16 CHAPTER II. 



in commerce, is usually contaminated with HC1. It should 

 be dissolved in water (spring or sea water, according to the 

 habitat of the organisms in no case distilled water), and the 

 solution exactly neutralised by addition of carbonate of soda. 

 A 1 per cent, solution should be made up, and further diluted 

 for use. The organisms are placed in the diluted solution, 

 which may be taken of a strength varying from 0*1 percent., 

 used for thirty minutes or less (as for Infusoria), to 0*25 per 

 cent., used for from fifteen minutes to one hour (Hydra), 1 

 per cent., one half to two hours (Hirudo), or as much as ten 

 to twenty hours (Helix and Anodouta). 



It should be remembered that hydroxylamin is an extremely 

 powerful reducing agent. Care must therefore be taken not 

 to treat the paralysed animals with easily reducible fixing 

 agents, such as osmic acid, chromic acid, sublimate, chlorides 

 of gold or platinum, etc., unless it have been possible first to 

 sufficiently wash out the hydroxylamin with water. 



21. Chloride of Magnesium. TULLBERG (Arch. ZooL Exper. et Gen., 

 x, 1892, p. 11 ; Journ. Roy. Hie. Soc., 1892, p. 435) has obtained some 

 results with this salt. For Actiniae, a 33 per cent, solution of the salt is to 

 be very slowly added to the water containing the expanded animal, until the 

 vessel contains 1 per cent, of the salt (thus for one litre of sea water 33 c.c. of 

 the solution must be added). The addition must be made gradually, but it 

 must be effected within half an hour. Thirty minutes later the animal will 

 be found to be anaesthetised, and may be fixed. 



For terrestrial and fresh-water Invertebrates rather stronger solutions 

 should be used. 



EEDKNBAUGH (Amer. Natural., xxix, 1895, p. 399 ; Journ. 

 Roy. Mic. Soc., 1895, p. 385) has obtained good results by 

 means of Sulphate of Magnesia, either added in crystals to 

 the sea water containing the animals until a saturated solu- 

 tion is obtained, or in the shape of a saturated solution into 

 which they are thrown (Annelids). 



GEKAULD (Bull. Mus. Comp. ZooL, Harvard, xxix, 1896, 

 p. 123) has had good results with Caudina arenata by means 

 of the crystals added in teaspoonfuls. 



22. Poisoning by small doses of some fixing agent is sometimes a good 

 method. SALVATOEE LO BIANCO employs the following method for pre- 

 serving Ascidia and Rhopalsea in an extended state (Mitth. Zool. Stat. 

 Neapel, ix, 1890, p. 471). A little 1 per cent, chromic acid is poured on to 

 the surface of the water containing the animals, and allowed to slowly 



