412 Cytology of the Areas of Langerhans 



well as others) observed the fact that the cells of the islets contained 

 granules which could not be considered as artifacts, but were properly 

 to be regarded as products of the metabolism of the cells themselves. He 

 argues that the granules are not artifacts because 



. (a) The cells are literally crowded with brilliantly stained (safranin 

 or gentian violet) granules. 



(b) In the living structure the granules are also present when examined 

 in serum. 



(c) They are analogous (1) in their arrangement, (2) in their refrac- 

 tion, (3) in their brow T n coloration with osmic acid, and (4) in their vivid 

 red coloration with safranin, to zymogen granules, and 



(d) They are soluble in acetic acid. 



Considering these facts in connection with the results of his histo 

 genetic study of the islets in the pancreas of the sheep, he concludes that 

 the islet and the acinous cells are transformable one into the other, as 

 he gathers, also, from his studies of the embryo sheep alone. He believes 

 that the islets normally furnish an internal secretion to the pancreas, but 

 have the property of alternation from internal to external secretion, the 

 former predominating. In the viper there are (1) secondary islets, 

 scattered throughout the gland; developed from acini they return again 

 to acini; and (2) permanent islets which, developed directly from the 

 embryonic pancreatic tubes and not from acini, have no tendency to 

 transformation into acini. But in the sheep they are atrophied, for the 

 greater part, at a certain stage in their development, and are eliminated ; 

 in the viper they tend to persist to maturity. Laguesse finds vestiges of 

 lumina among the cell-cords of the islets in vipers. From the above it will 

 be seen that Laguesse coincides (with certain modifications) with the 

 speculation of Lewaschew. 



Flint (5) has studied the islets with a view of demonstrating the 

 presence of a reticular capsule, and De Witt (3), in the course of an 

 important experimental study of the islets, has constructed very handsome 

 models of these structures showing their structural independence, and has 

 furnished experimental evidence of the presence in the islets of the acti- 

 vator substance of Cohnheim. 



The presence of granules in the islet cells was observed, as we saw 

 above, by Laguesse; and Diamare (4) called attention to large granular, 

 deeply staining cells in the islets of the rabbit's pancreas. W. Schulze 

 (20) called attention to similar cells in the islets of the guinea pig's 

 pancreas, and Mankowski (12), who repeated Schulze's work, found that 

 on ligature of the pancreas the epithelial elements disappeared. Man- 

 kowski, however, found that an injection of silver nitrate disclosed certain 



