1913.] 



arising from Rivalry of Antagonistic Reflexes. 



235 



for in my experiments. When pursuing adjustments of the stimuli in 

 order to arrive at determination of this it was found that rhythmic alter- 

 nating contraction and relaxation, reciprocal in direction in the two muscles, 

 appeared directly both stimuli were employed concurrently, though quite 

 absent under either stimulus alone. 



During these rhythmic reactions a glance at the preparation was enough 

 to show that, although only the one thigh muscle remained in each limb, 

 the animal was stepping with both limbs, usually at a quick walking pace, 

 and whether the muscle remaining were an extensor or a flexor. It began to 

 step as soon as ever the two antagonistic stimuli were concurrently com- 

 bined, and it ceased to step directly their union was dissolved. Fig. 1 

 exemplifies this. There it is seen that it did not matter whether the 

 combination were made by adding the inhibitory stimulus to the excitatory 

 already in action, or the excitatory to the previously-acting inhibitory ; in 

 either case the stepping did not occur under either stimulus acting alone, 

 yet ensued directly the two opposed stimuli were in action together. 

 Conversely, on withdrawing either of the stimuli and leaving the other one 

 in operation the stepping immediately ceased, each limb then passing into 

 either steady contraction or steady relaxation, according as the remaining 

 stimulus was contralateral to it or ipsilateral. 



Nervous inhibition seems in many ways the exact opposite and counter- 

 part of nervous excitation. And since the process of nervous excitation is 

 certainly rhythmic, its natural rhythm in mammalian motoneurones being 

 probably about 50 impulses per second (Piper),* it may be argued that the 

 process of nervous inhibition is probably similarly rhythmic. Yet in com- 

 parison with the slow periods of many rhythmic muscular acts, for instance 

 those of breathing and stepping, a rhythmic frequency of 50 per second can 

 be considered as tantamount to continuous and steady operation. It is a 

 question how there are developed from such minutely oscillatory nervous 

 discharge those coarser rhythmic actions with periods recurring once in 

 3 sees, as in breathing, or once a second as in the step, or four times 

 a second as in the scratch reflex. The suggestion has often been made that 

 such rhythmic nervous actions are the result of the concurrent action of two 

 opposed nervous forces, the outcome of a constant opposition or resistance 

 acting against a constantly discharging nervous activity. '"How can the 

 constant motion of the nervous fluid be changed to a periodic motion ? 

 When a conductor of electricity is held at some distance from the electric 



II. 



* < 



Elektrophysiologie menschlicher Muskeln,' Berlin, 1912. 



VOL. LXXXVI. — B. 



S 



