FIXING AND HARDENING AGENTS. 69 



93 Picro-chromic Acid (FoL, Lehrb., p. 100). 



Picric acid, sol. sat. in water . . . .10 vols. 

 1 per cent, chromic acid solution . . 25 



Water 65 



At the instant of using you may add O'OOo of osmic acid, which makes 

 the action more energetic. 



I have seen Fol's formula, with the addition of a trace of acetic acid, 

 quoted as " liquid of Haensel " I know not with what justification. 



94. Picro-nitro-chromic Acid (RAWITZ, Leitfadtn f. liistol. Unter- 

 suchungen, 1895, p. 24). One part of picro-nitric acid, and four parts 



1 per cent, chromic acid. Wash out in 70 per cent, alcohol. 



95. Picro-osmic Acid. FLEMMING (Zells. Kern u. Zelltli., p. 381) has 

 experimented with mixtures made by substituting picric for chromic acid in 

 the chromo-osmic mixtures (ante, 46 and 4,7). The results, he says, are 

 identical so far as regards the fixation (of nuclei) ; but staining is rendered 

 more difficult. 



0. VOM RATH (Anat. Anz , xi, 1895, p. 289) adds to 200 c.c. of saturated 

 aqueous solution of picric acid, 12 c.c. of 2 per cent, solution of osmic acid, 

 and 2 c.c. of glacial acetic acid. 



Flemming may be right as regards the nuclei ; but the fixation of cyto- 

 plasm is in my preparations decidedly inferior. 



96. Picro-nitro-osmic Acid (RAWITZ, Leitfaden, p. 24). Picro- 

 nitric acid, 6 vols. ; 2 per cent, osmic acid., 1 vol. Fix for to 3 hours. 



nsfer direct to 70 per cent, alcohol. The mixture keeps well. 



' 97. Picro-platinic and Picro-platin-osmic Mixtures. 0. TOM 

 RATH (Zoc. cit., pp. 282, 285) makes a picro-platinic mixture with 200 c.c. 

 saturated aqueous solution of picric acid, 1 g. of platinic chloride (dissolved 

 in 10 c.c. of water), and 2 c.c. of glacial acetic acid. 



The picro-platin-osmic mixture, which is, in my opinion, 

 much superior, is made by adding to the foregoing 25 c.c. of 



2 per cent, osmic acid. 



98. Picric Alcohol (GAGE, Proc. Amer. Soc. Micr., 1890, p. 120; 

 Jonrn. Roy. Mic. Soc., 1891, p. 418). Alcohol (95 per cent.), 250 parts; 

 water, 250 parts; picric acid, 1 part. 



Other Fixing and Hardening Agents. 



99. Alcohol. For fixing it is generally held that only two 

 grades of alcohol should be employed very weak alcohol on 

 the one hand, and absolute alcohol on the other hand. 



