NEUROLOGICAL METHODS. 425 



changed every day, and later on as often as it becomes 

 yellow. At the end of the reaction the preparations will be 

 found decolourised, and offering- the aspect of fresh tissue. 

 They may be left in the bichloride for any time. 



In Rendiconti R. 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. 



The reaction may be said to have begun by the time the 

 tissues are nearly dec-olourised. From that time onwards 

 sections may be made day by day and examined, and those 

 which it is desired to preserve may be mounted. 



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-toniiig 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. 



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

 " apparently black reaction," the tissues appearing black by 

 transmitted light, irhiteby reflected light. GOI.GI 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 rami- 

 fications of the processes. These are made more evident than 

 by any other process except the bichromate and silver-nitrate 

 process. (2) Nuclei, which is not the case with the silver 

 process. (3) 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. 

 (4) The blood-vessels, and particularly their muscular 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 



