88 Neurological Technique 



F. Differentiating fluid. — 



Ferric chloride (pure), 30 g. 

 70 per cent, alcohol, 100 cc. 



G. Clearing agent. — Origanum oil (oleum origani cretici). 



PROCEDURE. 



1. To fix. — Place pieces of central nervous system, preferably 

 spinal cord, in 20-30 times their volume of 10 per cent, formalin 

 (A, i), for 4 days or more. Change the fluid after the first day. 

 In the formalin solution the tissue may remain indefinitely and 

 pieces taken when desired. Keep the vessel closed. 



2. Transfer small pieces (2-5 mm. thick) to 15-20 volumes 

 of the saturated picric acid solution (A, 2) and let remain for 

 4 or 5 days. 



3. Rinse off surplus picric acid quickly in distilled water, and 

 then place the pieces in 30-40 volumes of the 5 per cent, 

 ammonium bichromate (B) and keep at a temperature of about 

 38° C. for 4 days. 



Change the solution at the end of 24 hours to avoid the 

 effects of precipitation. 



4. Wash in distilled water, 5-10 minutes. 



5. Transfer to 70 per cent, alcohol for y^ hour. 



Thence dehydrate, imbed in celloidin, and section as directed in 

 X, 3, 4, and 5, p. 64. Cut the sections as thin as the size of the 

 piece will allow (5-15 /^). 



6. Withdraw the 70 per cent, alcohol from the sections and 

 replace it with 50 per cent, for 5 minutes. Then replace 50 per 

 cent, alcohol with distilled water for 5-10 minutes. 



7. Replace the water with the potassium permanganate solution 

 (C) for 15-20 minutes. 



8. Wash in distilled water, 1-3 minutes. 

 The sections are now a dark brown. 



9. Replace w^ter with the oxalic acid solution (D) for 20-30 

 minutes. 



This converts the color into a light brown. 



10. Wash in two or three changes of distilled water for 5-10 

 minutes. 



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