On the Relation of the Islets of Langerhans to the alveoli of the Pancreas. 199 



may be indnced by exhausting the pancreas with secretin . . . Although 

 the islets of Langerhans cannot be regarded as in any sense a tissue 

 sui generis, their abundant capillary supply and the nature of their 

 protoplasm suggest that they may have an internal secretion, though 

 we do not. consider the evidence on this point to be conclusive." 



These views are highly interesting, and based as they are upon 

 the woi'k of experienced investigators demand careful consideration. 

 That the results obtained by these observers involve the general con- 

 clusion that the islets "cannot be regarded as in any sense a tissue 

 sui generis"" appears to me however, premature, and ex parte in the 

 sense that such a conclusion does not allow for certain established 

 facts in the morphology of these structures. 



I propose therefore to deal briefly with some of the difficulties which 

 appear to me to lie in the way of a full acceptance of this conclusion. 



In the first place it is to be noted that the evidence as to the 

 effect of occlusion of the duct is contradictory. Tschassownikow is the 

 latest experimenter in this line, and he finds that the islets are un- 

 doubtedly preserved, although they may be altered in size and form 

 through the growth of connective tissue. Dale found as already quoted 

 that in the course of a few weeks most of the pancreatic tissue dis- 

 appeared, and that "that which escapes destruction assumes a form 

 resembling the islets, but the already existing islets exhibit no special 

 immunity from the destructive efiects of the operation". We may be 

 excused if we express no surprise at this last mentioned result after 

 an operation lasting a few weeks one effect of which is to induce an 

 abundant growth of connective tissue. It may be suggested as recon- 

 ciling the results of these two observers that under the conditions of 

 this experiment degenerative changes of the pancreatic tissue simulating 

 islets do occur, or that the pancreas reverts to "an embryonic condition", 

 and that if the experiment is not too prolonged, the true islets will 

 be found to persist. It is not proved that their disappearance in 

 Dale's experiment is not traceable to secondary causes. In connection 

 with these and analogon experiments there is further the important 

 difficulty of estimating the effect of the experiment, owing to our 

 ignorance of the amount of islet tissue in any individual animal at the 



