904 SUMMARY OF CURRENT RESEARCHES RELATING TO 



PercUoride of Mercury in the study of tlie Central Nervous 



System.* — Golgi's methods for staining nerve-elements black are 

 based on the action of nitrate of silver and perchloride of mercury 

 following the use of bichromate of potash. The mercurial salt, how- 

 ever, does not give a real black colour, but renders the elements 

 opaque and causes them to appear black under the Microscope. For 

 small pieces the method is to immerse in a 2 per cent, solution of 

 bichromate or in Miiller's fluid for a month. They are then trans- 

 ferred to a 0*5 per cent, solution of perchloride, which is daily 

 renewed until all colour traces of bichromate have disappeared. 



Dr. C. Mondino applies the foregoing method to whole brains by 

 injecting through a carotid (the other and the vertebrals being tied) 

 Miiller's fluid by the pressure-bottle process. The excess fluid passes 

 out by the jugular veins, and when the stream has become very slow 

 or stopped, the brain may be transferred to Miiller's fluid, where it 

 should remain for a couple of months, though a longer period is not 

 harmful. The carotid injection process is not absolutely necessary, as 

 the brain after removal from the body may be placed in Miiller's fluid 

 at once. In this case the membranes must be stripped off. Directly 

 after removal from the fluid, the brain must be placed in a 1/2 per 

 cent, aqueous solution of perchloride and this must be continually 

 changed so long as the solution is stained by the bichromate. It is 

 proper to leave the brain in the perchloride solution for at least two 

 or three weeks after all trace of bichromate has disappeared. 



Sections are best made by Gudden's microtome. It is unnecessary 

 to soak these brains in paraffin ; owing to their consistence, imbedding 

 alone is found to be sufficient. Out of a whole brain not more than 

 twenty sections will be lost. 



While by other methods thin sections are a sine qua non for 

 observation, in this, thick slices are almost necessary, the chief 

 advantage of which is obviously that any fibre can be followed 

 throughout its course in the brain. When a section has been made 

 it is placed at once on a slide and then washed with water to remove 

 any bits of paraffin. It is then dried with blotting-paper. Next a 

 little pure creosote is placed on the centre of the section, which is 

 thereby rendered quite transparent in a few hours. After draining 

 away the excess of creosote, the specimen is covered with dammar. 

 No cover-glass is used. 



The author claims the following advantages for this method. It 

 is the only one which shows the course of nerve-fibres throughout 

 the brain. It is extremely simple. In all other methods, the speci- 

 mens must be thin, require to be stained after section, and to go 

 through many processes ; all this renders them liable to injury. It 

 is inexpensive, as the reagents used are very cheap when compared 

 with those required for other methods. 



Macroscopically, in other methods there is diminution of volume, 

 disappearance of difference between white and grey matter, while 

 brains prepared in perchloride show the difference between the white 



* Zeitschr. f. Wiss. Mikr., it. (1885) pp. 157-63. 



