KILLING 9 



SUDDEN KILLING 



11. 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. We 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). 



For frog's eggs, iDring a large dish of water to the boil, remove bunsen 

 and then drop in the egg masses ; remove after ten minutes into 50 per 

 cent, alcohol (see also Hertwig, § 829). 



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

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

 by this method than by any other with which we are acquainted. 



12. 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 Lee very good results with 

 small Annelids and Hirudinea. Corrosive sublimate is another 

 excellent reagent for this purpose. 



NARCOTISATION 



13. Narcotisation is performed by adding some anaesthetic 

 substance very gradually, in very small doses, to the water con- 

 taining the animals, and waiting patiently for it to take effect 

 slowly. 



Peter Gray (Watson's Microscope Record, No. 35, 1935) 

 says that for Protozoa he tries new forms with the following 

 narcotics in this order : 10 per cent, methyl alcohol (not methy- 

 lated), 1 per cent, hydroxylaminc, 1 per cent, urethrane, Rousse- 

 let's solution, Corri's solution. " If these fail, hope may well be 

 abandoned." For Stalked Ciliates he uses Rousselet's solution, 



