500 GOLGI 



I have no experience of the use of creosote or of the mixture, 

 originally proposed by Andriezen, of equal parts of pyridine and 

 xylol instead of the guaiacol, but they should equally well serve 

 the purpose. 



As a general rule one makes sections of 20 to 40 /^i ; thicker 

 sections of 50 to 60 jx, or more, show more than thin ones but do 

 not seem to keejj so well. 



The order in which the elements of nervous tissues impregnate 

 is generally — first, axis-cylinders, then nerve-cells, and lastly, 

 neuroglia cells. 



1028. GoLGi's Bichromate and Nitrate of Silver Method. Rapid 

 Process. Small pieces of very fresh tissues are hardened in a 

 mixture of 2 to 2-5 per cent, potassium bichromate 8 parts, and 

 1 per cent, osmic acid 2 parts. Or, if a very quick hardening is 

 desirable, 2 parts of 3 per cent, bichromate to 1 of 1 per cent, 

 osmic acid. In Golgi's laboratory mixtures of 3 parts of 3 per 

 cent, bichromate and 1 of 1 per cent, osmic acid are generally 

 used. The tissues begin to be in a state suitable for the silver 

 impregnation from the second or third day ; in the next following 

 days they are in a still more favourable state, but this soon declines, 

 and is generally quite lost by the tenth or twelfth day. 



The silver impregnation is conducted exactly in the same way 

 as in the slow process, and sections are prepared and mounted in 

 the same manner, but they should not be left in alcohol for more 

 than an hour or so before mounting. 



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. Gehuchten {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 successfully 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 neiv-born rats and mice should be treated 

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



