ZOOLOGICAL STATION IN NAPLES. 10^ 



95 volumes 70 per cent, or 90 per cent, alcohol. 

 3 ,, hydrochloric acid,* 

 for larger objects, particularly if they are designed for preservation 

 in museums. The fluid should be frequently shaken up, and the 

 object only allowed to remain until thoroughly saturated, then 

 transferred to pure 70 per cent, or 90 per cent, alcohol, which 

 should be changed a few times in order to remove all traces of the 

 acid. For small and tender objects, acid alcohol, although pre- 

 ferable to pure alcohol, gives less satisfactory results than picro- 

 sulphuric acid. 



4. Boiling Alcohol. — In some cases among the Arthropods, 

 Dr. Mayer has found it difficult to kill immediately by any of the 

 ordinary means, and for such cases recommends boiling absolute 

 alcohol, which kills instantly. For Tracheata this is often the only 

 means by which the dermal tissues can be well preserved, as cold 

 alcohol penetrates too slowly. 



5. Osmic Acid. — Dr. Mayer employs osmic acid as a staining- 

 medium for the hairs, bristles, etc., of the dermal skeleton of 

 Arthropods. The lustre of Sapphirina is preserved by this acid,t 

 and according to Emery, the colour of the red and the yellow 

 fatty pigments of fishes. 



Van Beneden found osmic acid the best preservative fluid for 

 the Dicyejuidce, and my experience leads to the same conclusion.;!: 



Although Dr. Mayer seldom uses this medium where histolo- 

 gical details are required, he observes that in those classes of 

 animals whose bodies are easily penetrated with watery fluids, osmic 

 acid is seldom to be dispensed with. 



Bleaching. — It often happens that objects treated with osmic 

 acid continue to blacken, after removal from the acid, until they 

 are entirely worthless, and such results are even more annoying 

 than the difficulties in the way of staining. It has been said that 



• Acid alcohol as above prepared loses its original qualities after standing some 

 time, as ether compounds are gradually formed at the expense of the acid. 



f See corrosive sublimate, p. 107. 



X One of the best objects for testing methods is found in Phronima sedentana. 

 Here the cells and nuclei are so sharply defined that they can be seen in the living 

 animal, and so the effect of a preservative fluid can be easily studied. 



