868 SUMMARY OF CURRENT RESEARCHES RELATING TO 



from the acid to the alcohol, it is advisable to take them up by means 

 of a pipette or spatula, so that a few drops of the acid may be trans- 

 ferred along with them. The objects, sinking quickly to the bottom, 

 remain thus for a short time in the medium with which they are 

 saturated, and are not brought so suddenly into contact with the 

 alcohol. In a few minutes the diffusion is finished ; and they may 

 then be placed in a fresh quantity of alcohol, which must be shaken 

 up frequently and renewed from time to time until the acid has been 

 entirely removed. 



The sulphuric acid contained in this fluid causes connective tissue 

 to swell, and this fact should be borne in mind in its use with verte- 

 brates. To avoid this difficulty Kleinenberg has recommended the 

 addition of a few drops of creosote, made from beech-wood tar, to 

 the acid. According to Dr. Mayer's experience, however, the 

 addition of creosote makes no perceptible difference in the action of 

 the fluid. 



Professor Emery finds the process very useful for embryos of 

 vertebrates and for fishes, but they should not be allowed to remain 

 in the acid more than three or four hours. Although the method is 

 considerably the best for preserving Crustacea as a rule, it will not 

 do for the parasitic species, in which it produces swellings, dissolu- 

 tion of parts of the tissues, &c. 



2. Picro-nitric or Picro-hydrochloric acid. — Kleinenberg's fluid 

 must not be used with objects (e. g. Echinoderms) possessing cal- 

 careous parts which it is desired to preserve, for it dissolves carbonate 

 of lime and throws it down as crystals of gypsum in the tissues. For 

 such objects picro-hydrochloric or picro-nitric acid may be used, 

 prepared as follows : — 



Water 100 volumes. 



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



[or hydrochloric acid (25 per cent. HC1) 8 „ ] 

 Picric acid as much as will dissolve.* 



Picro-nitric acid also dissolves carbonate of lime, but it holds it 

 in solution, and thus the formation of crystals of gypsum is avoided. 

 In the presence of much carbonate of lime, the rapid production of 

 carbonic acid is liable to result in mechanical injury of the tissues, 

 hence in many cases chromic acid is preferable to picro-nitric 

 acid. 



Picro-nitric acid is, in most respects, an excellent preservative 

 medium, and as a rule will be found to be a good alternative in 

 those cases where picro-sulphuric acid fails to give satisfactory 

 results. Dr. Mayer commends it very strongly, and 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. It is not so readily removed from objects as picro-sulphuric 

 acid, and for this reason the latter acid would be used wherever it 

 gives equally good preparations. 



* This mixture is uted undiluted. 



