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 exactby neutralised by addition of carbonate of soda. 

 A 1 percent, 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 (VI percent., 

 used for thirty minutes or less (as for Infusoria), to (V25 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 Anodoiita). 



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. Mic. 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. 



REUKNBAUGH (Aincr. Natural., xxix, 1895, p. 399; Journ. 

 li'ui/. M!<-. >SV-., 1895, p. 385) has obtained good results by 

 means of Sulphate of Magnesia, either added in crystals to 

 the >c;i water containing tin- animals until a saturated solu- 

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

 wliirli ihcy ;MV thrown (Annelids). 



(!KI:AULD (Bull. Mn*. Comp. /<<,nl. } Harvard, xxix, 1896, 

 p. 123) has Ii;id good results with ('umlhia arena ta by means 

 i>!' I lie crystals nddrd in teaspoonfuls. 



22. Poisoning by small dnsrs of sonic fixing agent is sometimes a good 

 mrili, i.l. SALVATOEE LO ]'.I\MO employs tlic following method for pre- 

 serving Axuiilin and l{lti>j>'<l;> in an extended state (Mitth. Zool. Stat. 



/"I. \\. isnn, ].. 171 |. A little 1 per ..-cut. chromic acid is poured on to 

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



