56 FIXING AND HARDENING AGENTS. 



98. Picro-hydrochloric Acid (MAYER, ibid.). 



Water 100 vols. 



Hydrochloric acid (of 25 per cent. HC1) . 8 ,, 

 Picric acid, as much as will dissolve. 



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



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

 1 per cent, chromic acid solution . . 25 ,, 



Water 65 



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

 quoted as " liquid of Haensel." 



Lo BIANCO takes equal parts of picro- sulphuric acid and chromic acid 

 of 1 per cent. 



KAWITZ (Leitfaden, 1895, p. 24) takes 1 part of picro-nitric acid, 

 and 4 parts 1 per cent, chromic acid. Wash out in 70 per cent, 

 alcohol. 



100. 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 ( 42), and finds the results identical, 

 so far as regards the fixation of nuclei. The fixation of cytoplasm is in 

 my preparations decidedly inferior. 



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. 



EAWITZ (Leitfaden, p. 24) takes picro-nitric acid, 6 vols. ; 2 per cent, 

 osmic acid, 1 vol. Fix for half to three hours. Transfer direct to 70 per 

 cent, alcohol. 



101. Piero-platinie and Picro-platin-osmic Mixtures. 0. VOM RATH 

 (loo. cit., last , pp. 282, 285) makes a picro -platinic mixture with 

 200 c.c. saturated aqueous solution of picric acid, 1 grm . 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. 



Other PICRIC MIXTURES. See 70 and 110 to 112. 



Other Fixing and Hardening Agents. 



102. Alcohol. For fixing only two grades of alcohol should be 

 employed very weak, or absolute. Absolute alcohol ranks as a 

 fixing agent because it kills and hardens with such rapidity that 

 structures have hardly time to get deformed in the process ; very 

 weak, because it possesses a sufficiently energetic coagulating action 

 and yet contains enough water to have but a feeble dehydrating 

 action. The intermediate grades do not realise these conditions, 

 and therefore should not be employed alone for fixing. But they 

 may be very useful in combination with other fixing agents by 



