564 



PHYSIOLOGY 



CHAP. 



too absolute, was subsequently modified by the authors themselves, 

 who found that the ascending line of a cortico-muscular tetanus is 

 invariably notched, the fusion of contractions not being always 

 complete if the stimuli are sent at a rate sufficient to produce 

 tetanus when applied to the muscle or its motor nerve. 



The later work of Horsley and Schiifer (1886) led to more 

 exact results, which are to some extent directly contradictory of 

 the statements of Fran^ois-Franck and Pitres. In experimenting 



FIG. 2S7. Myographic curves from hamstring of monkey. (Horsley and Schnfer.) A, natural 

 contraction (voluntary); B, contraction caused by excitation of cortical leg centre by rapid 

 induced currents. 



on monkeys, dogs, cats, and rabbits they found that when the 

 excitable zone of the cortex was stimulated with faradic currents of 

 a frequency of 10-12 per second the muscle reacted with rhythmical 

 contractions of the same rhythm as the current. But this 

 synchronism ceases when the frequency of stimulation exceeds 

 that limit ; the contraction curve no longer shows fusion of 

 the contractions, that is, complete tetanus, but it reproduces the 

 rhythmical oscillations of voluntary movements (Fig. 287). 



From these results as a whole it seems reasonable to conclude 

 that the active state aroused in the cells of the cortex by direct 

 artificial stimulation is analogous to, if not identical with, the 



