706 METABOLISM 



tacking the glycogen. In the former case the glycogen liberated from its union with 

 the sustentacular substances would either become attacked by the glycogenase present 

 in the liver cell itself or it would first of all migrate, as glycogen, into the blood capil- 

 laries and there be attacked by the blood glycogenase. Evidence for the possibility of 

 the occurrence of such a process lias already been given (page 702). The chemical 

 'change referred to under the second possibility might consist in an alteration in the 

 hydrogen-ion concentration of the liver cell, a change, however, which for obvious reasons 

 it is impossible to investigate. 



Nervous Diabetes in Man, The main interest attaching to the inves- 

 tigation of these nervous forms of experimental diabetes depends on the 

 insight which they afford us into the nature of the mechanism by which 

 a prompt mobilization of glucose may be brought about in the normal 

 animal. There is also some evidence that a relationship may exist be- 

 tween certain of the clinical varieties of the disease in man and repeated 

 excitation of glycogenolysis brought about by nerve stimulation. In- 

 creased glucose output from the liver as a result of nerve excitation 

 may be a normal process, but there is reason to believe that frequent 

 repetition of this process tends to induce a permanent rise in the glucose 

 level of the blood and therefore a tendency to diabetes. There have 

 recently been collected several facts which lend some support to this 

 view. The frequent occurrence of diabetes in those predisposed by 

 inheritance to neurotic conditions, or in those whose daily habits entail 

 much nerve strain, and the aggravation of the symptoms which is likely 

 to follow when a diabetic patient experiences some nervous shock, all 

 point in this direction. 



Diabetes is common in locomotive engineers and in the captains of 

 ocean liners that is, in men who in the performance of their daily duties 

 are frequently put under a severe nerve strain. It is apparently in- 

 creasing in men engaged in occupations that demand mental concentra- 

 tion and strain, such as in professional and business work. Cannon 23 

 found glycosuria in four out of nine students after a severe examination, 

 but only in one of them after an easier examination.* In the urines of 

 twenty-four members of a famous football squad, f sugar was found pres- 

 ent in twelve immediately after a keenly contested game. Anxiety and 

 excitement must have been responsible for its appearance, since five of 

 the twelve players were substitutes who did not get into the game. 



Although these nervous conditions, by excitement of hepatic glyco- 

 genolysis, produce at first nothing more than an excessive discharge of 

 sugar into the blood a condition which is exactly duplicated in our 

 laboratory experiments by stimulation of the nerve supply of the liver 

 their repetition may gradually lead to the development of a permanent 

 form of hyperglycemia. To prevent the repetition of these transient 



*We have been unable to confirm this observation even though the examinations were made 

 unusually "nerve-racking." 



