432 CHAPTER XXXIV. 



even entire hemispheres. In this case the brain should at 

 first be treated by repeated injections of the liquid. Fifteen 

 to twenty days' immersion will suffice, or even six to eight, 

 but twenty to thirty should be preferred, and an immersion 

 of several months is not injurious. 



The tissues when hardened are passed direct from the 

 bichromate into 0'5 per cent, solution of bichloride of mercury. 

 An immersion of eight to ten days therein is necessary in 

 order to obtain a complete reaction (or for entire hemispheres 

 two months or more). The solution must at first be 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. 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, 

 sublimate 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 decolourised. From that time onwards 

 sections may be made day by day and mounted if successful. 



Before mounting, the sections must be repeatedly washed 

 with water, 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 (prefer- 

 ably) glycerin. 



The elements acted on are (1) The ganglion cells, with 

 all their processes and ramifications. (2) Nuclei, which is 

 not the case with the silver process. (3) Neuroglia cells. 

 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 is said to give good results only with the 

 cortex of the cerebral convolutions, hardly any results at all 

 with the spinal cord, and very scanty results with tho cere- 



