STUDIES ON THE PANCREAS OF THE GUINEA PIG 299 



differences of opinion. It is difficult to understand, for example, 

 why one group of investigators maintain that the islets of Langer- 

 hans are anatomically independent of the rest of the pancreatic 

 tissue, and possess a limiting capsule, while another group 

 maintains just as strongly that they are everywhere continuous 

 with acini or ducts. 



In the opinion of the writer the reasons for these and other 

 differences of opinion are to be found in part in the lack of ade- 

 quate technical methods for the investigation of the pancreas, 

 in part, also, in the inadequate definition of the islet cell which is 

 current in the literature. For, although we know, as a result 

 of the observations of Laguesse ('99), Tschassonikow ('00), 

 Mankowski ('01), Lane ('07), and others, not only that the cells 

 of the islet contain granules which are characteristic of them, and 

 which differ in size, refractive power, and solubility from the 

 granules of the zymogenic cell, but also that there are two types 

 of islet cell which differ inter se in the nature of their granular 

 contents, yet the prevailing definition of an islet cell is by means 

 of negative characters. Thus an islet cell is defined, not by what 

 it has, but by what it has not. It is not difficult to see how far 

 astray such a deffiiition of an islet cell might lead one, for any 

 cell which was reduced by experiment to a sufficient degree of 

 negativity would become ipso facto an islet cell, and thus a wholly 

 false idea of the relations of islet cells to other cells, and of the 

 formation of islet cells would grow up. It was apparently such 

 a definition of islet cells by negative characters that Dale ('05) 

 had in his mind when he described the changes brought about in 

 the pancreas by secretin stimulation as of such a nature as to 

 assimilate all of the cells to those forming the ducts and the centro- 

 acinous cells, and interpreted the cells so modified as islet cells. 

 Similarly Vincent and Thompson ('07) described the conditions 

 found as follows: ''There were all transitions to be found 

 between the most strongly granulated of alveolar cells and the 

 clearest of islet cells;" and again: ''Transitions as indicated by 

 varying amounts of zymogenous granules in the different cells are 

 frequent." It is not difficult to understand why an investigator 

 who regards the islet cell as something having a definite structure 

 and granules peculiar to itself should differ, both as to his account 



