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Nervous Rhythm arising from Rivalry of Antagonistic Reflexes : 

 Reflex Stepping as Outcome of Double Reciprocal Innervation. 

 By C. S. Sherrington, F.E.S. 



(Received February 3,— Read February 20, 1913.) 



(From the Physiological Laboratory, University of Liverpool.) 



i. 



The observations with which the present communication deals were 

 met with in experiments continuing those on reciprocal innervation of 

 symmetrical muscles. In my previous paper on that subject* it had been 

 reported that in regard to symmetrical extensors of the knee the ratio 

 borne by intensity of the ipsilateral inhibition to the contralateral excitation 

 is such that with equal stimuli to right and left symmetrical afferent nerves 

 tbere is inhibitory suppression of contraction in both the muscles. In 

 other words, under double reciprocal innervation the ipsilateral inhibition 

 by each nerve completely overcomes tbe contralateral excitation of the 

 other. It was shown that this mutual suppression holds over a wide range 

 of the scale of intensities of stimulation. It was also shown that with quite 

 weak stimuli a simultaneous stimulation of both nerves, stimuli being equal in 

 intensity, often results in concurrent contraction of both muscles. Indeed, 

 with quite weak stimuli, the effect of stimulation of each afferent nerve by 

 itself is, in the decerebrate preparation, usually contraction of the ipsilateral 

 as well as of the contralateral muscle. 



This being so, it is evident that at some point in the scale of intensities 

 of stimulation there should be a place below which contralateral excitation 

 is stronger than ipsilateral inhibition, whereas above it ipsilateral inhibition 

 is stronger than contralateral excitation. 



My further experiments were directed to finding where on the intensities- 

 scale this point actually lies. In prosecuting this search there began to be 

 met instances of rhythmic contraction of exceedingly pronounced character. 



Method employed. 



The mode of preparation when the knee extensor was observed was as follows : — The 

 animal (cat) was decerebrated under deep chloroform and ether narcosis. In both limbs 

 all muscles were then detached from the great and lesser trochanters and intertrochanteric 

 line. The insertions of right and left iliopsoas, psoas parvus, and tensor fascioe femoris 

 were then carefully resected up, and the origin of rectus femoris right and left. In both 

 limbs the following nerves were severed : popliteal, small sciatic, hamstring, external 



* Supra, p. 219. 



