300 R. R." BENSLEY 



of the facts, and as to their interpretation, from one who thinks 

 that they are simply cells which contain no zymogen granules 

 and no basophile substance. 



It is obvious that before we proceed to study the formation of 

 islet cells from other elements we must know what islet cells are, 

 so as to avoid the error of mistaking for islet cells elements which 

 in reality belong to another category. 



These remarks apply with equal force to observations on the 

 effect of certain experimental conditions on the number of islets 

 of Langerhans in the pancreas. For before we can know what this 

 effect is we must be able to diagnose with certainty islet tissue 

 and not confuse it with other tissues. In this connection, also, 

 it may be pointed out that we do not know for a single species, 

 nor have we an adequate method for ascertaining, the total num- 

 ber of islets of Langerhans in the pancreas, or the normal range 

 of variation in this respect. Yet we have numerous records of 

 experimental researches which deal w4th increase or diminution 

 of the number. For example. Dale and Vincent and Thompson 

 claimed that the number of islets of Langerhans were greatly 

 increased by secretin stimulation and by inanition, while Lewas- 

 chew ('86) claimed a similar increase as the result of pilocarpine 

 stimulation. The careful counts of the islets in sections made by 

 Opie ('00), Heiberg ('06), and Laguesse ('08), give us an idea of 

 the relative numbers in different parts of the pancreas, but the 

 results obtained by Laguesse by the more laborious method of 

 reconstruction of single lobules indicates that the real number is 

 probably much in excess of that obtained in such counts. When 

 we apply the method of counting islets in sections to the investi- 

 gation of the question whether the number of islets has been 

 increased by this or that experimental procedure, we at once intro- 

 duce a new source of error, for it is obviously impossible to exam- 

 ine and count the islets in a complete series of sections of the whole 

 pancreas, and if we examine only selected portions of the pancreas 

 our results are open to the objection that the part so selected may 

 not be representative even of the region from which it has been 

 taken, for the results of Laguesse and others indicate that there 

 may be wide variations in the relative number of islets even in 

 adjacent pieces of the pancreas. 



