Si8 A MANUAL OF PHYSIOLOGY 



activated by another substance, as trypsinogen is activated by 

 enterokinase (p. 343). This announcement aroused great in- 

 terest, since it is known that the pancreas is intimately concerned 

 in the metabolism of sugar. Unfortunately, however, the accu- 

 racy of Cohnheim's observation is still disputed. Excision of 

 the pancreas in dogs causes permanent glycosuria (pancreatic 

 diabetes) (v. Mering and Minkowski), which is prevented if a 

 portion of the pancreas be left (p. 553). Diabetes in man is 

 known to be frequently associated with pancreatic lesions. 



Diabetes. In the disease known as diabetes mellitus, sugar 

 accumulates in the blood, and is discharged by the kidneys, 

 and it has been supposed that a derangement in the glycogenic 

 function of the liver is sometimes the cause of this accumulation 

 and of this discharge. An artificial and temporary glycosuria, 

 in which the sugar in the urine undoubtedly arises from the 

 hepatic glycogen, can, indeed, be caused by puncturing the 

 medulla oblongata in a rabbit at or near the region of the vaso- 

 motor centre. If the animal has been previously fed with a diet 

 rich in carbo-hydrates that is, if it has been put under con- 

 ditions in which the liver contains much glycogen the quantity 

 of sugar excreted by the kidneys will be large. If, on the other 

 hand, the animal has been starved before the operation, so that 

 the liver is free, or almost free, from glycogen, the puncture will 

 cause little or no sugar to appear in the urine. That nervous 

 influences are in some way involved is shown by the absence 

 of glycosuria if the splanchnic nerves, or the spinal cord above 

 the third or fourth dorsal vertebra, be cut before the puncture 

 is made. But sometimes these operations are themselves 

 followed by temporary glycosuria. Section of the vagi has no 

 effect either in causing glycosuria of itself or in preventing the 

 ' puncture ' glycosuria, although stimulation of the central 

 ends of these and of other afferent nerves may cause sugar to 

 appear in the urine, but not if precautions are taken to prevent 

 any degree of asphyxia. Asphyxia produces an increase in the 

 sugar content of the blood (hypergly caemia) , an increase in the 

 flow of urine and glycosuria. Under normal conditions the rate 

 of transformation of the hepatic glycogen into dextrose is ad- 

 justed in some way to the dextrose content of the blood, so that 

 when the latter tends to sink more dextrose is produced in the 

 liver ; when it tends to rise more glycogen is laid up in the 

 hepatic cells. Thus, the great function of the glycogen store of 

 the liver is to regulate the proportion of sugar in the blood. 

 Although several of the operations which lead to temporary 

 glycosuria undoubtedly bring about changes in the hepatic 

 circulation, it is as yet impossible to say whether the whole 

 phenomenon is at bottom a vaso-motor effect, or is due to direct 



