Electron Microscopy 399 



stable film than celloidin, but the solutions deteriorate rapidly unless 

 kept in the refrigerator. 



The grids are tiny and are most easily handled with stainless steel eye 

 forceps. The forceps tips can be bent slightly and sharpened with fine 

 emery paper for a delicate grip. Forceps with the bottom jaw sharpened 

 to a knife-edge will help to lift grids from a flat surface {Hall, 1953). 



Fixation 



In order to increase the scattering of electrons, the density of the speci- 

 men must be increased — some sort of reagent must be applied to it. For 

 these so-called "electron stains" chemicals of high atomic number have 

 been tried, compounds of heavy metals (tungsten and osmium in par- 

 ticular) using phosphotungstic acid and osmic acid. Pease and Baker 

 {1950) concluded that osmic acid was the "outstanding" fixative. Lujt 

 {1956) used potassium permanganate for membrane systems in partic- 

 ular. 



Osmic Fixation 



In this method, 1-2% osmic is buffered Avith either I or II below, pH 

 7.4: 



solutions: 



I. Edwards et al. {1956); Palade {19'>2): 



0.1 4M sodium acetate and sodium veronal .... 5.0 ml. 



O.IN HCl 5.0 ml. 



1-2% osmic acid 12.5 ml. 



With distilled water make up to 25.0 ml. 



II. Sjostraud {1956): 



Buffer solution A : 



sodium acetate 9.714 gm. 



sodium veronal 14.714 gm. 



distilled water 500.0 ml. 



Btiffer solution B: 



sodium chloride 40.25 gm. 



potassium chloride 2.1 gm. 



calcium chloride 0.9 gm. 



distilled water 500.0 ml. 



