METHODS FOB GENERAL STAINS. 831 



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 Grolgi 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. 



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. Mount in balsam or glycerin ; the 

 latter seems the better preservative medium. 



The result of this process is not a true stain, but an " appa- 

 rently black reaction ;" the tissues appearing black by trans- 

 mitted light, white by reflected light. Golgi thinks that 

 there is formed in the tissue elements a precipitate of some 

 substance that renders them opaque. The elements acted on 

 are (1) the ganglion-cells, with all their processes and ramifi- 

 cations of the processes. These are made more evident than 

 by any other process except the bichromate and silver-nitrate 

 process. An advantage of the mercury process is that it 

 demonstrates nuclei, which is not the case with the silver 

 process. (2) Connective-tissue corpuscles in their charac- 

 teristic radiate form. But the reaction in this case is far 

 less precise and complete than that obtained by the silver 

 process. (3) The blood-vessels, and particularly their mus- 

 cular-fibre cells. 



The method gives good results only with the cortex of the 

 cerebral convolutions, hardly any results at all with the 

 spinal cord, and very scanty results with the cerebellum. 

 And, on the whole, the method shows nothing .more than can 



