886 PHYSIOLOGY OF DIGESTION AND SECRETION. 



and plays an important, indeed, an essential part in the metabolism 

 of sugar in the body. Moreover, considerable evidence has been 

 accumulated to show that the tissue concerned in this important 

 function is not the pancreatic tissue proper, but that composing the 

 so-called islands of Langerhans. In man these islands are scattered 

 through the pancreas, forming spherical or oval bodies that may 

 reach a diameter of as much as one millimeter. The cells in these 

 bodies are polygonal; their cytoplasm is pale, finely granular, and 

 small in amount. The nuclei possess a thick chromatin network 

 which stains deeply. Each island possesses a rich capillary net- 

 work that resembles somewhat the glomerulus of the kidney. 

 Histological work seems to show clearly that the islets are per- 

 manent organs which persist as such in the pancreas, and pre- 

 sumably have, therefore, some specific functional importance.* 



According to Ssbolew,t hgation of the pancreatic duct is fol- 

 lowed by a complete atrophy of the pancreatic cells proper, while 

 those of the islands of Langerhans are not affected. Since under 

 these conditions no glycosuria occurs, while removal of the whole 

 organ including the islands is followed by pancreatic diabetes, the 

 obvious conclusion is that the diabetes is due to the loss of the 

 islands. This conclusion is strengthened by reports from the 

 pathological side. A number of observers (Opie, Ssbolew, Herzog, 

 et al.) 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. The gen- 

 eral belief, therefore, is that these cells furnish an internal secre- 

 tion which is essential in some way in the sugar-metabolism of 

 the body. When the secretion is deficient or absent, diabetes 

 develops. 



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 in 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. In support of this explanation it is found 

 that the respiratory quotient of the depancreatized dog is low, as 

 would be expected if the sugar escaped oxidation. Apparently 

 something is lacking in the normal process, but as the nature 

 of the normal process is itself incompletely known, the defect 

 caused by the failure of the pancreatic hormone becomes cor- 

 respondingly diflScult to define. Clark J reports experiments in 



* Bensley, "American Journal of Anatomy," 12, 297, 1912. 

 t "Virchow's Archiv," 168, 91, 1902; also Homans, "The Journal of Med- 

 ical Research," 30, 49, 1914. 



X Clark, "Journal of Exp. Medicine," 1917. 



