418 Cytology of the Areas of Langerhans 
the substances contained in the granules of the A and of the @ cells are 
chemically different from the substance in the zymogen granule; and are 
different chemically from each other. 
MorRPHOLOGICAL CHARACTERS. 
Coincidental with these chemical differences are found certain differ- 
ences in the morphological characters of the A and £ cells of the islets 
in the guinea pig’s pancreas. The A cell is comparatively large and its 
nucleus is, for the most part, elliptical, although frequently it is circular 
(Fig. 1). It is markedly vesicular, strikingly large and vivid, and its 
chromatin content is very small. The chromatin is distributed in a few 
small, spherical masses, and this contributes, in section, to the lucid, 
vacuous, and prominent appearance of the nucleus of these cells. In 
some of the cells the granules are packed together throughout the entire 
cytoplasm and seem to lie directly against the nuclear membrane. In 
others the granules are determined in a mass bordering closely on the 
capillary, while the remainder of the cytoplasm is comparatively or 
completely free of them. The cells are polygonal and stand out in high 
relief against the lighter and yellowish back-ground formed by the mosaic 
of the 8 cells. This is true only when the stain used is the neutral gentian 
of Bensley. The A cells can be chromatically distinguished only with 
great difficulty when other stains are employed—a fact struck out after 
trying a score or so of different basic dyes. Gentian violet, safranin, 
licht-griin, and other granule stains gave negative chromatic results, 
although the a cells could be recognized by their conspicuous size even 
when the section was treated only with a plasma stain. 
The 8 type of cell appears, as a rule, considerably smaller and is, at 
the same time, vastly more numerous in the islet. Entire cords of them, 
uninterrupted by the presence of the A cells, appear in the picture, and 
almost invariably the cytoplasm of the entire cell is packed with the violet 
granules, which are uniformly distributed around the nucleus and which 
everywhere border on the capillaries. ‘The nucleus of the £ cell is invar- 
iably centrally placed, is smaller than the nucleus of the A cell, circular, 
markedly less vesicular than the nucleus of the A cell, and is also dis- 
tinguished from the nucleus of the A cell by the comparatively large 
quantity of chromatin it contains. In the nucleus of the @ cell the 
chromatin is frequently seen in the form of fine strands forming a net- 
work. In some of the islet cells there were found, indifferently as to 
either kind, a centrosome and, now and then, a mitotic figure. The cyto- 
plasm consists of a delicate network. 
