M. A. Lane 417 



/? cells both remain unfixed, and the islet appears uniformly brownish 

 yellow. The zymogen granules, on the contrary, appear to be well fixed 

 and react readily to the neutral gentian. 



Aqueous-Chrome-Sullimate plus 5 per cent of 10 per cent cent Nitric 

 Acid. This fixation gives much the same result as that with aqueous- 

 chrome-sublimate,, but the chromatic effects are not so clear. The ft 

 cells are admirably picked out and almost invariably show the entire 

 cytoplasm crowded with granules. In this fluid the zymogen granules 

 are well preserved and take the stain fairly well. 



The affinity of the two types of cells for certain fixing agents is peculi- 

 arly brought out in tissues fixed in a combination of these fluids. Thus 

 in tissues fixed in chrome-sublimate solutions with equal parts of alcohol 

 added, an islet here and there near the edge of the section shows both 

 types of cells equally granulated; and the same is true of islets near the 

 edge of sections from tissue fixed in aqueous-chrome-sublimate to which 

 has been added 5 per cent of 10 per cent nitric acid. 



These various tests, together with those furnished by the use of the 

 three principal fluids above mentioned, enable us to make certain positive 

 statements concerning the nature of the two substances contained in the 

 A and (3 types of cells in the guinea pig's pancreas. That contained in the 

 A cell is fixed by alcohol, by a 10 per cent solution of nitric acid, and by 

 a 10 per cent solution of formol. In all these fixations it is stainable with 

 Bensley's neutral gentian. It is soluble in acetic acid, in saturated 

 aqueous mercuric chloride, in non-alcoholic chrome-sublimate fluids, in 

 these last-mentioned fluids also in the presence of nitric acid, in saturated 

 aqueous picric acid, and in 1 per cent solution of chromic acid. The 

 substance is chemically different from that in the zymogen granules, for 

 in all these solutions the zymogen granule is fixed and remains stainable 

 with neutral gentian, while on the contrary the zymogen granule is 

 soluble in alcohol in which the A granules are well preserved. 



The substance in the granule of the p cell is fixed in aqueous saturated 

 solution of mercuric chloride, in chrome-sublimate fluids in the presence 

 of nitric acid, and in non-alcoholic chrome-sublimate fluids. It is 

 soluble in alcoholic solutions, in acetic acid, in aqueous saturated solution 

 of picric acid, in 10 per cent solution of formol, and in 1 per cent solution 

 of chromic acid. And it differs chemically from the zymogen granule of 

 the pancreas because the latter :s uniformly fixed by the above solutions 

 with the exception of formol, in which it is not completely dissolved but 

 only partially preserved. 



These considerations go to show in contrast to Laguesse's theory that 



