CHAPTER I 
ELECTRIC RESPONSE 
Conditions for obtaining electric response— Method of injury —Current of 
injury—Injured end, cuproid: uninjured, zincoid—Current of response 
in nerve from more excited to less excited—Difficulties of present nomen- 
clature—Electric recorder—T wo types of response, positive and negative 
—Universal applicability of electric mode of response—Electric response 
a measure of physiological activity—Electric response in plants. 
UNLIKE muscle, a length of nerve, when mechanically 
or electrically excited, does not undergo any visible 
change. That it is thrown into an excitatory state, and 
that it conducts the excitatory disturbance, is shown 
however by the contraction produced in an attached 
piece of muscle, which serves as an indicator. 
But the excitatory effect produced in the nerve by 
stimulus can also be detected by an electrical method. 
If an isolated piece of nerve be taken and two contacts 
be made on its surface by means of non-polarisable 
electrodes at A and B, connection being made with a 
galvanometer, no current will be observed, as both A 
and B are in the same physico-chemical condition. 
The two points, that is to say, are iso-electric. 
If now the nerve be excited by stimulus, similar 
disturbances will be evoked at both A and B. If, 
further, these disturbances, reaching A and B almost 
simultaneously, cause any electrical change, then, 
