('IIAFTEK V. 



Tissues iixed in picric acid can be perfectly stained in 

 any stain. It is seldom necessary to remove the picric acid 

 by \\a-liiiiLr 'iit before staining. Paracarmine, Borax- 

 carniini', >r Ila-inacalcium may be recommended for entire 

 objects. 



Tin- m<>st important property of picric acid is its great 

 ]M-iK'trati<>n. This renders it peculiarly suitable for the 



parution of chitinous structures. 



94. Picric Alcohol (GAGE, Proc. Amer. Soc. Micr., 1890, p. 120).- 

 Alc. .lid /!'"> per cent.). 250 parts ; water, 250 parts; picric acid, 1 part. 



95. Picro-acetic Acid. BOVERI (Zellenstudien, 1, 1887, p. 11) dilutes 

 a < 'iic.-ut rated aqueous solution of picric acid with two volumes of water 

 and adds 1 per cent, of acetic acid. According to my experience, the 

 r- --nits are miserable. 



ZIMMER'S mixture (from DEEGENER, Zool. Jahrb. Abth. Morph., xxvii, 

 1!M>, p. (i:M). Saturated aqueous solution of picric acid, 10 parts; abso- 

 lute alcohol, 9; acetic acid, 1. 



96. Picro-sulphuric Acid (KLEINENBERG, Quart. Journ. Mic. Sci., 

 April. 1879. p. 208; MAYER, Mitt. Zool, Slat. Neapel, ii, 1880, p. 2).- 

 MAYER takes distilled water, 100 vols. ; sulphuric acid, 2 vols. ; picric 

 acid, as much as will dissolve. 



Liquid of KLEINENBERG is made by diluting the concentrated picro- 

 snlphuric acid prepared as above with three times its volume of water. 



I hold that the concentrated solution is generally preferable. This 

 particularly applies to marine organisms. 



Wash out with successive alcohols, beginning with 70 per cent., never 

 with water. 



}\'t<rm alcohol extracts the acid much more quickly than cold, without 

 which u-celes may be required to fully remove the acid from chitinous 

 structures. 



This liquid may still be useful for Arthropoda, on account of its great 

 power of penetrating ehitin ; and for some embryological purposes. 

 For a fuller account see early editions. 



97. Picro nitric acid (MAYER. Mittli. Zool. Stat. Neapel 1881 

 P- ft).- 



W^ter . 100 vols. 



Nitric acid (of 25 per cent, N 2 6 ) . . 5 

 Picric acid, as much as will dissolve. 



I'n.j.'-rti.'s of this fluid similar to those of picro-sulphuric acid, with 



the advantage of avoiding the formation of gypsum crystals, and the 



disadvantage that it is much more difficult to soak out of the tissues. 



lav. -r states that with eggs containing a large amount of yolk material, 



of I'almurus, it gives Letter results than nitric, picric, or 



