318 



PRACTICAL PHYSIOLOGY 



chamber without any escape into the moist chamber. Minimal stimuli 

 are obtained for the nerve lying on the two pairs of electrodes, and 

 the contraction is recorded upon a stationary drum. A stream of 

 carbon dioxide is passed through the gas-chamber ; the minimal 

 stimulus is no longer effective at (5), but is still adequate at (a). The 

 carbon dioxide has locally lowered the excitability, but has not 

 affected the conductivity of the nerve. Fresh air is drawn through 

 the gas-chamber ; the stimulus at (b) will again become effective. 



Pio. 196. Diagram of the experiment upon the influence of carbon dioxide, ether 

 and chloroform on the excitability and conductivity of nerve. 



This experiment is repeated with ether or chloroform, and it is 

 found that both the excitability and conductivity are diminished. 

 The removal of the vapour by a current of fresh air will restore both 

 the excitability and conductivity. Prolonged action of the anaesthetic 

 will produce poisoning, arid in this respect chloroform is much the 

 more toxic of the two. 



CHAPTER XIV. 



THE EFFECT OF A CONSTANT ELECTRICAL CURRENT UPON THE 

 EXCITABILITY AND CONDUCTIVITY OF NERVE. 



THE passage of a constant current produces changes in the excitability 

 of nerve, at the anode there is a condition known as anelectrotonus, 

 the excitability is diminished ; at the kathode there is an increase in 

 excitability, a state of katelectrotonus. The conductivity is also 

 affected, there is a fall in both the anodic and kathodic regions. 

 These effects can be shown by the following experiment. 



