CHAPTER XXXIV. 459 



There is this difference, that the impregnated material cannot 

 be preserved for any length of time in alcohol and must not remain 

 in it for more than one or two days. But it may be kept in the 

 silver solution until wanted for sectioning. According to 

 v. GrEHUCHTEN (La Cellule, vi, 1890, p. 405) pieces may be kept with 

 advantage for many days, weeks and months in the silver nitrate 

 solution. An abundant impregnation was found by him after many 

 days up to six months where almost none had been seen after 

 twenty-four to forty-eight hours only. But the material must be 

 kept in the dark. 



As to the proper duration of the hardening process in different 

 cases, it must be pointed out that definite rules can hardly be given, 

 while investigators can easily find out the right moment for success- 

 fully transferring the pieces into the silver bath by means of attempts 

 made in accordance with the purpose in view and the quality of the 

 material with which they are working. However, the following 

 points should be borne in mind : 



Spinal cord of chick from the sixth to the tenth day of incubation 

 twelve to forty-eight hours in the hardening mixture (up to the fifth day 

 the embryos may be treated whole, later the vertebral column should be 

 dissected out and cut into two or three segments ; it need not be 

 opened). The spinal column of newborn rats and mice should be treated 

 in the same way, and remain in the mixture for twenty-four hours for 

 spinal ganglia, or for two to six days for the cord itself. The encephalon 

 of these subjects may be treated in just the same way, without being 

 dissected out. 



v. LENHOSSEK (op. cit.) recommends for human fatal cord two to three 

 days for neuroglia, three to five for nerve-cells, and five to seven for 

 nerve-fibres and collaterals. 



Cerebellum of new-born subjects three to five days in the hardening 

 mixture. 



Cerebral cortex of young subjects two to three days (mice), or as long 

 as five (rabbit, cat) ; cortex of adults, eight to fifteen days. The most 

 favourable region of the brain is the Ammon's horn, especially in the 

 rabbit. 



Retina twenty-four to forty-eight hours in the mixture, then 

 " double " impregnation ( 923). 



Sympathetic. SALA, L. (Mon. Zool. Ital., iii, 1892) found the 

 inferior cervical ganglion particularly suitable for staining by Golgi's 

 rapid process. He proceeds thus: osmium bichromate mixture, 

 three days ; quick wash in distilled water ; silver bath, two to three 

 days ; further wash in distilled water and passage into the same osmium- 

 bichromate mixture for about four days ; a third impregnation can be 

 resorted to, in which case pieces should remain in the hardening fluid 

 for five to seven days. 



Spinal cord of larvw of Amphibia. The entire larvae (best 2 to 2-5 cm. 



