12 KILLING. 



Sudden Killing. 



13. Heat.- -The application of Heat affords a means of killing 

 suddenly. By it the tissues are more or less fixed at the same time 

 that somatic death is brought about. 



The difficulty consists in hitting off the right temperature, which 

 is of course different for different objects. I think that 80 to 90 C. 

 will generally be amply sufficient, and that very frequently it will 

 not be necessary to go beyond 60 C. An exposure to heat for a few 

 seconds will generally suffice. 



Small objects (Protozoa, Hydroids, Bryozoa) may be brought into a 

 drop of water in a watch-glass or on a slide, and heated over the flame 

 of a spirit-lamp. For large objects, the water or other liquid employed 

 as the vehicle of the heat may be heated beforehand and the animals 

 thrown into it. 



As soon as it is supposed that the protoplasm of the tissues is coagu- 

 lated throughout, the animals should be brought into alcohol (30 to 70 

 per cent, alcohol) (if water be employed as the heating agent), 



An excellent plan for preparing many marine animals is to kill them 

 in hot fresh water. Some of the larger Nemertians are better preserved 

 by this method than by any other with which I am acquainted. 



14. Slowly Contracting Animals. Animals that contract but 

 slowly, such as Alcyonium and Veretillum, and some Tunicates, such 

 as Pyrosoma, are very well killed by throwing them into some very 

 quickly acting fixing liquid, used either hot or cold. Glacial or very 

 strong acetic acid (VAN BENEDEN'S method) is an excellent reagent 

 for this purpose ; it may be used, for example, with some Medusae. 

 After an immersion of a few seconds or a few minutes, according to 

 the size of the animals, they should be brought into alcohol of at 

 least 50 per cent, strength. Lemon juice employed in this way has 

 given me very good results with small Annelids and Hirudinea. 

 Corrosive sublimate is another excellent reagent for this purpose. 



Narcotisation. 



15. Narcotisation is performed by adding some anesthetic sub- 

 stance very gradually, in very small doses, to the water containing 

 the animals, and waiting patiently for it to take effect slowly. 



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, Holothuria, Ascidia and many Mollusca. (Personal 

 communication from Dr. E. J. ALLEN, Plymouth.) 



16. Nicotin in solution (ANDRES, Atti R. Accad. dei Lincei, v, 1880, 

 p. 9). Andres employs a solution of 1 gramme of nicotin in a litre 



