68 CHAPTER V. 



p. 867). By picro-sulphuric acid, without any qualifying term, I under- 

 stand a fluid made (following Mayer, loc. cit.) as follows : Distilled water, 

 100 vols. ; sulphuric acid, 2 vols. ; picric acid, as much as will dissolve 

 (this will be about 0'25 per cent., as the picric acid is much less soluble in 

 sulphuric acid solution than in water). This may also, in any case in 

 which confusion is likely to arise, be called "concentrated" or "undiluted 

 picro-sulphuric acid." 



By " liquid of Kleinenberg " I understand a mixture suggested by 

 Kleinenberg (loc. cit.), and best made by diluting the concentrated picro- 

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



Of these two formulis the one formerly most employed is that given by 

 Kleinenberg the dilute mixture ; undiluted picro-sulphuric acid being 

 reserved for objects requiring special treatment, chiefly Arthropods. I 

 hold that Kleinenberg's solution is much weaker than is desirable in the 

 majority of cases, and should be reserved for special cases, such, perhaps, as 

 that for which it was originally proposed, the embryology of the earth- 

 worm ; the concentrated solution being generally preferable. This particu- 

 larly applies to marine organisms. 



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

 with water. 



Warm alcohol extracts the acid much more quickly than cold, without 

 which weeks may be required to fully remove the acid from chitinous 

 structures. 



This liquid, once the classical fixative, is now almost entirely abandoned, 

 I think rightly, as its fixing qualities are at the best only second-rate. 

 For Arthropoda it may still be useful, on account of its great power of 

 penetrating chitin. For a fuller account see previous editions. 



91. Picro-nitric Acid (MAYER, Mitth. Zool. Stat.'Neapel, 1881, p. 5 ; 

 Journ. Roy. Mic. Soc. (N.S.), ii, 1882, p. 868). 



Water 100 vols. 



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



Picric acid, as much as will dissolve. 



The properties of this fluid are very 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. 

 The process of .Telinek, 89, may be useful here. Mayer states that with 

 eggs containing a large amount of yolk material, like those of Palinurus, 

 it gives better results than nitric, picric, or picro-sulphuric acid. I myself 

 consider it distinctly superior to picro-sulphuric. 



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



Water 100 vols. 



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

 Picric acid, as much as will dissolve. 



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



