

ALUM. 29 



44. Bichromate and Cupric Sulphate 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 cc. 



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. 



The rationale of this mixture is, that it fixes tissues faithfully, 

 without causing the production of the delusive reticular pre- 

 cipitates of albuminoids which we have mentioned as being 

 produced by chromic acid that is the part played by the 

 bichromate and sulphate ; and that it also fixes faithfully the 

 chromatin of nuclei that is the part played by the "organic 

 acid. 



44 a. Cupric Sulphate. Cupric sulphate was recommended 

 some few years ago in one of the well-known handbooks. It 

 was recommended (in a place which I cannot now find) to be 

 used for marine organisms in saturated solution in sea-water, 

 the organisms to be preserved in the solution itself till wanted. 

 It has been quite recently ( Arch. d. Sci. phys. et. nat., Juin, 

 1889, t. xxi, p. 556) recommended by BEDOT for the prepara- 

 tion of Siphonophora and other delicate pelagic animals. 

 Bedot directs that a large quantity of 15 to 20 per cent, 

 solution of the salt be suddenly added to the sea-water con- 

 taining the animals. As soon as the animals are fixed (which 

 happens in a few minutes), a few drops of nitric acid are to be 

 added and mixed in (this is in order to prevent the formation 

 of precipitates), and the whole is left for four to five hours. 

 The animals are then to be hardened before bringing them into 

 alcohol. Bedot recommends that this be done in a large 

 quantity of Flemming's strong solution ( 36), in which the 

 animals should remain for twenty-four hours at least. 



This promises to be a valuable method. Bedot has been 

 able by this means to preserve Forskalia and Halistemma, 

 which are amongst the most difficult forms known to me. 



44 b. Alum. Alum has been used for fixing purposes, and may therefore 



