10 KILLING. 



The difficulty consists in hitting off the right temperature, 

 which is of course different for different objects. I think that 

 a temperature of 80 to 90 C. will generally be amply suffi- 

 cient, and that very frequently it will not be necessary to go- 

 beyond 60 C. An exposure to heat of 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 coagulated 

 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. 



8. Animals that contract but slowly, such as Alcyonium and 

 Yeretillum, and some Tunicates, such as Pyrosoma, are very 

 well killed by throwing them into some very quickly acting 

 fixing liquid, either used 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. See 

 "Acetic acid " and " Tunicata." Corrosive sublimate is another 

 excellent reagent for this purpose. 



Narcotisation. 



9. The secret of narcotisation consists in adding some 

 anaesthetic substance very gradually, in very small doses, to 

 the water containing the animals, and waiting patiently for 

 it to take effect slowly. 



THE TOBACCO-SMOKE METHOD for Actiniae (HEETWIG, Die Actinien, 

 1879) used to be practised as follows : A dish containing the animals in 

 water is covered with a bell-glass, under which passes a curved glass or 

 rubber tube, which dips into the water. Tobacco smoke is blown into the 

 water for some time, through the tube, and the animals are then left for 

 some hours in order that narcotisation may become fully established. The 

 animals are irritated from time to time by touching a tentacle with a needle. 

 As soon as it is observed that an animal begins to react slowly, that is to 

 say as soon as it is found that the contraction of the tentacle does not begin 



