STUDIES ON THE PANCREAS OF THE GUINEA PIG 375 



In discussing the effect of prolonged secretin stimulation Dale 

 adds: 



It can be seen that, apart from the large masses of definite islet tissue 

 such as the low power shows, a large proportion of the remaining alveoli 

 show partial change into what must now be called the islet condition, 

 some of the cells having lost their normal staining properties and having 

 become assimilated to the centroacinary cells. 



Similarly Vincent and Thompson ('07) in describing the islets 

 of the guinea pig say: "Transitions are so common that, in the 

 majority of the islets, it is quite impossible to define their limits 

 under a high power, since the two tissues fade gradually into each 

 other. There is a comparatively wide zone of cells which partake 

 in a varying degrees of the characters of zymogenous and islet 

 cell." Describing the islets of the dog the same authors say: 

 "There are all transitions to be found between the most strongly 

 granulated of alveolar cells and the clearest of islet cells." 



It is quite apparent that the three authors in question have 

 considered in this connection only the loss of the basophile sub- 

 stance and of zymogen granules, and that they were quite willing 

 to identify as an islet cell any cell not in a duct which had neither 

 zymogen nor basophile substance. There is no indication what- 

 ever that they have given any consideration to the specific gran- 

 ules of the islet cells, which Dale says he was unable to find, and 

 which Vincent and Thompson mention, but ignore when discuss- 

 ing transitions. Their work is based on the incorrect assumption 

 that islet cells do not differ from duct cells and their whole case 

 falls to the ground when it is shown that the assumption is un- 

 sound. 



If Vincent and Thompson had employed the methods of Tschas- 

 sonikow ('06) for the study of the islets of the guinea pig, their 

 difficulties in defining the actual limits of the islets under the 

 microscope would have vanished, for as a matter of fact the tran- 

 sition zone which they describe does not exist, as may be seen from 

 my figures of the neutral red preparations. 



The question, however, still remains whether the cells described 

 by Dale as produced from acinus cells by long stimulation with 

 secretin are islet cells or not. If they are islet cells they should 



