STUDIES ON THE PANCREAS OF THE GUINEA PIG 349 



islet cells. The islet is thus, notwithstanding its direct connec- 

 tion with the duct, unquestionably a ductless gland, and the duct 

 connections are significant only as an indication of the source 

 whence the islet has been derived. The few cases in which an 

 islet is penetrated by the lumen of its duct are of interest as ex- 

 plaining those cases described by Weichselbaum and Kyrle ('09), 

 where cystic islets have been found as a result of occlusion of the 

 duct. Even the smallest islets on the duct system are solid, that 

 is, the duct does not enter their substance (fig. 9). 



The islets of class 2, namely, those which, though imbedded 

 in the substance of the lobules, yet have no connection with their 

 substance, are apparently islets of the same sort as those which 

 constitute class 1, but which have been surrounded secondarily 

 by acinus tissue. These islets are of interest because, having 

 been secondarily enveloped by the acinus tissue, they are sur- 

 rounded by a thicker and more continuous connective tissue 

 layer than those which have originated within the lobule, and so 

 are responsible for the ideas of those who think that the islets 

 of Langerhans are everywhere separated from the surrounding 

 acinus tissue by a fibrous capsule. 



Class 3 contains the great majority of all the islets of the pan- 

 creas. These islets are located directly in the substance of the 

 pancreatic lobules and are continuous with the ducts and acini 

 of these lobules usually at many points of their surfaces. I have 

 studied the relation of these islets to the other epithelial elements 

 of the lobule both in the freshly stained preparations from pyro- 

 nin and methylene blue injections, and in sections of methylene 

 blue preparations after fixing in ammonium molybdate, etc., and 

 have confirmed the results by the study of serial sections of mate- 

 rial fixed in the acetic osmic bichromate mixture and stained in 

 fuchsin-methyl green, which permits an accurate diagnosis of all 

 the epithelial elements of the pancreas. As a result of these 

 studies I have come to the conclusion that the relations of the 

 islets of this class in the guinea pig are substantially the same as 

 those described for man by Laguesse ('10), with the important ex- 

 ception which I shall discuss more fully later, that I find no tran- 

 sitions between islet cells and acinus cells, and no acini which are 



