242 Prof. C. S. Sherrington. Nervous Rhythm [Feb. 3, 



stimulus no obvious change occurs, because the stimulus is inhibitory and 

 under it the muscle is already relaxed and relaxes no further and no less on 

 cessation of the excitation, a " lengthening reaction " having occurred at end 

 of the r. nerve stimulation. 



Three seconds later the left nerve stimulation is recommenced ; steady con- 

 traction of r. muscle is reassumed; 1. muscle being already relaxed the 

 inhibitory effect there is not apparent, although really fully existent, as 

 subsequent events show. The 1. nerve stimulus is here the pre-current 

 stimulus, and under it no rhythm of any kind appears in either muscle 

 any more than did under r. nerve stimulus in the preceding observation. 

 But on then applying stimulation of r. nerve, that of 1. still continuing as 

 before, rhythmic stepping at once appears. It begins synchronously in 

 right and left muscles, the opening phase being contraction, i.e. extension 

 of limb, in the left muscle, and relaxation, i.e. flexion of limb, in the 

 right muscle. On withdrawing the r. nerve stimulus, about 6 sees, later, 

 when the last step of a sequence of six has been nearly completed, the 

 stepping ceases abruptly with completion of that step. The right muscle 

 then reverts to steady contraction, the left to full relaxation. This 

 resumption is, of course, the effect of the still-continuing 1. nerve stimula- 

 tion, and guarantees that the stimulation of that nerve has remained 

 effective throughout. Eather more than a couple of seconds later the 

 1. nerve stimulation is withdrawn and the contraction of right muscle, in 

 consequence, shows decline, modified, however, by the shortening reaction of 

 the plastic tonus. 



Two seconds later r. nerve's stimulation is once more commenced. It 

 evokes steady contraction of 1. muscle and, synchronously with that, full 

 inhibitory relaxation of r. muscle. During the 3 - 5 sees, for which this 

 stimulus remains thus in operation by itself, the steady reciprocal reaction 

 of the two muscles is maintained unchanged. The stimulation of 1. nerve 

 is then commenced, that of r. nerve continuing unaltered. Synchronous 

 stepping, reciprocal in direction in the two muscles, sets in at once. Here 

 the opening phase in each muscle is the reverse of that in the previous 

 observation. The 1. nerve stimulus is maintained in concurrence with that 

 of r. nerve for 7 sees., and during that period a sequence of six complete 

 and regular steps is performed by each muscle. Stimulation of 1. nerve is 

 then withdrawn, and both muscles at once revert to the non-rhythmic 

 steady state they exhibited previously under stimulation of r. nerve alone, 

 r. muscle being in steady relaxed condition, and 1. muscle held s.teadily con- 

 tracted. Later, the stimulation of r. nerve is itself finally withdrawn ; 

 the contraction of 1. muscle then at once begins to decline into pure stato- 



