CHAPTER XVII. 207 



reduction. Objects, therefore, should always be so thin that light 

 can readily stream through them. He impregnates for a few hours 

 in 1 per cent, gold chloride ( 361) 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 all sides, and exposed to diffused 

 daylight in summer, or direct sunlight in winter, for six to eight 

 hours without a break. 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 ( 343). He finds 

 such preparations absolutely permanent. 



Post- Impregnation . 



369. GERLACH'S Method (STRICKER'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, and after ten to twelve hours 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 

 dehydrated and mounted in balsam. 



See further, for Nerve Centres, under " Nervous System." 



370. GOLGI (Mem. Accad. Torino [2], xxxii, 1880, p. 382) puts 

 tissues previously hardened in 2 per cent, solution of bichromate of 

 potash for ten to twenty minutes into 1 per cent, solution of arsenic 

 acid, then into | per cent, solution of chloride of gold and potassium 

 for half an hour, washes in water, and reduces in sunlight in 1 per 

 cent, arsenic acid solution, which is changed for fresh as fast as it 

 becomes brown. Mount in glycerin. Sunny weather is necessary. 



371. APATHY'S Method (Zeit. wiss. Mik., x, 1893, p. 349; Mitth. 

 Zool. Stat. Neapel, xii, 1897, p. 729) : The material to be used must 

 have been fixed either in sublimate or in a mixture of equal parts of 

 saturated solution of sublimate in 0-5 per cent, salt solution and 

 1 per cent, osmic acid (this more particularly for Vertebrates). The 

 material should be imbedded as quickly as possible, either in paraffin 

 or in celloidin. Sections are made and fixed on slides, and after 

 the usual treatment with iodine, etc., are either put into distilled 



