332 R. K. BENSLEY 



The granules may be easily demonstrated in the islet cells of 

 the toad by appropriate methods of fixation and staining. The 

 islets of the toad, like those of mammals, are composed of two 

 types of cells which present similar characters to the correspond- 

 ing cells of the islets of the guinea pig. The B cells, which are 

 the most abundant, show their granules best when fixed in Ben- 

 da's modification of Flemming's fluid, and stained by the mito- 

 chondria method of Benda, or by the neutral gentian method. 

 Under these circumstances the B cells are seen to be filled with 

 minute violet stained granules. The A cells are best demon- 

 strated by fixation in acetic osmic bichromate and staining in acid 

 fuchsin followed by differentiation in solution of methyl green. 

 In these preparations the A cells are seen filled with minute 

 granules stained red, while the B granules remain unstained. 

 After this fixation also the A granules may be stained in safranin 

 or in gentian violet. 



Both the vital stains and the section methods referred to above 

 show that in the pancreas of the toad, particularly in that portion 

 which is near the spleen, there are large numbers of single islet 

 cells located in acini. These are mostly of the A type. None 

 of these methods, however, shows cells containing both the zymo- 

 gen granules and islet granules of either type, nor cells containing 

 only a small proportion of islet granules as might be expected in 

 cells undergoing transformation from one type to the other. 



The pancreases of toads which have been kept for a long time 

 under the influence of secretin, and in which the pancreas is wholly 

 discharged, when examined after vital staining with neutral red, 

 or with janus green, do not differ as regards the islet tissue from 

 normal resting toads. The islets appear to be about as numerous 

 and to present the same variations in size as in the resting pancreas. 

 Nor do the sections made by methods which preserve the granules 

 of the islet cells, and stained by methods which bring out these 

 granules show in the pancreases of toads which have been under 

 continual secretin stimulation for from four to seven days any in- 

 crease in the number of islet cells in the acini nor any general 

 transformation of acinus cells into islet cells. 



The question then arises, what are the cells obtained in large 

 numbers by Dale by this method of experimentation? I cannot 



