STUDIES ON THE PANCREAS OF THE GUINEA PIG 373 



The question we now have to consider is: If a cell of an acinus 

 were being transformed into an islet cell, through what stages 

 would it be expected to go, and conversely if an islet cell were 

 being transformed into an acinus cell what would be the phases 

 of this transformation? I think it is clear, that we must consider 

 all phases of this change before we decide lightly that it is a change 

 "of one element into another, that is, we must show not only the 

 phases of the disappearance of the specific elements at one end 

 of the series, but also the appearance of the specific elements at 

 the other end. The number of stages which could be expected in 

 this process would depend to a large extent on the rapidity with 

 which the change proceeded, but it is reasonable to suppose that 

 this change could not go on with too great a rapidity to permit 

 the discovery of intermediate phases, because the anatomical 

 construction of an islet, which does not contain centroacinous cells 

 and which has a peculiar blood supply, necessitates a consider- 

 able degree of anatomical rearrangement in constructing islets out 

 of acini. 



It seems to me that to be a satisfactory evidence that this 

 change of acinus into islets, or vice versa, is going on, one of the 

 following possibilities would require to be fulfilled: 



1. It should be possible to find intermediate cells which contain 

 at one and the same time islet granules and one of the constit- 

 uents of the acinus cell, that is, zymogen or chromophile sub- 

 stance; or 



2. It should be possible to find a graded series showing, the 

 gradual disappearance of the characteristic constituents of the 

 acinus cells, and, step by step, the appearance of the granules 

 which are characteristic of the islet cells; or 



3. It should be possible to find acini containing well defined 

 centroacinous cells but with islet cells instead of acinus cells. 



Failing transitions which fulfil one of these requirements, we 

 would be obliged to fall back upon less satisfactory evidence of 

 an indirect sort to prove transformation. It is conceivable that 

 the process of transformation is begun by the obliteration of the 

 lumen of the acinus. In this case we should find acini in contin- 

 uity with islets but detached from their ducts. Similarly, if we 



