638 INTERNAL SECRETION ENDOCRINE GLANDS 



(p- 554). has been asserted by some observers and denied by others. 

 A great production of sugar from proteins (i.e., from amino-acids) 

 has been demonstrated, but it is quite possible that just as much is 

 produced from this source in the normal organism, although here 

 its formation is masked by a corresponding utilization. 



The clearest evidence that the pancreas produces something of 

 high importance in carbo-hydrate metabolism has been obtained 

 by experiments in which animals were united in such a way 

 that substances could pass from one to the other (parabiosis, see 

 Chap. XIX.). When two young dogs were so united and the pancreas 

 then removed from one, no glycosuria followed. The internal 

 secretion of the remaining pancreas was sufficient for both (Forsch- 

 bach). In like manner the removal of the pancreas from pregnant 

 bitches not far from full term caused no glycosuria or very little 

 till the pups were born, when the usual train of events associated 

 with pancreatic diabetes ensued. Obviously the pancreatic tissue 

 of the embryos in the uterus supplied the mother with the indis- 

 pensable secretion (Carlson and Drennan). 



The question has often been raised why it should not be possible 

 to supply animals or human beings suffering from pancreatic defi- 

 ciency with the missing material by administering pancreas or 

 pancreatic extracts. Hitherto, however, little if any success has 

 attended attempts of this kind, perhaps because the active substance 

 or substances are very easily destroyed. This has been all the more 

 disappointing, as in the case of the internal secretion of the thyroid 

 the so-called ' substitution therapy ' has been brilliantly successful 

 (p. 649). 



The seat of the internal secretion of the pancreas seems to be the 

 very vascular epithelioid tissue which is peculiar to this gland, and 

 occurs in islands between or imbedded in the alveoli (islands or 

 islets of Langerhans) (Schafer). For animals survive the complete 

 atrophy of the ordinary secreting epithelium caused by the injec- 

 tion of paraffin into the ducts, and no sugar appears in the urine. 

 The islets remain intact. When a portion of the pancreas is 

 separated from the rest, and its duct ligated, it undergoes extensive 

 atrophy, a tissue remaining which is apparently composed of en- 

 larged islands of Langerhans and remains of pancreatic ducts. If 

 the rest of the gland is now removed, no glycosuria occurs, even 

 when considerable quantities of dextrose are injected. But when 

 the atrophied remnant is also removed, typical pancreatic glycosuria 

 at once ensues (W. G. MacCallum). 



As further evidence that the islets have a different function from 

 the pancreatic alveoli may be cited the statement that in teleostean 

 fishes, in which the islands are so large that they can be separated 

 from the rest of the tissue, the cells of the islets, instead of containing 

 an amylolytic ferment like the alveolar cells, contain a glycolytic 



