Activities of the Mid-Brain. 



153 



not usually sustained on withdrawal of the contralateral "background" 

 stimulus. Where extensor restitution of contraction occurs the withdrawal 

 of the contralateral stimulus is followed by extensor after-discharge. In one 



Fig. 3— Experiment M, XXIV, record 311, 8362 ; 31.3.13.— Macaeus rhesus. The dorsal 

 spinal roots of the left (recording) fore limb divided in May, 1912. A reaction 

 obtained 44 minutes after decerebration. 



The first reaction (a) is a compound one with an ipsilateral " background." 

 During double stimulation there is flexor relaxation, but no extensor contraction. 

 The latency of the flexor relaxation is great. On withdrawal of the contralateral 

 stimulus there is flexor restitution of contraction which occurs as a very sudden 

 movement. On withdrawal of the ipsilateral " background " stimulus there is a 

 marked flexor after-discharge. The sudden drop in the flexor after-discharge seen 

 about 3 mm. before the final ordinate in reaction (a) occurred during a period of 

 15 seconds in which the kymograph was stopped — it therefore represents a very 

 slow movement. 



The second reaction (6) is a compound one in which the contralateral reaction is 

 the "background." During double stimulation flexor contraction and extensor 

 relaxation occur. But on withdrawal of the ipsilateral interrupting stimulus (at 

 /<, h') there continues a flexor after-discharge. On withdrawal of the contralateral 

 " background " stimulus this disappears. 



case, where flexor relaxation occurred on withdrawal of the interrupting 

 ipsilateral stimulus, there yet occurred flexor rebound on withdrawal of the 

 contralateral " background " stimulus. There the same phenomenon occurred 



VOL. LXXXVII. — B. M 



