226 



Prof. C. S. Sherrington. Reciprocal [Nov. 13, 



the two symmetrical extensors exhibit inhibitory relaxation. It is to be 

 noted that if the initial condition of the muscles be full repose, e.g. —10 in the 

 above notation, then in the above instance the symmetrical extensors (as 

 well as the flexors) enter upon a certain degree of contraction, namely —4, 

 full relaxation being —10. In any case the double stimulus gives an 

 identical reflex effect on the symmetrical muscles, though the reflex effect 



still remains reciprocal as regards the pairs of antagonistic muscles. Under 

 the double stimulus the reflex effect becomes symmetrical and identical in 

 the two limbs, although under either of the two components singly the reflex 

 effects in the two limbs are diametrically opposed. 



These results hold over a wide range of intensity of stimuli so long as the 

 intensities of the stimuli right and left are approximately equal. This 

 indicates that the intensity ratio between the ipsilateral and contralateral 

 effects, both of inhibition and excitation, remains but little changed over a 

 wide range of different intensities of stimulation. The absolute values rise 

 and fall with increase and decrease of stimulation, but the relative values 

 remain about the same, subject to two alterations which will be mentioned 

 later. 



The above observations therefore come under the rubric of algebraic 

 summation in double reciprocal innervation. They show that double 

 reciprocal innervation can change reciprocal innervation of symmetrical 

 muscles into identical innervation of them. Double reciprocal innervation* 

 applied to antagonistic muscles does noj; result in identical innervation of 



* 'Roy. Soc. Proc.,' 1909, B, vol. 81, p. 249. 



Fig. 7. — Explanation in text. 



