164 



The Naturalist. 



it must he remembered that the liquid after some time loses its 

 properties and at the expense of the hjdrochloxic acid, builds up 

 ether compounds. 



Boiling Alcohol. — In some cases amongst the Arthropoda it is 

 almost impossible, with the ordinary methods in use, to kill as quickly 

 as necessary. In these cases Dr. Mayer has used boiling absolute 

 alcohol which kills instantly, as for instance in the Tracheata. 



Osmic Acid. — Dr. Mayer's experience of the use of osmic acid is 

 not very satisfactory, and he now sehlom uses it at all excepting when 

 such oi'jects as hair, bristles, <&c., are to be stained to show the 

 histological details. Without doubt one of the best objects to stain 

 by this means is Phronima sedentaria when every cell and nucleus 

 comes out most beautifully. According to Emery the yellow and red 

 fatty pigments of fishes can be better stained by osmic acid than by 

 any other means. The great drawback to the use of osmic acid is 

 that the preparations are very liable to get overstained, and thus a 

 precipitate is formed which interferes with the working of the 

 subsequent staining medium, for instance carmine or picro-carmiue. 

 There is, however, no difficulty in removing the osmic acid again 

 provided the ohject be at once immersed in 70 or 90 % alcohol. 

 Enough crystals of common salt are shaken into the liquid to cover 

 the bottom of the vessel and then with a pipette a few drops of 

 hydrochloric acid are aided until by stirring the liquid it is seen that 

 chlorine is being generated. This is easily recognised by its yellow- 

 green colour. If the bleachirg solution is placed on a water ba h 

 the process is considerably accelerated. Dr. Mayer has found that in 

 half-a-day he has been able to restore large Felagia, Cariniay 

 lililzostoma, &c., so that practically they were as good as ever. The 

 objects then require to be kept in pure alcohol again and the liquid 

 will require changing a few times to get rid of the smell of the 

 chlorine. This process of bleaching may also be used in getting rid 

 of natural pigments, as for instance in the eyes 'of insects and 

 Crustacea, but in these cases it is better first to cut the sections and 

 afterwards to bleach them, so that the chlorine gets a better chance 

 of acting on the pigments. 



Chromic Acid. — In the Zoological station at Naples, chromic acid 

 is now little used for invertebrates, as it has all the disadvantages of 

 osmic acid without possessing its advantages. It is, however, 

 frequently made use of, along with Kleinenberg's acid, where the 



