330 R. R. BENSLEY 



ules. Thus while the counts were favorable to Dale's claims, the 

 examination of the tissue under apochromatic immersion lenses 

 showed no transition forms. Accordingly, I abandoned the 

 method of securing guinea pigs for experiment by purchase 

 from different breeders, and postponed further secretin experi- 

 ments until I could have at my disposal animals bred and reared 

 in the laboratory and so subjected to the same conditions through 

 their whole life. The animals so reared showed a narrower 

 range of variation in numbers of the islets than those previously 

 counted, and the high and low counts were about evenly distrib- 

 uted among the secretin guinea pigs and the controls. Then, 

 to confirm the suspicion that the previous result had been due 

 to the mixed sources from which the guinea pigs had been obtained 

 I made a final experiment with six guinea pigs obtained from 

 sources outside the laboratory. The counts of these animals 

 (series 6) again showed the wide range of variation previously 

 observed but the results were an unequivocal refutation of the 

 claim that secretin stimulation increased the number of islets 

 of Langerhans, because the maximum number was found in one 

 of the control animals and the minimum in one of the secretin 

 animals. Furthermore, two of the secretin animals of this series 

 approached very closely the minimum counts for the whole ninety- 

 nine normal and experimental animals. 



^. The effect of secretin stimulation on the pancreas of the toad 



In his studies on the effect of secretory activity on the pancreas, 

 particularly in reference to the number and size of the islets of 

 Langerhans, Dale made experiments on the toad, in which, by 

 injection of secretin solution into the dorsal lymph sac, it was 

 possible to bring the pancreas to a state of exhaustion, and keep 

 it in this condition for several days. Eleven toads were so treated, 

 and the result according to Dale were the same in all cases, though 

 it varied somewhat in degree. He says: 



There was a very great increase of the tissue, which we have now 

 frequently described, and have called islet tissue. In the specimen, of 

 which a section is reproduced in fig. 11 the change is very extensive. 

 The exhaustion is very complete, no zymogen granules being found in 



