ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 867 



kind or kinds of work cacli fluid is expected to accomplish. Kleinen- 

 berg's picro-sulphuric acid, for instance, now so much used in the 

 Naples Aquarium, is not a hardening fluid. It serves for killing, 

 and thus prepares for subsequent hardening. 

 1. Kleineriberg' 8 Picro-sulphuric acid*: — 



Ticric acid (cold saturated solution in 



distilled water) , .. .. 100 volumes 



Sulphuric acid (concentrated) .. .. 2 ,, 



Filter the mixture, and dilute it with three times its bulk of water 

 (or for Arthropoda undiluted), finally add as much creosote (made 

 from beech-wood tar) as will mix.f 



Objects are left in the fluid three, four, or more hours ; J and are 

 then, in order to harden and remove the acid, transferred to 70 per 

 cent, alcohol, where they may remain 5 to 6 hours. They are next placed 

 in 90 per cent, alcohol, which must be changed at intervals until the 

 yellow tint has wholly disappeared. 



The advantages of this fluid are, that it kills quickly, by taking 

 the place of the water of the tissues ; that it frees the object from sea- 

 water and the salts contained in it, and that having done its work it 

 may be wholly replaced by alcohol. In this latter fact lies the superiority 

 of the fluid over osmic and chromic solutions, all of which produce 

 inorganic precipitates and thus leave the tissues in a condition un- 

 favourable to staining. Picro-sulphuric acid does not, like chromic 

 solutions, harden the object, but simply kills the cells. 



As this fluid penetrates thick chitine with difficulty, it is necessary, 

 in order to obtain good preparations of larger Isopoda, insects, &c, to 

 cut open the body with the scissors and fill the body-cavity with the 

 liquid by means of a pipette. In larger objects care should be taken to 

 loosen the internal organs so that the fluid may find easy access to 

 all parts. 



The fluid should be applied as soon as the body is opened, so that 

 the blood may not have time to coagulate and thus bind the organs 

 together. A large quantity of the fluid should be used (especially 

 when objects with large internal cavities have to be prepared whole), 

 and it must be changed as often as it becomes turbid. The same rule 

 holds good in the use of all preservative fluids. It is well also, 

 especially with larger objects, to give the fluid an occasional stir- 

 ring up. 



In order to avoid shrinkage in removing small and tender objects 



* Quart. Journ. Micr. Sci., xix. (1879) pp. 208-9. See this Journal, ii. (1879) 

 p. 461. 



t Dr. Mayer prepares the fluid as follows : — Water (distilled), 100 vols. ; 

 sulphuric acid, 2 vols. ; picric acid as much as will dissolve. Filter and dilute 

 as above. No creosote is used. 



X Dr. Mayer's own remarks are : — How long objects should remain in the 

 acid depends of course upon their nature. Usually a few hours is sufficient, but 

 for larger objects and those containing a large percentage of water a longer time 

 is necessary. In some cases a whole day does not produce any injurious effect. 



