. ALCOHOL. 41 



you take " 8 vols. of pure hydrochloric acid of 25 per cent. HC1." Mayer 

 now dissolves the picric acid in the hydrochloric acid water, so that the for- 

 mula runs : 



Water 100 vols. 



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

 Picric acid, as much as will dissolve. 

 The fluid is used undiluted. 

 The properties of this fluid are similar to those of picro-nitrie acid. 



59 a. Picro-chromic Acid. See ante, 41. 



60. Picro-chromo-sulphuric Acid (KEISEE, Biblioth. Zool., H. vii, 1 

 Halfte, 1891; Zeit.f. wiss. MiJc., viii, 3, 1891, p. 363). Keiser found the 

 following mixture excellent for Acanthocephali : 



Picric acid ....... 1 gramme. 



Cone, sulphuric acid 10 grammes. 



Chromic acid ...... 1 gramme. 



Water ....... 1000 grammes. 



To be warmed to 55 C., allowed to act for 15 to 20 minutes, washed out 

 for 5 to 10 minutes with hot water, and afterwards for some days in 60 per 

 cent, alcohol. 



61. 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, 34 and 35). The results are identical 

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

 difficult. 



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

 Journ. Eoy. Hie. Soc., 1891, p. 418). Alcobol (95 per cent.), 250 parts ; 

 water, 250 parts ; picric acid, 1 part. Fix for about 24 hours, wash out for 

 a day in alcohol of 67 to 70 per cent., and then for a day or longer in 

 alcohol of 75 to 82 per cent. 



Other Fixing Agents. 



63. Alcohol. For fixing, only two grades of alcohol are 

 found generally useful very weak alcohol on the one hand, 

 and absolute alcohol on the other hand. Absolute alcohol 

 ranks as a fixing agent because it kills and hardens with such 

 rapidity that structures have not time to get deformed in the 

 process by the energetic dehydration that unavoidably takes 

 place. Dilute alcohol ranks as a fixing agent in virtue of 

 being of such a strength as to possess a sufficiently energetic 

 coagulating action and yet contain enough water to have but 

 a feeble and innocuous 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 (such as cor- 



