410 CENTRAL NERVOUS SYSTEM. 



It is then removed into glycerin (either pure or with 1 per cent, of carbolic 

 acid). It floats at first, but gradually sinks as the alcohol evaporates. As 

 soon as it has sunk just below the surface it may be removed and exposed 

 to the air. 



It is set aside to " evaporate " in a convenient place for a few days. As 

 soon as the surface has become dry, it is varnished with india rubber or 

 (better) with marine glue varnish diluted with a little alcohol. This com- 

 pletes the process. 



If it be desired to make dissected preparations, the necessary dissection 

 should be made on removing the encephalon from the alcohol before putting 

 into glycerin. 



Bichromate of potash may be used for hardening in solutions gradually 

 increasing in concentration from 2 to 4 per cent. The liquid must be fre- 

 quently changed ; the immersion must be of not less than a month's duration. 

 Six to eight days will suffice for the alcohol-bath, or this may be altogether 

 omitted. 



Nitric acid is used in solutions of from 10 to 12 per cent, for twelve to 

 fifteen days. (Encephala float in this liquid, and must therefore be fre- 

 quently turned over. It is this reagent that gives the toughest prepara- 

 tions.) 



Concerning the value of the process, Golgi (from whose abstract I take 

 the foregoing account) states that after a series of experiments he is able to 

 affirm that for preservation of the volume, the colour, the finer relations of 

 the parts, and the physiognomy proper to the organ, the process is far 

 superior to any hitherto known. I am able to add that I saw specimens of 

 Giacomini's preparations at the Milan International Exhibition of 1881, 

 and think it would be hard to over-praise their beauty of aspect. 



It should be added that histological detail is preserved to a remarkable 

 extent by this process, and that excellent sections may be cut at any time 

 from the hardened brains. And as the preparations take up as little room 

 as possible, there seems no reason why the process should not be generally 

 adopted in medical schools, lunatic asylums, and similar institutions. 



The method may also be applied, with most perfect success, to the pre- 

 servation of small animals entire, such as Batrachia, K-eptilia. It is well to 

 inject them with the zinc solution. 



Another " dry " method has been given by MAX FLESCH (Mt. Naturf. 

 Ges. Bern , 1887, p. xiii). He hardens in alcohol, and then brings the 

 brains through Calberla's mixture ( 405) into glycerin containing (1 part 

 to 3000 of) sublimate. He does not appear to varnish his preparations. 

 See Journ. Roy. Mic. Soc., 1888, p. 507. 



781. Dissociation Methods. Maceration of nervous tissue is a method 

 that rendered service years ago for the isolation of ganglion-cells with their 

 processes, &c. These details can, however, now be studied in situ by means 

 of the excellent methods of special staining or impregnation that have been 

 given in the foregoing pages, so that the maceration methods can hardly 

 claim now to be useful for purposes of research, and may at most claim to 

 serve as means of demonstrating to beginners the general characters of 

 ganglion-cell processes. See, however, the following : 



