AND HOW TO USE IT. 105 



chromic acid, which is changed for fresh on the fourth day. A 

 few days later (when the cord appears hard), the chromic acid is 

 removed by means of water and the cord put into spirit, followed 

 by absolute alcohol, which must be twice changed. Now imbed 

 in paraffin ; pass sections either (a) through alcohol, carmine, oil 

 of cloves, into Canada balsam ; or {d) simply through benzole or 

 Bromier's " Flochwasser " and Canada balsam. (" Flochwasser " 

 appears to me to be a preparation of xylol.*) 



Bichromate and Silver Nitrate Process.— This is sometimes 

 spoken of as Golgi's method, and is taken from a paper of 

 Rezzonico, a pupil of Golgi.t 



I. — Take pieces of perfectly fresh spinal cord and soak them 

 in a 2 per cent, solution of bichromate of potash for a varying 

 period, according to temperature. (In summer eight to fifteen 

 days may suffice ; in winter about a month is necessary.) 



2. — Wash them, put in a 075 per cent, solution of nitrate of 

 silver. Time varies according to temperature. In summer the 

 reaction is complete throughout the tissues in two or three days ; 

 in winter, eight to ten days. 



3.— Dehydrate small pieces in alcohol (make sections if neces- 

 sary), clear in oil of turpentine. Tease while in the turpentine 

 and mount in dammar. 



4. — Leave preparations to themselves, in order that the 

 secondary impregnation may take place. In direct sunlight, eight 

 or ten days ; in diffused sunlight, twenty to forty days will be 

 required. Greater certainty is obtained by treating the fresh 

 tissues with osmic acid (by means of interstitial injection) before 

 putting into bichromate. In this case, a much shorter immersion 

 in bichromate will suffice (four to eight days). 



By this method may be seen, in the medullated fibres of the 

 spinal cord, a chain of conical funnels, set one within another, 

 embracing the axis cylinder with their narrow aperture, etc. 



Xylol for Central Nervous System (Merkel's Method.*) — 

 Dehydrate sections from system with 94 per cent, of alcohol, in 

 which they should remain ten minutes at least ; then clear with 



*"Archiv. fiir .Mikros. Anatom." (1887). 



t " Archivis par le Scienze Mediche." 



