374 R. R. BENSLEY 



can show that there is a quantitative variation of the reciprocal 

 amounts of islet and acinus under difTerent experimental condi- 

 tions, we have in that fact satisfactory evidence that one tissue 

 is increasing at the expense of the other. 



We may now proceed to discuss the transitions which have been 

 described by various authors as indicating a transformation of 

 one tissue into the other. 



The transitions described by Dale ('05), and those described 

 by Vincent and Thompson ('07) are of the same sort and may be 

 considered together. The conception which Dale had of the struc- 

 ture of an islet cell is well indicated in the statement that " occa- 

 sionally, but rarely in the resting gland, an islet may be found, 

 which is apparently continuous with the epithelium of a ductule, 

 and the similarity of the islet cells to those of the epithelium is 

 then very obvious." This, it need hardly be mentioned, is a 

 negative similarity and does not necessarily mean any more than 

 would a similar comparison of the islet cells and the epithelium 

 of the bile duct. Again, he says: 



With a high power many of the islets show a division of the cells, by 

 intervening connective tissue and blood capillaries into packets which 

 have a shape strikingly similar to that of the secretory alveoli. In 

 such, an outer layer of large cells can be distinguished from an inner 

 layer of smaller cells exactly like centroacinary cells. The appearance 

 in fact is exactly that of a group of alveoli in which the secreting cells 

 have lost their characteristic basal basophile staining and zymogen 

 granules, their nuclei having become more centrally placed, and assim- 

 ilated to those of the centroacinary cells, and in which the lumen has 

 been obliterated by a falling together of the cells. 



The deceptive alveolar arrangement here is due to a section 

 across a cell column of the islet with A cells surrounding B cells. 

 In another place he sums up the evidence in favor of the theory 

 of transformation as follows: 



The unequal distribution of the staining reaction, so that an isolated 

 cell or part of a cell shows the basophile reaction, which fades away to- 

 wards its edge; the presence of cells which have no })asophile reaction, 

 but retain a few eosinophile granules, which appear to be undergoing 

 solution; the faint trace of an alveolar outline, like the shadow of a struc- 

 ture which is being lost. . . . 



