection of adrenaline causes 

 an increase of blood sugar. 



The pancreas has been shown to play an important part in the 

 utilization of sugar by the body. This is connected with the 

 burning of the sugar as fuel and also with the storage of gly- 

 cogen in the liver. If the pancreas of an animal is removed, 



