XI ELECTRIC PROPERTIES OF THE NERVE 479 



the impulse which was started by the stimulus at x passes 

 under tlie terminal 6, that part of the nerve on which this 

 terminal rests, becomes momentarily less electrically 

 positive, that is to say becomes electrmdly negative as cmi- 

 pared ivith its condition before the passage of the impulse. 

 This statement holds equally good when the terminal b is 

 applied to any other point of the nerve, either towards A 

 or towards B, any difference in the result of stimulating 

 the nerve at x being merely one of degree (as regards the 

 extent to which the needle of the galvanometer moves), 

 and not of kind (as to the direction in which the needle 

 moves). Hence we may say without any possibility of 



Fig. 153.— To show Akkangement ot a Nerve and Galvanometer for 

 Experiments on the Elei;trical Properties of a Nerve. 



AB, a piece of nerve ; G, a galvanometer connected by wires and the 

 electrodes a, b, with the end B and the middle point C'of the nerve. 



doubt that when an impulse travels along a nerve each 

 point of the nerve becomes electrically negative as the 

 impulse reaches that point ; and conversely we may use 

 this electrical change in the nerve as unfailing evidence of 

 the passage of an imindse along it. Apart from this 

 electrical change we have no other means, such as exist in 

 the case of a muscle, of determining when a nerve enters 

 into a state of activity during the passage of an impulse. 



The Rate of TranBinission of a Nervous Impulse. — 

 By means of a complicated arrangement of apparatus it is 

 possible to determine very exactly the interval of time 

 which elapses between the moment at which the stimulus 

 is applied to the nerve at x (Fig. 153) and the instant at 



