224 CHAPTER XVII. 



from all sides, and exposed to diffused daylight in summer, 

 or direct sunlight in winter, for six to eight hours without a 

 t/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 ( 343). He finds such preparations absolutely 

 permanent. 



Post-Impregnation. 



369. GKRLACH'S Method (STACKER'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 J 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. wus. Mik., x, 1893, p. 340; 

 Mitth. Zool. Stat. Neapel, xii, 1897, p. 729). The mate-rial 

 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 



