10 KILLING 



until the snapping movements have slowed up, then very gingerly, 

 weak hydrogen peroxide. For Plmiarians he says 2 per cent, 

 chloral hydrate is the best, and for OUgochceta, chloroform. For 

 Polyzoa he uses menthol, overnight, then adds 40 per cent, 

 formaldehyde. 



C. F. Rousselet Solution (quoted from Carpenter's " The Micro- 

 scope ") is 2 per cent, solution of hydrochlorate of cocaine, 3 parts ; 

 methylated spirit (sic), 1 part ; water, 6 parts. This is the fluid used 

 for Rotifera especially. Failing genuine cocaine, Peter Gray recom- 

 mends stovaine. 



Dr. John Baker informs us that while Rousselet's fluid is good, 

 in most laboratories it will be found convenient to substitute 

 cocaine hydrochloride for the hydrochlorate and 90 per cent., 

 alcohol for methylated spirit. John Baker's modified formula, 

 which gives excellent results, is thus : — 



Cocaine hydrochloride, 2 per cent, aqueous . 3 c.c. 

 Alcohol, 90 per cent. . . . . .1 c.c. 



Distilled water . . . . . .6 c.c. 



For example, put Polyzoa in their natural water in a small watch- 

 glass and remove the water until there is only just enough to cover 

 them. Wait until they are well expanded. Add Rousselet's fluid, a 

 little at a time. (Do not let drops of the fluid fall on the water, as the 

 shock causes them to contract.) Continue until the watch-glass is 

 nearly full, and then wait for ten minutes. Then add 10 drops (or 

 less) of ^ per cent, osmium tetroxide solution, and leave for three 

 minutes. Wash repeatedly in changes of distilled water, and preserve 

 in 4 per cent, formaldehyde. 



14. Menthol. Now used with great success for anaesthetising 

 large marine animals. Place latter in clean vessel, and sprinkle 

 over surface of water, menthol crystals. As the latter dissolve 

 the animals expand. In from twelve to twenty-four hours they 

 may be transferred to a fixer. Very good for Anemones, Holo- 

 thuria, Ascidia and many Mollusca. (Personal communication 

 from Dr. E. J. Allen, Plymouth.) 



15. Nicotin in solution (Andres, Atti R. Acad, del Lincei, v, 

 1880, p. 9). Andres employs a solution of 1 grm. of nicotin in a 

 litre of sea water. The animal is placed in a jar containing half 

 a litre of sea water, and the solution of nicotin is gradually con- 

 ducted into it by means of a thread, acting as a syphon, of such a 

 thickness as to be capable of carrying over the whole of the 

 solution of nicotin in twenty-four hours. See also Mitth. Zool. 

 Stat. Neapel, Bd. ii, 1880, p. 123. 



16. Chloroform may be employed either in the liquid state 

 or in the state of vapour. The animals being extended, a watch- 

 glass containing chloroform may be floated on the surface of the 



