Nerve Cells and Fibers 199 



staining: 



1. Dry pieces of tissue with filter paper, place in 0.75% aqueous silver 

 nitrate (0.75 gm./lOO ml. water): 24-48 hours. If solution turns 

 yellow, renew it. 



2. Transfer to 40% ethyl alcohol, several changes: 1-2 hours. 



3. Transfer to 80% and 90% alcohol: 1 hour each. 



EMBEDDING and SECTIONING: 



1. Dehydrate in absolute ethyl alcohol: 12 hotns. 



2. Transfer to absolute alcohol-ether (1:1): 2-4 hours. 



3. Infiltrate with 4% celloidin or nitrocellulose: 1-2 days. 



4. Embed and cut thick sections, 20-25 microns, or more if desirable. 



mounting: 



1. Wash sections carefully in 80% alcohol to remove excess silver. 



2. Dehydrate in absolute alcohol: few minutes. (Add few ml. chloro- 

 form to absolute alcohol to prevent loss of nitrocellulose.) 



3. Clear in clove oil, terpinol, or the like. 



4. Mount on slides, press with filter paper. Add a drop of thick 

 mounting meditun. Warm to drive off solvent and just before resin 

 cools, add cover glass. 



results: 



nerve cells and processes — deep black 

 backgrotmd — light yellow 



comments: 



If tissue has been fixed in 10% formalin, blot off excess formalin and 

 chromate for 1-2 days, room temperature, in one of the following 

 fluids (Davenport and Combs, 1954). 



1. potassium dichromate, 5% aqueuos 100.0 ml. 



glacial acetic acid 6.9 ml. 



2. zinc or cadmium chromate 1.5 gm. 



distilled water 25.0 ml. 



glacial acetic acid 6.0 ml. 



when chromate has dissolved, add: 



potassium dichromate, 5% aqueous 65.0 ml. 



3. potassium dichromate, 3.0 gm. 



potassium acetate, anhydrous 1.8 gm. 



distilled water 100.0 ml. 



4. A. cadmium nitrate (4H2O) or zinc nitrate 



(GHoO) 3.0 gm. 



distilled water 25.0 ml. 



