CYTOLOGICAL STUDIES OF LANGERHANS'S ISLETS 9 



nuclei, etc. These types are designated as a, b, and c. The 

 descriptions are based mainly upon preparations fixed in osmic 

 acid mixtures and stained with acid fuchsin or iron-hematoxylin. 



The specific granules of the a cells (fig. 14) stain heavily, thus 

 giving to the protoplasm a distinctly granular appearance. The 

 cells of this type are of various shapes: cylindrical, pyramidal, 

 polygonal, or even, as often occurs, more or less irregularly 

 shaped, due apparently to pressure from neighboring cells. The 

 nucleus, spherical or polygonal in shape, is provided, in the 

 majority of cases with a thick nuclear membrane which is thrown 

 into folds; the nuclear network is well marked and its meshes are 

 closer than those of the nuclei of acinus cells. 



The cells of b type (figs. 1 to 4, b; 16, 17) are characterized first 

 of all by the fact that their specific granules stain more faintly 

 with iron-hematoxylin than those of the a cells. Like the latter, 

 the b cells are, for the most part, cylindrical or pyramidal in 

 shape, but narrow, elongated cells are not infrequently met 

 with. The shape and structure of the nucleus constitute the 

 second criterion by which these cells may be distinguished from a 

 cells. The nucleus is large and oval in shape, with a smooth and 

 indistinct contour ; the nuclear network, as seen in iron-hematoxy- 

 lin preparations, is represented by indistinct, faintly staining 

 cords or threads on which one or more small nucleoli may be 

 suspended. 



The c cells (figs. 52, 53) contain specific granules which stain 

 even more faintly than those of b cells, and which, in most 

 cases, are not evenly distributed throughout the cell-body, being 

 interrupted here and there by transparent, non-granular proto- 

 plasm, especially at one end of the cell. The c cells are usually 

 smaller than the preceding two types of cells and are either long 

 and narrow or short-cylindrical, pyramidal or even polygonal in 

 shape. The nucleus, irregular in form, is enclosed by a less dis- 

 tinct membrane which may be thrown into folds. The nuclear 

 network is as indistinct as that of the b cell, and the main- 

 nucleolus is likewise small. 



Non-granular cells (figs. 1 to 5, e, 18 to 21), which compose 

 the greater part of the islet elements, contain no specific granules 



