246 



Prof. C. S. Sherrington. Nervous Rhythm 



[Feb. 3, 



r. at value 13 does suppress all contralateral excitatory effects from I. at 

 value 16. The r. muscle therefore in fig. 5 does not step. But in the 

 1. muscle i.'s stimulus value 16 restrains the contralateral excitatory effects of 

 r.'s stimulus value 13 even less than was the case when l.'s stimulus was 

 value 17 and r's stimulus value was 16. Hence the 1. muscle steps faster in 

 fig. 5 than in fig. 4, r.'s excitatory effect breaking through l.'s inhibition more 

 rapidly and frequently. This quickening of the step under the stronger 

 stimulus harmonises with the observation that though the direct faradisation 

 required to excite stepping from a point in the cross-section of the cervical 

 spinal cord is of quite weak intensity, the rate of the stepping of hind limb so 

 produced increases, ceteris -paribus, with the intensity of the faradic 

 stimulus. 



As to the strength of the antagonistic stimuli which by their concurrence 

 evoke the stepping, the phenomenon, in my experience, is not obtainable 

 with strong stimuli. With stimuli just above threshold intensity I have 

 at times seen traces of the rhythmic undulation ; but attempts to develop 

 it with such very weak stimuli have not so far attained much result. Stimuli 

 rather stronger than such but on the weak side of moderate have yielded 

 the best results. Weakening the stimuli beyond that point gives a 

 rhythm not only slower but more irregular with waves of varying 

 amplitude (fig. 6a), and a tendency to pauses between some of the beats. 

 On the other hand, with too strong stimuli there is a tendency for the 

 rhythmic reaction to be suppressed in one or other member of the muscle-pair, 

 and for it to be represented in the other member by a few sharp somewhat 

 irregularly explosive beats separated by longish unequal intervals (fig. 6b). An 

 idea of the range of intensities suitable may be afforded by the data of an 

 experiment. In the experiment from which figs. 6a and 6b, and also fig. 4, 

 have been taken, the threshold value for reflex effect both ipsilateral and 

 contralateral lay for r. nerve at 17'8 cm. and for 1. nerve at 19"2 cm. This 

 seems high, but it must be remembered that a resistance box of 

 100,000 ohms was included in each circuit. Slight but distinct rhythmic 



stepping was obtained by the combination r. at 16 cm. and 1. at 18 cm. 



no stepping with right muscle, and merely two short unequal steps with 



2. Strength of Stimulus. 



