STUDIES ON THE PANCREAS OF THE GUINEA PIG 



367 



osmic bichromate, and staining in acid fuchsin with differentia- 

 tion in picric acid best. In these preparations, the B granules 

 remain unstained while the A cells stain intensely red. For the 

 B cells alone the method recommended by Lane is best. 



For the nuclei and chromophile substances I have used toluidin 

 blue and other basic dyes without counterstain. 



In preparations in which the granules of the islet cells are not 

 preserved or in which they remain unstained, the protoplasm 

 exhibits an extremely fine alveolar structure, which I believe to 



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Fig. 12 Small portion of an islet of Langerhans of the guinea pig. Shows 

 B cells filled with fine granules, and A cells stained diffusely; a, A cells. X 1066. 



be due to the same cause which produces the coarse alveolar struc- 

 ture in the inner zone of the acinus cell, namely, the alveolae rep- 

 resent granule-holding spaces. In badly fixed material a coarser 

 alveolar structure maybe seen which is due to post mortem changes 

 in the cell which I have described above as appearing slowly in 

 cells studied in salt solution. 



When the specific granules of the cells are stained they present 

 the appearance shown in fig. 12. The protoplasm is studded with 

 fine granules, which are imbedded in an apparently homogeneous 

 ground substance. 



