312 RETINA, INNER EAR, NERVES. 



3. Dehydrate small pieces with alcohol (make sections if 

 necessary), clear in oil of turpentine, tease in the turpentine, 

 and mount in dammar. 



4. The preparations are then left to themselves in order 

 that the secondary impregnation may take place. In direct 

 sunlight, eight to ten days will complete the process; in 

 diffused daylight (or in the dark ?), twenty, thirty, or forty 

 days. 



A somewhat greater precision of the reaction is obtained by 

 treating the fresh tissues with osmic acid (by means of inter- 

 stitial injection) before putting them into the bichromate. 

 In this case a much shorter immersion in the bichromate will 

 suffice (four, six, or eight days). 



By this means may be demonstrated in the medullated 

 fibres of the spinal cord a chain of conical funnels, set one 

 within another, and embracing the axis cylinder with their 

 narrow aperture, and the external surface of the following 

 funnel with their greater aperture ; and it is seen that they 

 consist of a fine spiral fibre wound into the form of a funnel. 

 (The appearance of rings and strainers is due to imperfect 

 action of the silver.) 



(2) For the Study of Peripheral Nerves Golgi modifies the 

 process as follows (1. c., 1879, p. 238) : 



1. Pieces of nerve are immersed in the bichromate solution 

 for from four, six, or eight hours to one day, or at most two 

 days. 



2. From time to time pieces are removed into the nitrate 

 of silver ; they remain there for from twelve to twenty-four 

 hours. 



3. They are washed with several changes of alcohol. 



4. Tease in the alcohol, dehydrate, clear with turpentine, 

 mount in dammar. 



5. Reduce in direct sunlight ; in summer a few days suffice, 

 in cold weather some weeks are necessary. 



Does not give quite such fine results as the osmium bichro- 

 mate silver method next to be described, but the preparations 

 keep indefinitely. 



(3) The Osmium, Bichromate, and Silver Method (ibid., p. 237). 

 A perfectly fresh piece of nerve is thrown into the following 

 liquid : 



