806 PHYSIOLOGY OF DIGESTION AND SECRETION. 



This conclusion is strengthened by reports from the pathological 

 side. A number of recent observers (Opie, Ssbolew, Herzog, et a/.) 

 find that in diabetes mellitus in man the islands may be markedly 

 affected. They show signs of hyaline degeneration or atrophy or in 

 severe cases may be absent altogether. It should be added that 

 this connection of the islands of Langerhans with the internal 

 secretion of the pancreas is by no means a demonstrated fact. 

 Several observers * contend that the islands represent a stage in the 

 development of the ordinary secreting alveoli of the pancreas. 

 When the pancreas is subjected to prolonged and excessive activity, 

 by the injection of secretin, for example, the number of islands is 

 greatly increased, and the same result follows periods of prolonged 

 inactivity, as in fasting. 



Several theories have been advanced to explain the action of 

 the internal secretion of the pancreas. It has been suggested that 

 the secretion contains an enzyme which is necessary for the hydrol- 

 ysis or oxidation of the sugar of the body and in the absence of 

 this enzyme the sugar accumulates in the blood and is drained off 

 through the kidney. Cohnheimf states that, while the juices ex- 

 pressed from muscle and from pancreas have little effect upon sugar 

 when taken separately, yet when combined they cause a marked 

 disappearance (glycolysis) of sugar added to the mixture. The 

 inference from this result is that the pancreas furnishes a substance 

 which activates the glycolytic enzyme or enzymes of the muscle 

 and thus makes possible the physiological consumption of sugars 

 in the body. Since the pancreas extracts do not lose this property, 

 upon boiling it is evident that the activating substance is not an 

 enzyme, but a body of a more stable character. Other investigators 

 adopt an entirely different view of the relation of the pancreas to 

 carbohydrate metabolism. They believe that the internal secre- 

 tion of the pancreas regulates in some way the output of sugar 

 from the liver (and other sugar-producing organs). In the absence 

 of this secretion the liver gives off its glycogen as sugar too rapidly, 

 the sugar contents of the blood are thereby increased (hypergly- 

 cemia) above normal, and the excess passes out in the urine. 



Kidney. Tigerstedt and Bergman t state that a substance 

 may be extracted from the kidneys of rabbits which when injected 

 into the body of a living animal causes a rise of blood-pressure. 

 They get the same effect from the blood of the renal vein. They 

 conclude, therefore, that a substance, for which they suggest the 



* Dale, "Philosophical Transactions," B. cxcyii., 1904 ; also Vincent and 

 Thompson, "Journal of Physiology," 1906, xxvii., xxxiv. 



fCohnheim, "Zeitschrift f. physiolog. Chemie," 39, 336, 1903; also 1904. 



J " Skandinavisches Archiv f. Physiologic," 8, 223, 1898; see also Brad- 

 ford, 'Proceedings of the Royal Society," 1892. 



