IRRITABILITY AND CONDUCTIVITY 185 



the vertical line marked by it when the current 

 was made, and then stimulating the muscle to 

 contract. The ordiuate drawn hy the muscle 

 lever (the drum being still at rest) will be 

 synchronous with the ordinate drawn by the 

 signal during the experiment.] 



It will be found that the interval between 

 stimulation and contraction is greater when the 

 nerve is stimulated far from the muscle than it 

 is on stimulation near the muscle. The differ- 

 ence is the time occupied by the passage of the 

 excitation wave along the nerve between the 

 electrodes. 



Measure the length of nerve between the elec- 

 trodes, and calculate the speed of the nerve im- 

 pulse per second. 



It is assumed in this method that the interval 

 between the closure of the primary circuit and 

 the beginning of the nerve impulse is the same 

 in both instances, and that the interval between 

 the arrival of the impulse in the muscle, and the 

 visible change of form, is likewise the same in 

 both. If the mean and the probable deviation of 

 a series of measurements are taken, a fairly accu- 

 rate result may be expected. A better method, 

 however, is to record the passage of the negative 

 variation over a measured length of nerve by 

 photographing the meniscus of the capillary 



