STUDIES ON THE PANCREAS OF THE GUINEA PIG 353 



islet. In other cases no trace of a duct can be observed. These 

 are, nevertheless, few in number and exceptional. Fig. 4, for 

 example, shows fourteen islets each one of which is directly con- 

 nected to one of the branches of the system of tubules surrounding 

 the duct. 



In his recent article Laguesse ('10) in discussing Dewitt's 

 description ('06) of islets in the interstitial tissue, expresses doubt 

 of their having been composed exclusively of islet tissue and sug- 

 gests that, if continuous series of sections of these islets had been 

 studied, they would have been found to be partly composed of 

 acini. This is, of course, of some importance to Laguesse's 

 theory of balance, for the occurrence of islets with no connection 

 with the acinus tissue would be difficult to reconcile with the view 

 that islets and acini are subject to a constant reciprocal trans- 

 formation. In the preparations stained intra vitam with neutral 

 red it is easy to see that Dewitt's description is correct, and that 

 these islets are composed solely of islet cells. In order, however, 

 to be perfectly sure on this point I have studied these islets in 

 complete series, and found them wholly free from acinus tissue. 

 This is, moreover, what might be expected in view of their origin, 

 for it is apparent that they originate directly from the duct and 

 at no period of their history have any direct relation to acini. 



It will be seen that the observations just described furnish an 

 explanation of the conflicting views of different authors concern- 

 ing the true anatomical relation of the islets of Langerhans to the 

 ducts and to the acinus tissue, for all of the various kinds of rela- 

 tion which have been described actually occur. That the con- 

 nections with the ducts have been so uniformly overlooked is 

 doubtless due to the fact that serial sections have not been studied 

 with sufficient care, and because, even in serial sections, the con- 

 nections are hard to find because they are so small. The failure 

 of the injection method is doubtless due to the fact that the lumina 

 of the ducts going to the islets are filled with a viscid mucus which 

 prevents the injection mass from penetrating to the islet, and 

 that there is no terminal cavity into which this secretion can be 

 backed up. The pyronin method, however, furnishes a means 

 by which any one who may still have doubts about the connections 



