STUDIES ON THE PANCREAS OF THE GUINEA PIG 305 



mating the total number in the pancreas, because the total reduc- 

 tion of the dj^e in the acinus tissue to a red safranin and the 

 resulting color contrast eliminates for these pancreases the diffi- 

 culty due to the staining of the zymogen granules. 



2. Vital staining methods for demonstrating the ducts and their 



relation to islets and acini 



a. Pyronin method for demonstrating the ducts. Pyronin having 

 relatively less color value than the preceding dyes is used in a 

 higher concentration for vital staining. A 1-1000 solution in 

 isotonic salt solution is employed and injected from the aorta as 

 described in methods 1 and 2. It may be combined with neutral 

 red, janus green, or methylene blue, in the same solution, thus 

 giving, by reason of the different selective affinities of the dyes, 

 double vital stains. The pancreas stained with pyronin alone 

 takes on a light rose tint, and pieces of such a pancreas mounted 

 in salt solution under a cover show intensely red stained duct 

 cells including the whole duct system of the pancreas from the 

 main duct to the last centroacinous cell. The islets stain faintly 

 rose color with pyronin, but the stain is not sufficiently intense 

 to permit of an accurate demonstration of the relations of islets 

 and ducts. For this purpose it is necessary to make a double 

 stain with pyronin and neutral red or with pyronin and janus green. 

 In the former case the islets come out deep yellow red, the ducts 

 rose red, and it is possible in such a preparation to determine accu- 

 rately in a simple mount in salt solution, which are duct cells, and 

 which are islet cells. In the double stain with pyronin and janus 

 green, however, the contrast is very striking for every islet cell is 

 stained the characteristic slate blue of the janus green, while every 

 duct cell or centroacinus cell is stained the deep rose red of the 

 pyronin. Ganglion cells of the sympathetic ganglia and nerves 

 also stain rose-red in pyronin. 



b. The methylene blue method for the demonstration of the ducts. 

 Inject from the aorta with a one in 10,000 solution of methylene 

 blue in isotonic salt solution until the pancreas has a uniform blue 

 tint. Successful preparations are those in which the blue pene- 



