GENE HAL STAINS. 399 



per le Scienze Nediche, 1878, p. 3). This method, which may 

 be said to be in principle identical with the bichromate of 

 potash and silver nitrate method of the author, consists, like 

 the latter, of two processes : 1, hardening in bichromate ; 2, 

 treatment with bichloride of mercury. 



For hardening, use either a solution progressively raised 

 in concentration from 1 per cent, to 2 4 per cent., or Mutters 

 solution. Take small pieces of tissue (not more than 1 to 2 

 c.c.), large quantities of liquid, and change the latter fre- 

 quently, so as to have it always clear. Fifteen to twenty 

 days' immersion will suffice, but twenty to thirty should be 

 preferred. 



The tissues are then passed direct from the bichromate 

 into the bichloride of mercury. The solutions of the latter 

 employed by Golgi varied from 0*25 per cent, to 0*50 per 

 cent. : he cannot say which strength is to be preferred. The 

 immersion in the bichloride must be much longer than the 

 immersion in the nitrate of silver bath of that process : for 

 the latter, twenty-four to forty-eight hours suffice ; but in the 

 bichloride an immersion of eight to ten days is necessary in 

 order to obtain a complete reaction through the whole thick- 

 ness of the tissues. During the bath the bichromate will 

 diffuse out from the tissues into the bichloride, which must 

 be changed every day ; at the end of the reaction the pre- 

 parations will be found decolourised, and offering the aspect 

 of fresh tissue. They may be left in the bichloride for any 

 time. 



In Bendiconti B. 1st. Lombardo di Sci. Milano, 2, xxiv, 1891, pp. 594, 

 656 (see Zeit. f. wiss. Mik., viii, 3, 1891, p. 388) Golgi says that for the 

 study of the diffuse nervous reticulum of the central nervous system the 

 best results are obtained by keeping the preparations in 1 per cent, sub- 

 limate for a very long time, two years being not too much in some cases. 



Before mounting, the sections that have been cut must be 

 repeatedly washed with water (if it be wished to mount them 

 permanently), otherwise they will be spoilt by the formation 

 of a black precipitate. In the last place quoted Golgi says 

 that after washing they may be toned by putting them for a 

 few minutes into a photographic fixing-and-toning bath, after 

 which it is well to wash them again, and stain them with 

 some acid carmine solution. Mount in balsam or glycerin ; 

 the latter seems the better preservative medium. 



