M. A. Lane 415 



whether or not the chromatophile granules of the islet cells were zymo- 

 genic; whether or not the use of a reagent which would be a solvent for 

 zymogen would nevertheless act as a precipitant for the granular substance 

 in the islet cells. This experiment was made with alcohol of 70 per cent 

 strength. Small pieces of pancreas of the guinea pig were fixed, therefore, 

 in 70 per cent alcohol and stained with neutral gentian. In sections 

 treated in this way the acinous cells were quite devoid of zymogen gran- 

 ules except at the extreme edge of the piece, where a partial fixation of the 

 granules was obtained, whereas the islets presented the same appearance 

 as in the sections fixed in the alcohol-chrome-sublimate. The same groups 

 of violet-granulated cells were present. But, as the alcohol had not dis- 

 solved out the prozymogen of the acinous cell, the query still remained 

 whether or not the substance in the islet cell granule partook of the 

 nature of prozymogen. To check this query I applied MacCallum's iron 

 reaction on these sections and failed to bring out the slightest trace of 

 Prussian blue in the suspected cells of the islets, except in the nuclear 

 chromatin. 



Preparations Fixed in Aqutous-Chrome-Sublimate. The use of this 

 fluid I found advisable after exhausting the list of desirable acetic fixations 

 and reducing the quantity of acetic acid to an almost negligible pro- 

 portion. Sections from tissues fixed with an acetic mixture were invar- 

 iably blank as to granules in the cells of the islets. But with tissues fixed 

 in aqueous-chrome-sublimate a most unlooked-for result appeared. The 

 large cells of the islets which had been filled with violet granules in 

 sections fixed with the other fluids were quite free from stained granules 

 in the sections fixed with aqueous-chrome-sublimate, whereas, on the 

 contrary, the cells which gave no violet reaction with the other fluids, 

 in this one were filled with granules of a brilliant violet, while now it was 

 the small groups of large cells that were colored with the yellow-brown 

 of the orange G (Fig. 2). 



From a consideration of these facts several conclusions arise. These 

 conclusions have to do with the microchemistry of the cells of the Islets 

 of Langerhans in the guinea pig's pancreas, and they may be stated 

 somewhat as follows : 



1. The Islets of Langerhans in the pancreas of the guinea pig consist 

 of two types of cells: (a) a type containing a granular substance that is 

 precipitated by alcohol of a strength of from 50 to 70 per cent; and, (b) 

 a type, the granular content of which is precipitated by an aqueous- 

 chrome-sublimate fluid of the general character described. 



2. The granular substance that is precipitated by alcohol is dissolved 



