REVIEW OF THE GOLGI METHOD. 77 



mate and of silver nitrate. (3) The method of the combined 

 action of bichromate of potassium or ammonium and bichloride 

 of mercury. (The stain appears black by transmitted, metallic 

 white by reflected light.) 



"(i) The 77iethod of the combined action of bichromate of pot as - 

 siu?n atid of silver nitrate. In the series of methods which I have 

 specially employed this is, in a manner, the fundamental one 

 The others are only variations of this, devised to shorten the time 

 of the preliminary treatment, to make the preparations more 

 stable, to vary the results in various ways, especially to obtain a 

 greater extension of the reaction and to cause the reaction to 

 affect one or another species of the elements or a part of them. 



" I consider it to the point to call attention to the fact that the 

 procedure of the microscopical technique which I will describe, 

 although it rests essentially upon the action of silver nitrate, has 

 nothing in common with the usual method of staining the inter- 

 cellular substance of endothelium, epithelium, and connective 

 tissue, brown or black. In the latter method dilute solutions of 

 silver nitrate are applied immediately to the fresh tissue, exclu- 

 sively to the surface of membranes or membranous tissues of 

 slight thickness (aponeurotic plates, substance of the cornea, intima 

 of vessels), and light exerts an important influence upon the reac- 

 tion whereby the blackening of the combination which the silver 

 salt forms with the ground substance is brought about. With my 

 method the light has nothing to do, and the reaction takes place 

 through the gradual penetration of the silver salt into more or less 

 voluminous pieces which have been previously treated with 

 bichromate. The black-staining of the various elements compos- 

 ing the nervous tissue results from a reducing action which the 

 elements themselves exert, under the influence of the bichromate, 

 upon the silver salt. 



" The procedure necessary to bring about the black-staining of 

 the elements of the central nervous system consists essentially of 

 two parts : — 



" (a) Hardening of pieces in a solution of potassium bichromate. 



" (b) Immersion of the hardened pieces in a solution oj silver 

 nitrate. 



" (a) Hardening in bichromate. Although there are no e-spccial 



