CH. XXXV.] DIABETES 539 



that injury to the floor of the fourth ventricle in the region of the vaso- 

 motor centre leads to glycosuria. In man, also, disease of the bulb is 

 frequently associated with glycosuria. These observations led to the 

 erroneous conclusion that diabetes is always of nervous origin. The 

 diabetes produced in this way cannot be the result of vaso-motor 

 disturbances, but is due to an influence on the glycogenolytic nervous 

 mechanism (see p. 541), and the glycosuria only occurs when the 

 liver has within it a store of glycogen. 



(2) By extirpation of the pancreas. Minkowski and v. Mering 

 in 1889 showed, that complete extirpation of the pancreas produces 

 in animals a diabetic condition, even if no carbohydrate food is 

 contained in the diet. The disease terminates fatally within a few 

 weeks. If the removal is not complete, the intensity of the glyco- 

 suria depends upon the amount of pancreatic tissue left behind. 

 One-fourth to a fifth of the gland is usually sufficient to prevent the 

 occurrence of the diabetic state. It does not depend on the connec- 

 tion of the pancreas with the intestine, and this proves that the 

 suppression of pancreatic juice is not the cause of the diabetes. The 

 same conclusion was reached in other experiments in which the 

 gland ducts were occluded by paraffin wax ; no glycosuria resulted. 

 Moreover, the effect of pancreatic extirpation, so far as diabetes is 

 concerned, can be prevented by grafting a portion of the pancreas 

 into the abdominal wall, or even under the skin. It is therefore 

 believed that the pancreas forms an internal secretion, in addition to 

 its external secretion or pancreatic juice. The former passes into 

 the blood and plays an essential part in carbohydrate metabolism. 



The islets of Langerhans have by many been held responsible for 

 this portion of the duties of the pancreas. The evidence in favour of 

 this view is that in human diabetes the islets are frequently 

 degenerated, atrophied, or even absent ; in animals, ligature of the 

 pancreatic ducts leads to atrophy of the pancreatic acini, but not of 

 the islets, and under those conditions no glycosuria occurs. 



This view may be accepted with considerable confidence, for the 

 observations of certain investigators that the islets merely represent 

 a stage in the development of the ordinary acini, have been 

 disproved or at any rate discredited. 



We have seen that in diabetes, the power of the tissue cells to 

 burn sugar is lessened; nevertheless, other diseases in which 

 diminished oxidation occurs are not necessarily accompanied with 

 glycosuria. The difficulty in diabetes probably lies in an impair- 

 ment of the capacity of the cells of the body to prepare the sugar 

 for oxidation. In this process the sugar or its derivative glycuronic 

 acid is split into smaller molecules, and ultimately into water and 

 carbon dioxide. If two hydrogen atoms in the CH 2 OH group of 

 dextrose are replaced_by one of oxygen, we obtain glycuronic acid. 



