268 



Reciprocal Innervation oj Antagonistic Muscles. 



parts of one and the same reflex. In harmony with this stands also 

 the fact that when the one or the other afferent is made prepotent hy suitably 

 increasing the intensity of its stimulus, the prepotency obtains both for exci- 

 tatory influence and inhibitory influence alike. The reflex produced by either 

 afferent is, in fact, a reflex of simultaneous double sign (+ reflex). And in 

 the observations furnished there is a good deal of evidence suggesting that 

 the relation between the intensity of the excitatory part of the reflex and the 

 inhibitory is such that the intensity of the one increases proportionally with 

 that of the other. The rhythm of the inhibitory effect in the motoneurones 

 of one muscle appears also to be synchronous with that of the excitatory 

 effect in the motoneurones of the antagonist muscle, to judge by the rhythmic 

 tremor not unfrequently evident on the myograph tracings. Observation IV 

 of fig. 9b furnishes an illustration of this. 



VII. — It was shown previously that after reflex inhibition of the moto- 

 neurones of the extensor muscle there ensues, in decerebrate rigidity, on 

 withdrawal of the inhibitory stimulus, a contraction of the muscle. This is 

 the rebound contraction which I attribute to " successive spinal induction." It 

 may far exceed in intensity the tonic contraction which existed prior to the 

 inhibition. The question arises as to what state obtains in the flexor muscle 

 when this rebound contraction of its antagonist occurs. With the double 

 myograph recording both extensor and flexor simultaneously, this relation can 

 be studied. Fig. 9a, Obs. I and II, and fig. 10, r, give instances of the time 

 relations observable. On withdrawal of the ipselateral stimulus, the flexor 

 contraction passes off, and at the same time there takes place the rebound 

 contraction of the extensor. Often a relatively long latency period intervenes 

 between the cessation of the stimulus and the onset of the extensor's rebound 

 contraction. Similarly it is not unusual for the contraction of the flexor to 

 outlive the duration of the excitatory stimulus for a certain time, the flexor 

 motoneurones exhibiting after discharge. The simultaneous record of the two 

 muscles shows that the rebound contraction of extensor synchronises with the 

 dying out of the after-contraction of the flexor ; the after discharge (rebound) 

 of the extensor motoneurones comes into action as that of the flexor moto- 

 neurones passes off. Therefore, in the after-action shown by these antago- 

 nistic centres, there is evident the same kind of reciprocal activity as is seen 

 in their reaction under stimuli in application at the time. In after-discharge 

 and in tonus, as also when reacting to ordinary reflex stimulation, reciprocal 

 innervation seems to hold good in regard to the mutual relation between the 

 motor centres of the antagonistic muscles. 



