STUDIES ON THE PANCREAS OF THE GUINEA PIG 357 



In studying the several components of these cells by fixing and 

 staining methods it is necessary to consider those elements which 

 are visible in the living cell or in the vital stained preparations, and 

 to discard methods of fixation which destroy one or more of 

 these elements, or at the most to use such methods for experimen- 

 tal purposes only. On the other hand, methods which introduce 

 new structures into the cells which are not visible in the living 

 cell must also be discarded. Up to the present, these conditions 

 have usually not been met, as is sufficiently indicated by the 

 almost universal confusion which exists with reference to the identi- 

 fication of the striations observed by R. Heidenhain in the living 

 cell. Many observers identify these with the so-called basal 

 filaments of Solger which are not visible in the living cell, while 

 in reality they are due to the filaments observed by Altmann and 

 Michaelis. The reason for this confusion is that acid fixing 

 fluids are usually employed, which destroy the filaments of 

 Michaelis and Altmann, while they bring to light new filaments 

 which were not visible in the living cell. 



The fluids which I have found to preserve what is present in 

 the living cell without introducing new structural elements by 

 precipitation are as follows : 



1. Benda's acetic-osmic-chromic fluid for the preservation 

 of mitochondria. This, though a poor penetrant, preserves all 

 the elements in the peripheral portions of pieces of pancreas 

 fixed in it, and at the same time permits one to see the effect on 

 the deeper portions of the tissue of the acetic acid which penetrates 

 more rapidly than the other components of the mixture. 



2. The acetic-osmic-bichromate mixture (Technique, 4 d). 

 This mixture has all of the advangates of Benda's fluid, and the 

 additional one that, by appropriate staining, it enables one to 

 differentiate all of the epithelial elements inter se in a single 

 preparation. 



3. Lane's chrome-sublimate mixture. 



4. Formalin Zenker (Technique, 4 c). This is the best fixing 

 solution from the standpoint of penetration, but does not lend 

 itself so well to differential staining as the preceding solutions. 



