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-subli- 

 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 most 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 Fixed 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 



