14 KILLING. 



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. 



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

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

 serving Ascidise in an extended state. A 1 per cent, solution of chromic acid 

 acidulated with acetic acid is poured on to the surface of the water contain- 

 ing the animals, and allowed to diffuse slowly through it. The operation 

 takes four or five days (v. GAEBINI, Manuale per la Technica Mod. del 

 Microscopic, p. 168). 



Osmic acid, or Kleinenberg's solution, is sometimes employed in the 

 same way. 



I have seen Medusae killed in a satisfactory manner by means of crystals 

 of corrosive sublimate added to the water containing them. 



Morphia, Ourare, Strychnin, Prussic Acid, and other paralysing 

 drugs have also been employed. 



19. Asphyxiation may be sometimes successfully practised. 

 Terrestrial Gastropods may be killed for dissection by putting 

 them into a jar quite full of water that has been deprived of 

 its air by boiling, and hermetically closed. After from 

 twelve to twenty-four hours the animals are generally found 

 dead and extended. The effect is obtained somewhat quicker 

 if a little tobacco be added to the water. 



Good results are sometimes obtained with aquatic animals 

 by simply leaving them to exhaust the oxygen of the water in 

 which they are contained. I have sometimes succeeded with 

 Holothuriae and other Echinoderms in this way ; and WAED 

 (see Amer. Nat., xxv, 1891, p. 398) has succeeded with 

 Hydroids, Actiniae, and similar forms. If the animals be 

 found to be imperfectly expanded when narcosis has set in, 

 they may be got to expand by putting them back for a short 

 time into pure sea-water ; and as soon as they are expanded 

 should be quickly thrown into some rapidly-killing reagent. 



Carbonic Acid Gas has been recommended (by FOL, Zool. Anz., 128, 

 1885, p. 698). The water containing the animals should be saturated with 

 the gas. The method is stated to succeed with most Coelenterata and 

 Echinodermata, but not with Molluscs or Fishes. It has not been found 

 successful at the Naples laboratory. 



20. Marine Animals are sometimes successfully killed by 

 simply putting them into fresh water. 



Warm Water will sometimes serve to immobilise and even 

 kill both marine and fresh-water organisms. 



