SPECIAL NEUROLOGICAL STAINING METHODS 37 



{d) Formalin-bichromate MctJiod. — Tissues are placed for from two 

 to six days in the following solution: 



Formalin, lo to 20 parts. 



Potassium bichromate, 3-per-cent. aqueous 



solution, 90 to 80 parts. 



Subsequent treatment with silver is the same as in the previously 

 described method. The results resemble those of the slow method. 

 The specimens may be kept in strong alcohol. The method is satis- 

 factory only for the adult cerebrum and cerebellum. 



(2) GoLGi BiCHLORiD METHOD. — Material, which need not be 

 cut into small pieces, remains for several months in the potassium- 

 bichromate solution (see Slow Silver Method), after which it is 

 transferred to a 0.25-per-cent. to i-per-cent. aqueous solution of 

 mercuric chlorid for from four to twelve months or longer, the 

 solution being changed as often as discolored. The degree of impreg- 

 nation must be determined by frequently testing the material, but is 

 usually indicated by the appearance of small white spots on the sur- 

 face of the tissue. 



A modification of the bichlorid method, known as the Cox-Golgi 

 Method, often gives good results. The following fixing solution is 

 used: 



Potassium bichromate, 5-per-cent. aqueous solution, 20 parts. 

 Mercuric chlorid, 5-per-cent. aqueous solution, 20 parts. 



Distilled water, 40 parts. 



After mixing the above, add 



Potassium chromate, 5-per-cent. aqueous solution, 16 parts. 



Tissues remain in this fluid for from two to five months. 



In the Golgi silver methods the result of the treatment, first with 

 bichromate and then w^th silver nitrate, is that a precipitate is formed 

 in the tissue, a chromate or some other silver salt, which in favorable 

 cases is largely confined to certain of the nerve cells and their proc- 

 esses. It must be remembered that only a few of the cells and proc- 

 esses are stained, these often only partially, and that other irregular 

 precipitations are usually present. In the mercury methods, the 

 bichromate of potassium and the bichlorid of mercury may be used 

 combined in the same solution. There are other modifications of 

 the Golgi methods, in which similar precipitates of other metallic 

 salts are secured. 



