CHARACTER OF THE CORTICAL CONTRACTIONS. 709 



than this ; and the same statement applies to the thinking the act of singing or 

 of playing a series of musical notes. 1 This would give, as the ordinary duration 

 of the activity of the cortical cell, when involved in the performance of the, 

 simplest psychological action, about 0*09 second ; but it is probable that 

 with practice, and under other favourable conditions, it might be further 

 reduced. 



If the surface of the motor region of the cortex be excited by a 

 faradic current, at a rate of rhythm either below or at about 10 to 12 

 per second, the muscles of the part with which the portion of the cortex 

 stimulated is in connection respond by contractions, which succeed one 



Fig. 323. — Myographic curves from hamstring of monkey. (A) 

 Natural contraction (voluntary) ; (B) contraction caused by 

 excitation of leg centre of cortex by rapid induced currents. 



another at the same rate as the excitation. If, however, the excitation 

 be more rapid than this, the response is no longer at the same rate 

 — as in the case of excitation of the motor nerve fibre — but tends to 

 reproduce the curve of voluntary contraction. 2 This is illustrated in 

 the tracings reproduced in Fig. 323. Of these A represents a voluntary 

 contraction of one of the hamstring muscles of a monkey, the tendon of 

 the muscle having been detached and fixed to the lever of a myograph ; 

 B represents the contraction of the same muscle, as provoked by 

 faradic excitation of the hamstring centre in the cerebral cortex, at a 



1 Ricbet, " Diet, de physiol.," Paris, 1898, tome ii. p. 10. Ricliet has also found, as the 

 result of direct experiment upon the cerebral cortex of the dog, that in this animal the 

 refractory period of the cortical cell is about - l sec. {Rep, of Toronto Meeting Brit. Ass. 

 Adv. Sc., London. 1897 ; Nature, London, 4th November 1897). 



2 Horsley and Sehafer, Journ. Physiol., Cambridge and London, vol. vii. Figs. 323 

 and 324 are reproduced from the tracings given in this paper. 



