NARCOTISATION. 9 



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 

 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 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 70 

 per cent, strength. Corrosive sublimate is another excellent 

 reagent for this purpose. See 45, 46. 



Narcotisation. 



9. The secret of narcotisation consists in adding some anaes- 

 thetic 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) is frequently 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 



