A NERVOUS IMPULSE 



481 



it becomes a simple matter to calculate the rate at which 

 the impulse travels from 1/ to x. The result thus 

 obtained agrees quite closely with the one arrived at in 

 the experiment previously described in which a gaWano- 

 meter was used, namely 28 metres or 90 feet per second. 



The rate at which an impulse travels along a nerve is 

 closely dependent on the temperature of the nerve, and 



FiQ 154 -Arrangement of Nerve, Muscle and Lever for deter- 

 j.ia. -^^,^1^0 THE Velocity of a Nervous Impulse. 



f femur ■ vi muscle ; t.a, tendon ; I, lever, movable about the end 6 ; 

 J. weight to keep the Muscle stretched ; n, the nerve ; x and y, the two 

 points at which the nerve is stimulated. 



diminishes as the nerve is cooled ; thus, by cooling a frog's 

 nerve the rate may be reduced to as little as 1 metre 

 (3 feet) per second. Hence it is not surprising that when 

 experiments are made on the nerves of a warm-blooded 

 human being, the rate of transmission is found to be 

 somewhat greater, viz., about 100 metres (or over 300 

 feet) per second, than in the cold-blooded frog. 



The most efficient stimulus which can be artificially 



I I 



