414 Cytology of the Areas of Langerhans 
a pad, and two methods of differentiation were used. In the first method 
the slide, instantly after blotting, was douched with absolute alcohol from 
a medicine dropper to dissolve the excess of the stain, the alcohol quickly 
blotted off, and the sections instantly covered with oil of cloves. The 
differentiation was then watched under the microscope until the zymogen 
granules in the acinous cells were seen to be fairly discrete, the violet 
stain being differentiated out of the cytoplasm which, with this method, 
retains the brownish-yellow of the orange G. In the second method the 
sections were quickly blotted, as before, and the differentiation done with 
acetone (dimethylketone). The sections were douched with acetone from 
a medicine dropper, quickly placed under the microscope, and when 
the zymogen granules appeared, as before, the slide was placed in xylol. 
Xylol was also used for the final clearing of the alcohol-differentiated 
sections. The sections were then mounted in Canada balsam. 
CHEMICAL CHARACTERS. 
The first sections examined were those fixed in alcohol-chrome-subh- 
mate. This fixation is an admirable precipitant of the zymogen granules 
in the pancreas cells, but it has the disadvantage of shrinking the tissues 
somewhat. The granules of zymogen in the acinous cells are discrete and 
handsomely stained by the dye. The islet cells are somewhat shrunken, 
the majority of them taking up the yellow of the orange G. In the center. 
of the islet, sometimes eccentrically placed, and seldom near the edges, 
were seen a number of conspicuous and brilliantly violet cells, apparently 
much larger than the remaining cells of the islet and must frequently 
seen in a sharply defined group (Fig. 1). They seldom appear scattered - 
or isolated. Examined with powers which distinctly show the individ- 
uality of the zymogen granules, the large violet cells of the islet appear 
to be of a diffuse color; but when examined under 2 mm. apochr. these 
cells are found to be filled with granules very much smaller than the 
zymogen granule of the pancreas, but quite distinct none the less. The 
nuclei are large and vesicular, and at times surrounded by a very narrow 
clear zone in which there is seen occasionally a centrosome. The remain- 
ing cells of the islet, considerably more numerous than the cells reacting 
to the violet stain, show no granules in the cytoplasm, are smaller than 
the granular cells, and present other morphological characters which 
differentiate them from the latter. I will recur to these matters presently. 
Preparations Fiaed in 70 Per Cent Alcohol.—The presence of granules 
in certain of the islet cells, simultaneous with the presence of similarly 
reacting granules of zymogen in the acinous cells, suggested the query 
