CHAPTER II. 



KILLING. 



10. IN the majority of cases, the first step in the prepara- 

 tion of an organ or organism consists in exposing it as 

 rapidly and as completely as possible to the action of one of 

 the Fixing Agents that are discussed in the next chapter. 

 The organ or organism is thus taken in the normal living 

 state ; the fixing agent serves to bring about at the same 

 time, and with sufficient rapidity, both the death of the 

 organism and that of its histological elements. 



But this method is by no means applicable to all cases. 

 There are many animals, especially such as are of a soft con- 

 sistence, and deprived of any rigid skeleton, but possessing 

 a considerable faculty of contractility such as many Coalen- 

 terata, Bryozoa, and Serpulida, for instance which if thus 

 treated contract violently, draw in their tentacles or branchiae, 

 and die in a state of contraction that renders the preserved 

 object a mere caricature of the living animal. In these 

 cases special methods of killing must be resorted to. 



Sudden Killing. 



11. Heat. Speaking generally, there are two ways of 

 dealing with these difficult cases. You may kill the animal 

 so suddenly that it has not time to contract ; or you may 

 paralyse it by narcotics before killing it. 



The application of Heat is a good means of killing 

 suddenly. It has the great advantage of allowing of good 

 staining subsequently, and of hindering less than any other 

 method the application of chemical tests to the tissues. By 

 it the tissues are 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 



