24 FUNCTIONAL INERTIA 



they underlie a large number of neural disabilities. 

 Some of these are such as not being able to articulate 

 more than a certain number of syllables per second 

 (10 to ii per second), or to perform more than about 

 the same number of muscular twitches per second 

 with, e.g., the finger or the hand. 



Connected with the refractory period of the cells 

 of the spinal cord is the fact that the periodicity of 

 discharges to muscles in voluntary contraction is 

 something of the order of 10 to 12 (up to 18 rarely) 

 per second.* By voluntary impulses acting on the 

 cord this rate cannot be exceeded. 



Now Horsley and Schafer showed that if stimuli 

 at any rates higher than this spinal inherent rate, 

 say, of 50 a second were imposed on any part of the 

 encephalo-spinal tracts, the spinal discharges were 

 still at no greater rate than before (10 to 12 a second). 



Supposing, therefore, that it was ascertained that 

 the rhythm of discharge of voluntary impulses from 

 the cerebrum was something greater than 10 to 12 a 

 second, this would nevertheless be transmuted by the 

 functional inertia of the cells of the cord into a much 

 slower one, so slow that it could never fully fatigue 

 the muscles as is possible with the high frequency 

 stimulation of experimental tetanus. Thus there is 

 a neural, as well as a muscular, insusceptibility which 

 prevents exhaustion. 



Professor Schafer t in his article on " The Nerve 



* D. F.Harris, "The Time-Relations of the Voluntary Tetanus in 

 Man/' Journ. Phys., vol. xvii. No. 5, 1894. 



t "Text-book of Physiology." Edited by E. A. Schafer, vol. ii. 

 1900, p. 614. 



