AND HOW TO USE IT. 181 



these latter many details suffer, especially the bacillary layer of 

 the retina. The objects for examination are placed fresh in the 

 fluid, and kept there from twenty-four to thirty-six hours. There 

 is no need to keep them in the dark, as the osmic acid, in con- 

 junction with chromic acid, does not undergo such rapid changes 

 by light as when alone. In the case of cochlea, young bones, 

 etc., a further treatment with 0*25 per cent, to 0*5 per cent, of 

 chromic acid may be necessary for complete decalcification. The 

 object is then washed and placed in spirit, and the sections, when 

 cut, may either be examined in glycerine, or treated successively 

 with alcohol and turpentine, and then mounted in Canada Balsam. 

 The great advantages of this fluid are its rapid hardening proper- 

 ties^ and the fact that no further staining is necessary, the osmic 

 acid giving sufficient colour to the cells even when mounted in 

 balsam. 



Muller's Fluid takes a longer time to prepare than chromic 

 acid. It is made as follows : — Bichromate of Potass., 2 parts ; 

 sulphate of soda, i part; water, 100 parts. The ingredients 

 should be pounded in a mortar, and then warm water added 

 until they are dissolved. The advantages of this mixture are, 

 first, that larger pieces can be hardened in it ; second, it does not 

 require changing after the first week or two, but it will take from 

 five to seven weeks to harden anything, according to its size. 

 When sufficiently hardened, wash well and place in dilute spirit, 

 as recommended for the chromic acid mixture. 



Muller's Fluid, a Variation of (sometimes called Ehrlich's 

 hardening solution). — Take bichromate of potash^ 2 to 2 J parts ; 

 sulphate of copper (J per cent, solution) i part (instead of 

 sulphate of soda) ; and water, 100 parts. The hardening proper- 

 ties are far superior to those of Muller's fluid. 



Muller's Fluid and Spirit.— Three parts of Muller's fluid and 

 I part of methylated spirit. It is good for nerve tissues, muscle, 

 and retina. This must be kept in a dark place to prevent the 

 chromium salts from separating. 



Methylated Spirit. — Many tissues can be hardened in spirit 

 alone if they are placed in dilute spirit at first, so that the ele- 

 VOL. v. o 



