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 brown 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 histe- 
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 
