ZOOLOGICAL STATION IN NAPLES. 99 



the same fluid often does the work of killing and hardening, and 

 sometimes of preserving too, it is impossible to divide them into 

 three classes corresponding to the kinds of work, except by 

 repeating many of them twice, and some of them three times. 

 While it is therefore more convenient to include them all under 

 *' preservative fluids," as Dr. Mayer has done, it is none the less 

 important to remember what kind or kinds of work each fluid is 

 expected to accomplish. 



Kleinenberg'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. 



I. Kleinenberg's Fluid.* 



Picric acid (saturated solution in distilled water) i oo volumes. 

 Sulphuric acid (concentrated) ... ... 2 „ 



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

 finally add as much creosote % as will mix. 

 Dr. Mayer prepares the fluid as follows : — 



Water (distilled) ... ... ... 100 volumes. 



Sulphuric acid ... ... ... 2 „ 



Picric acid (as much as will dissolve). 

 Filter and dilute as above. No creosote is used. 



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

 are then, in order to harden and remove the acid, transferred to 

 70 per cent, alcohol, where they may remain 5 — 6 hours. They 

 are next placed in 90 per cent, alcohol, which must be changed at 

 intervals until the yellow tint has wholly disappeared. 



Simwiary of Dr. Mayer^s remarks o?t Kleiiienher^s Fluid. — The 

 advantage of this fluid is, 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 

 // 7nay 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 unfavourable to staining. Picro-sulphuric acid does 



* Quart. Journ. Micro. Sci., Vol. XIX., pp. 208—9, 1879. 



t Dr. Mayer uses the fluid undiluted for Arthropoda. 



X Creosote made from beechwood tar. 



