406 



Profs. Y. A. Horsley and E. A. Schafer. [Dec. 10, 



per second, with very considerable regularity, although in a few 

 instances the rhythm may be a little slower or faster than these (eight 

 to thirteen per second are the extreme variations recorded). These 

 undulations have the same rhythm and character whatever the rate 

 of excitation (unless this be allowed to fall below about ten per 

 second). Moreover, precisely similar undulations are always visible 

 upon the myographic curve of all voluntary or spontaneous contrac- 

 tions (including reflex contractions) both in the lower animals and in 

 man. 



It is further noted that in the record of the contractions of epilepsy 

 there can frequently be seen marked upon the larger curves, produced 

 by the relatively slow clonic spasms, smaller undulations succeeding 

 one another with a rhythm of eight or ten per second. In some cases 

 the clonic contractions themselves may attain this rate, but they are 

 then always simple and without any indications of smaller waves. 



In a very few instances out of a very large number of experiments 

 there occurred upon the tracings obtained as the result of rapid exci- 

 tation of the cortex cerebri, corona radiata, and medulla spinalis, 

 besides the usual well marked undulations of the rate of about ten per 

 second, other very minute waves upon these undulations correspond- 

 ing in rhythm with the rate of excitation. These were the only 

 occasions in which we have obtained results at all similar to those 

 mentioned by Franck and Pitres. 



The accompanying tracings will serve to indicate the general 

 nature of our results. Tracings A, B, C, and D are all taken from 

 the same animal (dog). Tracing A shows the myographic curve 

 obtained during excitation of the cortex cerebri (sigmoid gyrus), as 

 well as the succeeding epilepsy. Tracing B was that obtained on 

 excitation of the subjacent corona. Tracing C resulted from excita- 

 tion of the cat spinal cord. Tracing D from excitation of the motor 

 nerve. The excitation was produced by varying the current through 

 the primary coil of a sliding inductorium by a metallic reed vibrating 

 thirty times per second in the case of A, C, and D, and forty per 

 second in the case of B. The vertical lines mark seconds. E is 

 the tracing of a voluntary muscular contraction in man (opponens 

 pollicis). 



Conclusions. — The main conclusions to be drawn from the results 

 of our experiments appear to be these: — 1. That the normal rate of 

 discharge of nervous impulses from the motor nerve-cells of the 

 spinal cord along the motor nerve-fibres is approximately ten per 

 second.* 2. That in the case of nervous impulses reaching these- 



* This conclusion is supported by the fact that the rhythm of a clonus (e.g., ankle- 

 clonus) depending upon the activity of the spinal cord is also about 8 or 10 per 

 second, and that the rhythm of strychnine-tetanus in the frog, as indicated by the 

 electrical variations of the muscle-current, has about the same rate (Loven). 



