324 R. R. BENSLEY 



may be transformed one into the other in either direction so as to 

 maintain a balance between the functional demands and the rela- 

 tive amounts of the tissue serving them. On the other hand the 

 claims of Dale and Vincent and Thompson that islets are formed 

 from acinus tissue in a brief period of time as a result of secretin 

 stimulation or of inanition, admit of no such functional inter- 

 pretation, nor indeed of any, but that the islet tissue is simply 

 a negative phase of the acinus tissue, notwithstanding the fact 

 that the authors in question express themselves with some reserve 

 on this topic. The confirmation of the results of Dale, Vincent 

 and Thompson would support Laguesse's contentions only to the 

 extent that it would show that acinus cells and islet cells are recip- 

 rocally potent, the disproving of these results on the other hand 

 would affect Laguesse's hypothesis neither one way nor the other, 

 for it would be simply a negative answer to the question of re- 

 spective potencies of the two epithelia and would still leave the 

 field open to a positive result by different experimental methods. 

 It is conceivable that under usual conditions of life a fair degree 

 of permanency of islet tissue may be maintained, while under 

 other conditions a sudden functional demand for a greater rela- 

 tive amount of one or the other tissue may result in the trans- 

 formation of one type of cell into the other. The task of the 

 experimenter is to discover the conditions which will call forth such 

 a response, and as long as his results are negative he is not justified 

 in drawing any conclusion, except such as refers to the direct result 

 of the particular experiment. Thus, complete specificity of 

 islet and acinus inter se can not be proven experimentally, while 

 at least two roads are open for the experimental proof of equi- 

 potency. The first method is to establish a graded series of tran- 

 sition types of cells connecting the acinus cell at one end with the 

 islet cell at the other. This would, however, give us no clue as 

 to the direction of the change. It would show that one type of 

 cell could be changed into the other type without proving that the 

 direction of the change was in one direction to the exclusion of the 

 other, or that the change in both directions was possible. The 

 second method is to show that it is possible to cause a consider- 

 able increase in one or the other tissue in a short period of time 



