256 CHAPTER XVIII. 



having the objects thoroughly penetrated by light from all 

 sides during the process of reduction. Objects, therefore, 

 should always be so thin that light can readily stream 

 through them ; they should either be membranes or sections. 

 They should be either stretched out (e.g. on a slide) or hung- 

 up in the reducing bath in such a way as to be lighted from 

 both sides. He impregnates for a few hours in 1 per cent, 

 gold chloride ( 347) in the dark, then brings the objects 

 without washing out with water, the gold solution being- 

 just superficially mopped up with blotting-paper, into 1 per 

 cent, formic acid. They are to be set up in this, in a tube 

 or otherwise, so that the light may come through them from 

 <(ll sides, and exposed to diffused daylight in summer, or 

 direct sunlight in winter, for six to eight hours without <t 

 1/reak. They must not be moved about more than can be 

 helped in the acid. If the acid becomes brown it may be 

 changed for fresh. The temperature of the acid should not 

 be allowed to rise over 20 C., whence direct sunlight is to 

 be avoided during the summer. He mounts in glycerin 

 or his syrup ( 328). He finds such preparations absolutely 

 permanent. 



B. After gilding. 



356. GEULACH'S Method (STEICKER'S Handb., 1872, p. 678) : 

 Spinal cord is hardened for fifteen to twenty days in a 

 1 to 2 per cent, solution of bichromate of ammonia. Thin 

 sections are made and thrown into a solution of 1 part of 

 double chloride of gold and potassium to 10,000 parts water, 

 which is very slightly acidulated with HC1. They remain 

 there from ten to twelve hours, and having become slightly 

 violet, are washed in hydrochloric acid of 1 to 2 : 3000 

 strength, then brought for ten minutes into a mixture of 1 

 part HC1 to 1000 parts of 60 per cent, alcohol, then for a few 

 minutes into absolute alcohol, and thence into clove oil, for 

 mount ing in balsam. 



(See further, for Nerve Centres, under " Neurological 

 Methods.") 







357. GOLQI (Mem. Accad. Torino [2], xxxii, 1880, p. 382) 

 breats ti^nes previously hardened in 2 per cent, solution of 



