SECRETION. 409 



stored as glycogen. He thus accounts for the production of sugar 

 in the body, even in the absence of all sugar and starch from the food. 

 Pavy believes that the glycogen produced in the liver is utilized in the 

 formation of fat and the synthesis of complex proteids necessary to 

 the construction of the tissues. 



Influence of the Nerve System. The nerve system influ- 

 ences in some way the glycogenic function of the liver. It was 

 discovered by Bernard that puncture of the floor of the fourth ven- 

 tricle at a point between the acoustic and vagus nerves, near the middle 

 line is followed within an hour or two by the appearance of sugar in 

 the urine, which lasted for twenty-four or thirty-six hours. To this 

 area, in close relation to the vasomotor center, he gave the name 

 " diabetic area." The quantity of sugar excreted in the urine will 

 depend on the amount of sugar previously present in the liver. 

 Through some agency the stored-up glycogen is rapidly converted 

 into sugar discharged into the blood and eliminated by the kidneys. 

 There is no positive evidence that the puncture destroys the vaso- 

 motor center, for the blood-vessels of the liver, or that there is any 

 change in the relation of the blood-vessels to the liver-cells. Never- 

 theless powerful stimulation of the sciatic nerve, or the central end of 

 the vagus which impairs or depresses the vasomotor center, will give 

 rise to a similar production and elimination of sugar. The pathway 

 for the passage of these influences beyond the first thoracic ganglion 

 is unknown, but that it is not by way of the splanchnics or the vagi 

 is evident from the fact that division of either of these nerves is not 

 followed by the appearance of sugar in the urine. 



Diabetes. Diabetes is a chronic disease characterized by the 

 appearance of sugar in the urine in variable amounts. This patho- 

 logic condition nas usually been associated with derangements of the 

 glycogenic function of the liver, though doubtless derangements of 

 other organic functions will produce the same condition. At the 

 present time it is believed that the excretion of sugar by the kidneys 

 depends on two causes: (i) An ineffectual abstraction and storage 

 of sugar due to some impairment in the activity of the liver cells; (2) 

 a rapid cleavage of the proteid constituents of the tissues, in conse- 

 quence of some profound alteration in the nutritive process, whereby 

 their glucose radicals are liberated in unusual amounts. The physi- 

 ologic mechanism by which the normal metabolism of the carbohy- 

 drates is regulated is unknown. That it is complex in character is 

 shown by the phenomena which follow not only puncture of the 

 medulla, but also removal of the pancreas and the administration of 

 various poisons. 



Removal of the pancreas from the body of a dog or other ani- 

 mal is at once followed by a rise in the percentage of sugar in the 

 blood and its elimination by the kidneys. In a short time acetone, 



