AXES-CYLINDER AND DENDRITE STAINS. 425 



Tliis 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 Golgi himself 

 prefers the following : 



812, GrOLGi's Bichromate and Nitrate of Silver Method, 

 MIXED Process {op. cit., p. 34). — Fresh pieces of tissue ai'e 

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

 days into the usual bichromate solution (§ 810). Every two 

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

 osmio-bichromate mixture of the rapid process, hardened 

 therein for from three or four to eight or ten days, and 

 finally impregnated with silver, and subsequently treated 

 exactly as in the rapid process. 



The reasons for which Gtolgi prefers this process are — the 

 certainty of obtaining samples of the reaction in many stages 

 of intensity, if a sufficient number of pieces of tissue have 

 been operated on ; the advantage of having at one's dis- 

 position a notable time — some twenty-five days — during 

 which the tissues are in a fit state for taking the silver, and 

 the possibility of greatly hastening the process whenever 

 desired by simply bringing the pieces over at once into the 

 osmic mixture ; lastly, a still greater delicacy of result, 

 especially remarkable in the demonstration of axones. 



813. Theory of the Impregnation. — It used to be held that 

 the reaction depends on the formation in the tissues of a 

 precipitate of some salt -of silver. But this seems incorrect. 

 I find (in accordance with Lenhossek, ' Feinere Bau d. 

 Nervensystems,' p. 19) that the coloration is not due to a 

 visible precipitate, but is a true stain, accompanied (in 

 unsuccessful impregnations) by a precipitate which does not 

 help the stain but is injurious to it. It has been maintained 

 that the stain is merely superficial, and the method has been 

 called an " incrustation method." I find that it extends 

 throughout the whole thickness of the impregnated elements. 



1''he chemical nature of the stain has not been made out. 



A critical review of the Golgi metliod by Weigebt may be found in 

 Ergebnisse der Anatomie, v, 1895 (1896), p. 7. 



See also Hill {Brain, part 73, 1896, p. ]), Azoulay {Coinptes Beud. 



