368 R. R. BENSLEY 



The mitochondria of the islet cells may also be seen in the prep- 

 arations fixed in acetic osmic bichromate and stained with acid 

 fuchsin, etc., for though the granules of the cell are stained by this 

 method they remain sufficiently transparent so that one can see 

 the more intensely stained mitochondria among them. The latter 

 differ markedly from the mitochondria of the acinus cells though 

 they have the same staining characters. In the islet cells the 

 mitochondria is in the form of delicate filaments and granules 

 scattered throughout the cell, though there is often a slight con- 

 centration of them in the base of the cell near the blood-capillary. 



The canals of Holmgren resemble those of the acinus cell both 

 in topography and location for, while at first sight it seems as if 

 the networks were located indifferently on the capillary or other 

 side of the nucleus, when a column of cells composed of two layers 

 is found cut through the center, the canals are invariably found on 

 the side of the nucleus farthest from the capillary. In the islet 

 cells the canals form a more open network than in the acinus cell, 

 and processes more frequently extend around the nucleus in the 

 direction of the capillary. 



The two kinds of cells of the islet are distinguished from one 

 another by the staining properties of their granules and by nu- 

 clear characters. The former differences I have already indicated. 

 The nuclei of the A cells are oval in outline and much less rich in 

 chromatin than the acinus cells and B cells. The nuclei of the B 

 cells are spherical or slightly oval, and contain large chromatin 

 granules. Both A and B cells lack the large eosinophile nucleo- 

 lus which the acinus cell possesses, though smaller eosinophile 

 bodies may be often observed. 



When studying the cells of the islet by methods which demon- 

 strated the one type to the exclusion of the other, as for example, 

 by the methods of Lane it seemed as though the two types de- 

 scribed included all of the cells of the islet. As soon, however, as 

 it became possible to stain the two types differentially in the same 

 preparation it became apparent that there were, in the islet, 

 cells which contained neither A granules or B granules. In the 

 acetic osmic bichromate preparations, stained as described above, 

 these cells stand out as clear cells with numerous rather coarse 

 mitochondrial filaments. Their nuclei resemble those of the A 



