376 R. R. BENSLEY 



show the characteristic granules of islet cell by vital staining with 

 neutral red, or in preparations by methods which have been found 

 to be adequate. Earlier in this paper, I have answered this 

 question by showing that the assumption of Dale that secretin 

 increases the number of islets is unwarranted by the facts. The 

 examination of fixed material from guinea pigs and toads which 

 have been long stimulated by secretin confirms this opinion for 

 in the sections of this material I find the cells described by Dale, 

 but when stained by methods which bring out the islet granules 

 they are found to contain none. They are, therefore, not islet 

 cells at all but simply exhausted acinus cells. 



Dale and Vincent and Thompson give figures which are de- 

 signed to show transformation of acinus tissue into islet tissue, 

 by showing acini on the edge of islets which are apparently merely 

 half acini, or acini in the midst of islet tissue. These appearances 

 become clear when one sees the islets of the dog, toad, etc., in 

 toto, in preparations stained intra vitam with janus green. In 

 these preparations, it may be seen that the peculiarities of shape 

 of the islets are sufficient to account for any relation of islet tis- 

 sue to acinus tissue in sections. Islets even occur which are ring- 

 shape, a section through the middle of which would show islet 

 tissue completely surrounding acini, though a series of sections 

 would quickly demonstrate the fact that these acini are in reality 

 continuous with other acini. 



Tschassonikow ('06) described the A cells in the islet as transi- 

 tions, between the acinus cells and the B cells. On what grounds 

 he came to this conclusion I do not know, because his main pub- 

 lication on this topic is unfortunately unavailable to me. This 

 conclusion I have already discussed in connection with the re- 

 marks concerning the relation of the several types of islet cells 

 to one another, and have shown that it is untenable. If we accept 

 the A cells as transitions, then, we are entitled to ask where may 

 be the transitions between acinus cells and A cells for the latter 

 are as different from the acinus cells as are the B cells, since they 

 contain neither zymogen granules nor basophile substance, and 

 since their mitochondria are different from those of the acinus 

 cell. I fear that the idea, that A cells are transitions, is merely 



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