STUDIES ON THE PANCREAS OF THE GUINEA PIG 331 



any part of the section, and a very large proportion of the whole tissue 

 of the gland has undergone the change into islet tissue. . . . Scat- 

 tered in this transitional tissue are several fully formed islets of the rest- 

 ing type which were presumably present before the injection of secretin. 



It was important to test this conclusion of Dale for if it is pos- 

 sible to so transform a large proportion of the tissue of the pan- 

 creas of the toad into true islet tissue, it is hardly worth while 

 expending the energy required to count the islets under experi- 

 mental conditions in mammals. That transformation of pan- 

 creatic tissue into something different was accomplished in Dale's 

 experiments is sufficiently obvious from an examination of his 

 figures, but that the tissue so transformed was really islet tissue 

 is not so clear, for Dale admits that the true islets could be recog- 

 nized' in the midst of the transforming tissue. What then are 

 the clear cells of his preparations? If they are islet cells they 

 should have the normal content of islet cells. 



I have found in confirmation of Dale that the toad is well 

 adapted to this type of experimentation for it is very responsive 

 to secretin solution introduced into the dorsal lymph sac. In- 

 deed, if the dorsal lymph sac of a toad is filled with an active se- 

 cretin solution in the evening, the pancreas will be found next 

 morning so exhausted that the zymogen is reduced to a row of 

 very small granules along the dilated lumen of the acinus. By 

 repeated injections the pancreas may be quite deprived of its 

 zymogen and kept so for several days. If the precaution is taken 

 not to overdistend the lymph sac and to make the injections at 

 frequent intervals, the toad may be kept for as long as seven days 

 with the pancreas in a state of continual exhaustion. Under 

 these conditions, surely, one might expect that the maximum 

 effect of over-secretion would be found. 



The pancreas of the toad, moreover, is well adapted for inves- 

 tigation by the methods of staining the islets of Langerhans by 

 means of neutral red, or janus green. The results obtained here 

 are exactly comparable to those obtained in the mammal, the small 

 granules with which the islet cells are studded taking up the red 

 or the green as the case may be, and permitting an estimate of 

 the total content of islet tissue. 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 12, NO. 3 



