METABOLISM 185 



ternal secretion. The evidence for this is not conclusive, how- 

 ever, and it is still uncertain where in the gland the substance 

 is formed. 



Still another factor is concerned in the control of glucose 

 utilization in the body, and that is the influence of the kid- 

 neys. It has been stated that the kidneys are "set" to retain a 

 definite percentage of sugar in the blood. The kidneys may be 

 injured by the injection of the drug phloridzin. There is no 

 increase in the level of blood sugar, but sugar appears in the 

 urine for several hours. The amount of sugar in the blood falls 

 below the normal. The mechanism of the process is undecided. 

 Possibly the excretion of glucose is an active process, and not 

 simply the passive action of a dam to keep back a certain amount 

 of sugar. In this case phloridzin might act by stimulating the 

 excretion of sugar by the kidneys. It is of interest in this con- 

 nection that the drug causes marked degeneration of kidney 

 epithelium. There is some reason to believe that phloridzin 

 causes excretion of glucose in organs other than the kidneys. 



Much speculation has been expended on the cause of diabetes 

 in man and its possible relationships to one or other of the forms 

 of experimental diabetes discussed, i.e., puncture diabetes, pan- 

 creatic diabetes or phloridzin diabetes. Obviously it is not 

 analogous to the last form, for the disease is accompanied by 

 increased sugar content of the blood. Clinicians generally are of 

 the opinion that it is closely allied to pancreatic diabetes. Evi- 

 dence, however, is not absolutely conclusive as yet, though it is 

 generally believed that lesions in the pancreas are usually if not 

 always the cause of the disorder. 



A review of the foregoing discussion will emphasize the fact 

 that the internal factors regulating carbohydrate metabolism in 

 the body include a center in the medulla, presiding over the 

 conversion of liver glycogen into blood sugar, the internal secre- 

 tion of the suprarenals, operative in a similar way, the internal 

 secretion of the pancreas, without which sugar cannot be burned 

 by the cells, and the nature of the kidney, which regulates the 

 level of sugar in the blood. 



