1918] 



Bovard: Nervous Impulses in the Earthworm 



125 



cases. For the most part, impulses passed along the cord at the rate 

 of about 25 millimeters per second. This represents the mode of a 

 series of ninety-one measurements. Several observations showed good 

 transmission at the rate of 60 millimeters per second, and a few were 

 recorded in which the rate was very low, 10 millimeters per second 

 (fig. 13). 



Fig. 13. The frequency polygon which shows results of ninety-one measure- 

 ments of the speed of locomotor impulses through the nerve cord when the 

 peripheral nerves have been anesthetized. The mode lies between 20 and 30 

 millimeters per second. 



Conclusion. — The locomotor impulses show no definite speed. The 

 most interesting feature is the extreme variability of this movement. 

 In those cases where strength of stimulus is sufficient and other con- 

 ditions are right the speed may be as fast as 100 millimeters per 

 second, and again the speed may be so slow that it will die out in the 

 nerve cord without ever emerging from the anesthetized region. I 

 have taken the mode of the frequency polygon as against the average 

 which shows that ordinarily the speed is about 25 millimeters per 

 second. The slowness and variableness are the two main character- 

 istics. 



Rate of Impulses in the Giant Fibers 

 Problem. — How does the rate of transmission of locomotor impulses 

 compare with that of the giant fiber? Are the rates such that these 

 two phenomena can be ascribed to quite different systems of neurones ? 

 Discussion. — The method used to measure the rate of transmission 

 of impulses in the giant fibers was practically the same as that used 

 in measuring locomotor transmission, except that in this case it was 



