FIXING AND PRESERVATIVE MEDIUMS 39 



Hydroid polyps are, with rare exceptions, killed with the 

 same reagent at a time when the polyps are completely ex- 

 tended, which is effected by placing them in fresh sea-water. 

 After flooding the animals with the hot mercury, they should 

 be turned into a porcelain dish containing spring-water, and 

 left therein for five minutes to cool and wash them, after which 

 they should be transferred into weak alcohol, followed, as usual, 

 by other strengths up to 70 per cent. (Lo Bianco, p. 451). 



Embryos of dog-fishes and sharks are well fixed, says Lo 

 Bianco (p. 474), in a saturated solution of bichloride of mer- 

 cury, being left therein from five to fifteen minutes, and after- 

 wards well washed in the iodised alcohol (Formula 15), and, 

 unless required solely for histological purposes, they are put in 

 weak spirit, increased up to 70 per cent. Teleostean fishes 

 with a silvery skin, such as Trachypterus, are fixed and treated 

 in like manner, but leaving out the iodised alcohol. 



17. — Bichloride of Mercury and Sea-water 



Lo Bianco remarks (p. 445) that, with a saturated solution 

 in sea-water, he has obtained the best results with some of the 

 Protozoa as microscopical preparations, and instances amongst 

 them Trichophrya salparmn. 



It has been stated that solutions of bichloride of mercury, 

 either made with hot fresh or sea-water, or applied hot to 

 certain objects, especially plants, have more effect than made or 

 used cold ; if made or applied hot, however, care must be taken 

 not to inhale the vapour, and no metal must be used either 

 in their preparation or application. Earthenware vessels and 

 wooden or bone instruments alone must be used. 



18. — Bichloride of Mercury and Acetic Acid (Lo Bianco, p. 443) 



Bichloride of mercury (saturated solution) . . 100 parts 



Acetic acid (concentrated) . , . • 5° » 



