CHAPTER XXXII. 439 



tised animal, passes a needle in the subarachnoid space, and allows 

 the fixative to flow in "under a gravity pressure of 75 cm." The 

 heart stops about a minute after the beginning of the injection, 

 which is continued for twenty hours. At the end of this time the 

 cord is removed, pieces cut and dropped directly into the silver bath. 

 For counterstaining Penfield finds it particularly useful to immerse 

 untoned sections into a diluted solution of Unna's polychrome- 

 methylene blue for one to four hours, this being followed by passage 

 through alcohols of increasing strength and differentiation in absolute 

 alcohol. By this method, also Holmgren's, trophospongium is 

 sometimes stained. But for the study of the relationship between 

 the latter and Golgi's apparatus, Penfield (in litteris) prefers to make 

 drawings of the apparatus from certain selected cells, subsequently 

 removing the coverslip and bringing the slides through graded 

 alcohols into 5 per cent, iron alum for twelve to twenty-four hours. 

 This removes all silver from the cells as well as the counterstain, and 

 at the same time mordants the tissues for further staining by Heiden- 

 hain's iron-hsematoxylin method. If the proper amount of diffe- 

 rentiation has been secured of the particular cells already drawn, the 

 trophospongium will be found stained with great detail. 



Addendum. 



HOLMGREN'S Method for Trophospongium.^ Fix small pieces or 

 ganglia in trichlorolactic acid for twenty-four hours. Dehydrate 

 and embed in paraffin as usual. Stain thin sections for twenty-four 

 hours in Weigert's resorcin fuchsin solution for elastic fibres (see 

 758) recently prepared and a little diluted. Dehydrate and mount 

 as usual. 



D. Methods for the Demonstration of the Sustaining Apparatus 

 of Medullary Sheaths, Neurokeratin, etc. 



850. Methods demonstrating Funnels and Spiral Filaments. 



GOLGI (see EEZZONICO, Arch. p. 1. Sc. Med., iv, 1880, p. 78 ; GOLGI, 

 Opera Omnia /, p. 163) puts small pieces of spinal cord in 2 per 

 cent, potassium bichromate for eight to fifteen days in summer, or 

 a month in winter. After a quick wash he transfers them into 

 -50 to -75 per cent, silver nitrate for two or three days in summer, 

 or eight, ten or more in winter. The pieces are then washed in 

 95 per cent, alcohol, dehydrated in absolute alcohol, cleared in oil 

 of turpentine and teased therein. The preparations, mounted in 

 dammar, must be exposed to sunlight for eight to ten days ; or to 

 diffused daylight for twenty to forty days. 



