KILLING AND FIXATION 345 



such methods are suitable only for those who have at 

 their disposal a regular laboratory, on shore or on 

 board a yacht ; it is even to be hoped that these latter 

 instructions may prove of value to the smaller fixed 

 marine laboratories in far-away seas. 



The successful preservation of marine organisms 

 depends not only upon selecting the right method, but 

 frequently upon a certain amount of practice. A 

 naturalist going on a foreign cruise, who is not experi- 

 enced in preservation, is advised to take a course of 

 instruction at a marine laboratory, where he would 

 soon learn the right way of setting to work. 



It is quite easy to kill animals by simply placing them 

 in formalin or alcohol, but the results are not always 

 satisfactory. Some may have a lifelike appearance, 

 whilst others may contract into a lump, or even break 

 up into pieces ; hence it may be necessary to anaesthe- 

 tize the contractile animals with cocaine, menthol, or 

 some other narcotic before killing them. There are 

 two methods of killing animals, the results of which are 

 quite different. The one is simply to destroy the life 

 of the animal by anaesthetics, without at the same time 

 destroying the life of the tissues, which may survive 

 for some time after the death of the animal. This 

 method is quite suitable for specimens intended for 

 museums and for identification. The other method 

 is to kill the tissues first by certain chemicals, and the 

 death of the tissues causes the death of the animal. 

 When animals are wanted for minute microscopical 

 investigations this latter method is always used, and 

 its success depends upon killing the cells of the tissues 

 before they have time to undergo any change, by 

 chemicals which do not produce a visible change within 

 the cell. The process of " fixing " the contents of the 

 cell and the shape of the cell is called " fixation." An 



