312 R. R. BENSLEY 



the variation in size was so considerable. As the counts pro- 

 gressed, however, it was speedily found that this hope was not 

 justified, and it became necessary to extend the series far beyond 

 what was originally intended. In the records of the earlier counts 

 only the weight of the animal and the total count of islets 

 were recorded. Later, records were kept of sex, pregnancy, total 

 weight of pancreas, and of the weights and corresponding counts 

 of islets in the different portions of the pancreas. The total num- 

 ber of guinea pigs in which total counts of the islets have been 

 made is ninety-nine. Of these sixty-five were normal resting 

 pancreases, twenty-four were from secretin experiments, six from 

 inanition experiments, and four pilocarpine experiments. In view 

 of the fact that the counts offer no support for the claims of 

 Dale ('05) and of Vincent and Thompson ('07) that the number 

 of islets is increased by secretin stimulation and by starvation, all 

 of the counts might well be included in a single table to show the 

 normal range of variation in the guinea pig. I have, however, 

 decided to keep the series separate and offer as normal resting 

 counts only those cases where the animal had been kept without 

 food for twenty-four hours, and in which the secretion had been 

 restrained by atropine. 



It might be supposed that the great differences in total number 

 of islets in different guinea pigs of the same weight would be due 

 rather to the difference in size of the islets than to a real difference 

 in the relative amount of islet tissue present. We have not yet 

 made computations of the relative weights of zymogenic tissue 

 and islet tissue, but it would be quite possible to do this with the 

 neutral red method, and it is hoped that an opportunity will soon 

 be found. It is, however, not the rule that the variation in num- 

 bers is compensated by corresponding variations in size, that is, 

 that, where the numbers are large, the islets are relatively smaller 

 than in the pancreas from an animal of the same weight having a 

 smaller number. On the contrary high numbers are often asso- 

 ciated with a proportionally high content of islet tissue. 



It is, of course, inevitable that the error in such counts would 

 be considerable, owing to the causes to which I have previously 

 referred. Comparative counts made by two different individuals 



