BLE CLERIC: RESPONSE 9 
effect produced at A, the existing difference of 
potential may thus be reduced, with a consequent 
diminution of the current of injury. During stimula- 
tion, therefore, a nerve exhibits a negative variation. 
We may express this in a different way by saying 
that a ‘current of action’ was produced in response 
to stimulus, and acted in an opposite direction to 
the current of injury (fig. 2,4). The action current 
in the nerve is from the relatively more excited to the 
relatively less excited. 
Difficulties of present nomenclature.—We shall deal 
later with a method by which a responsive current of action 
is obtained without any antecedent current of injury. ‘ Nega- 
tive variation’ has then no meaning. Or, again, a current of 
injury may sometimes undergo a change of direction (see note, 
p. 12). In view of these considerations it is necessary to 
have at our disposal other forms of expression by which the 
direction of the current of response can still be designated. 
Keeping in touch with the old phraseology, we might then 
call a current ‘negative’ that flowed from the more excited 
to the less excited. Or, bearing in mind the fact that an 
uninjured contact acts as the zinc in a voltaic couple, we 
might call it ‘zincoid, and the injured contact ‘cuproid.’ 
Stimulation of the uninjured end, approximating it to the 
condition of the injured, might then be said to induce a 
cuproid change. 
The electric change produced in a normal nerve by stimu- 
lation may therefore be expressed by saying that there has been 
a negative variation, or that there was a current of action 
from the more excited to the less excited, or that stimulation 
has produced a cuproid change. 
The excitation, or molecular disturbance, produced 
by a stimulus has thus a concomitant electrical expres- 
