METABOLISM 43 



glycogen into sugar. Which of these will prove to be 

 the correct explanation time will doubtless show. 



Puncture Glycosuria. Since the time of Claude 

 Bernard it has been known that puncture of a point 

 in the floor of the fourth ventricle results in the appear- 

 ance of sugar in the urine. The glycosuria so produced 

 disappears when the liver has been emptied of glycogen, 

 and is apparently the result of a disturbance of the blood- 

 supply of the liver through its vasomotor nerves. A 

 similar result is sometimes observed in man in con- 

 sequence of injury to the central nervous system, but the 

 glycosuria which results is transient, and in that way 

 differs from true diabetes. 



Phloridzin Diabetes. In addition to its production 

 by removal of the pancreas and by puncture of the floor 

 of the fourth ventricle, glycosuria may also be produced 

 in animals by the administration of phloridzin, a gluco- 

 side derived from the thorn-apple. The glycosuria so 

 brought about resembles very closely that of true 

 diabetes, and is accompanied also by an acid intoxica- 

 tion identical with that found in the later stages of the 

 disease in the human subject. It has generally been 

 supposed, however, that phloridzin diabetes is brought 

 about by an action of the drug on the ' renal filter,' 

 which it renders more permeable to sugar, and that it 

 has therefore nothing in common with true diabetes. 

 Opposed to this explanation is the fact that much more 

 sugar may be excreted in the urine after the administra- 

 tion of phloridzin than the amount present in the blood 

 will account for, and it would seem that the drug must 



