STUDIES ON THE PANCREAS OF THE GUINEA PIG 327 



pancreas of a guinea pig after a period of eight to ten hours dis- 

 charges its zymogen so completely that only a few cells show any 

 zymogen granules. Indeed, I have uniformly secured by the 

 subcutaneous method in guinea pigs a more complete discharge 

 of the zymogen granules than I have ever been able to secure in 

 dogs by the intravenous method associated w^ith frequent with- 

 drawals of blood recommended by Dale ('05). 



The secretin for these experiments was obtained from fasting 

 dogs by a uniform technique, using 2 cc. of 0.4 per cent, solution 

 of hydrochloric acid to extract each gram weight of scraped mu- 

 cous membrane. The solution was filtered and kept slightly acid, 

 and rendered faintly alkaline at the time it was injected. Fresh 

 secretin solution was employed for each day's experiments. 



The discharged pancreases obtained by long stimulation with 

 secretin are very favorable for total counts by the neutral red 

 method. The blood vessels are dilated and the pancreas injects 

 well and quickly, and overstaining or incomplete staining is rare. 

 The islets stain as strongly as they do in the resting pancreas, 

 the granule content of their cells being apparently unaffected by 

 secretin. Furthermore, the absence of zymogen granules makes 

 the lobules unusually transparent, enabling one to see even 

 the smallest islets with ease, and so permitting accurate counting. 



The first series of experiments was conducted without carrying 

 parallel controls, because I thought that if the increase of islets 

 were so great as to be easily apparent to one using the haphazard 

 section method of estimation, the total number after exhaustion 

 should so far exceed the maximum of the normal counts as to 

 leave no doubt of the issue. This first series, however, while 

 showing uniformly high counts in the secretin experiments, were 

 yet all well below the maximum for resting pancreases of animals 

 of the same range of weight. Furthermore, while the counts 

 tended to be favorable to Dale's claims the islets were just as 

 sharply defined from the acinus tissue as in the normal animals 

 which had been previously counted. Around the margins of the 

 islets there were no cells showing only a few islet granules. All 

 cells showing granules at all were packed full of them and the other 

 cells, acinus, centroacinary and duct cells contained no islet gran- 



