416 CHAPTER XXXII. 



cover. Preparations mounted under covers in the usual way 

 always go bad sooner or later, whilst those that are mounted 

 without a cover keep very well, especially if they be kept in the 

 dark. GOLGI states that he has a large number that have 

 kept without change for nine years. 



The order in which the elements of tissues impregnate is 

 first, axis-cylinders, then ganglion cells, and lastly neu- 

 roglia cells. 



745. GOLGI' s Bichromate and Nitrate of Silver Method, 

 RAPID Process (op. cit., p. 33). Small pieces of very fresh 

 tissue are thrown into the following mixture : 



Bichromate solution of 2 to 2' 5 per cent. 



strength . . , . .8 parts. 



Osmic acid of 1 per cent, strength . 2 



The hardeniog being much more rapid than with the 

 slow process, the tissues will begin to be in a fit state for 

 taking the silver impregnation from the second or third 

 day ; in the next following days they will be in a still more 

 favourable state, but the favourable moment does not last 

 long ; the faculty of impregnation soon declines, and is gene- 

 rally quite lost by the tenth or twelfth day. 



The silver impregnation is conducted exactly as in the 

 slow process, and sections are prepared and mounted in the 

 same manner. 



There is this difference, that the impregnated material 

 cannot be preserved for any length of time in alcohol, but 

 must not remain for more than two days in it. But it may 

 be kept in the silver solution until wanted for sectioning*. 



This process has the advantage of great rapidity, and of 

 sureness and delicacy of result, and is the one that has 

 found the most favour with other workers. But for 

 methodical study of any given part of the nervous system, 

 G-OLGI himself prefers the following : 



746. GOLGI'S Bichromate and Nitrate of Silver Method, 

 MIXED Process (op. cit., p. 34). Fresh pieces of tissue 

 are put for periods varying from two to twenty-five or 

 thirty days into the usual bichromate solution. Every two 

 or three or four days some of them are passed on into the 

 osmio-bichromate mixture of the rapid process, hardened 



