52 CHAFTBK IV. 



solution. A spinal cord may be hardened in it in four days 

 at the temperature of an incubator, and in ten days at the 

 normal temperature (FoL, Lehrb. d. vergl. mik. Anat., p. 106). 

 I believe it to be one of the best hardening agents known for 

 voluminous objects. Human embryos of several months may 

 be conveniently hardened in it. 



Nerve-centres that have been hardened in Erlicki's fluid frequently con- 

 tain dark spots with irregular prolongations, simulating ganglion-cells. 

 These were at one time taken to be pathological formations, but they are 

 now known to consist of precipitates formed by the action of the hardening 

 fluid. They may be removed by washing with hot water, or with water 

 slightly acidified with hydrochloric acid, or by treating the specimens with 

 0'5 per cent, chromic acid before putting them into alcohol (TscniscH, 

 Virchow's Arch., Bd. xcvii, p. 173 : EDINGEB, Zeit.f. wiss. Mik., ii, 2, p. 245 ; 

 LOEWENTHAL, Rev. med. de la Suisse romande, 6me annee, i, p. 20). 



59. Bichromate and Oupric Sulphate or Sublimate Mixture 

 (KULTSCHITZKY, Zeit. f. wiss. Mik., iv, 3, 1887, p. 348). A saturated 

 solution of bichromate of potash and sulphate of copper in 50 per cent, 

 alcohol, to which is added at the instant of using a little acetic acid, five or 

 six drops per 100 c.c. 



To make the solution, add the finely powdered salts to the alcohol in 

 excess, and leave them together in total darkness, for twenty-four hours. 



Fix for twelve to twenty-four hours in the dark, otherwise the salts will 

 be precipitated. Then treat with strong alcohol for twelve to twenty-four 

 hours, and make sections. 



More recently (Arch.f. mik. Anat., xlix, 1897, p. 8), KULTSCHITZKY re- 

 commends a mixture of two parts bichromate, part corrosive sublimate, 

 50 parts 2 per cent, acetic acid, and 50 parts 96 per cent, alcohol. As 

 part of the bichromate precipitates, the mixture should be filtered after 

 twenty-four hours. Tissues of vertebrates may remain in it for four to six 

 days. 



60. Bichromate of Ammonia. A review of the literature of the sub- 

 ject shows that this salt is in considerable favour for hardening, for what 

 precise motive is not apparent. Its action is very similar to that of the 

 potassium salt. Fol says that it penetrates somewhat more rapidly, and 

 hardens somewhat more slowly. It should be employed in somewhat 

 stronger solutions, up to 5 per cent. 



61. Neutral Chromate of Ammonia is preferred by some anatomists. 

 It is used in the same strength as the bichromate. Klein has recommended 

 it for intestine, which it hardens, in 5 per cent, solution, in twenty-four 

 hours. 



62. Bichromates and Alcohol. Mixtures of either bichromate of 

 potash or of ammonia with alcohol may be employed, and have a more rapid 

 action than the aqueous solution. Thus HAMILTON takes for hardening 



