124 PHYSIOLOGY OF MUSCLES AND KERVES. 



cannot be shown with our present apphances. As 

 motions of the smallest particles (molecules) probably 

 take place in the nerve, though the external form 

 remains unaltered, and therefore no work worthy of 

 consideration is accomplished, it is easily intelligible 

 that these processes may be accompanied only by ex- 

 tremely slight changes in the constituent parts. 



The speed with which death and the changes in 

 excitability connected with death take place mainly 

 depends, apart from the length of the nerve, on the 

 temperature. The higher the temperature the more 

 quickly does the nerve die. At a tempei*ature of 44° C. 

 death occurs in from ten to fifteen minutes ; at 75° C. 

 in a few seconds ; and in the average temperature of a 

 room the lower ends of a long sciatic nerve may re- 

 tain their excitability for twenty-four hours or longer 

 after extraction and preparation. Drying at first in- 

 creases the excitability, but afterwards rapidly decreases 

 it. Chemical agents, such as acids, alkalis and salts, 

 destroy the excitability the more rapidly the more 

 concentrated they are. In distilled water the nerve 

 swells and rapidly becomes incapable of excitement. 

 There are, therefore, certain densities of salt solutions 

 in which the nerve remains excitable longer than in 

 thinner or in more dense solutions. A solution of com- 

 mon salt of 0'6 to 1 per cent., for instance, has almost 

 no effect on 'a nerve submerged in it, and preserves the 

 excitability of this nerve about as long as damp air. 

 Pure olive oil, if not acid, may also be regarded as 

 innocuous. These are, therefore, used when the in- 

 fluence of different temperatures on the nerve is to be 

 studied. 



