338 Prof. C. S. Sherrington. On Reciprocal [Mar. 9, 



But if the conditions of experiment provide a pre-existent reflex contraction 

 in the gastrocnemius, relaxation of it is seen to occur. A pre-existent reflex 

 contraction of the gastrocnemius can be provided in several ways. I have 

 for the purpose generally employed stimulation of the central end of the 

 external plantar nerve of the opposite leg, e.g., right. A light weight is 

 attached to the left foot in such a way that the gastrocnemius acts against 

 the weight in maintaining extension at the ankle. On stimulating the 

 proximal end of the above-mentioned cutaneous branch of the left peroneal 

 nerve, the ankle then flexes (fig. 1). The gastrocnemius being the only 

 muscle of the leg whose innervation remains, this flexion must indicate 

 reflex relaxation of that muscle. The requisite precurrent reflex contraction 

 of the gastrocnemius may also be obtained by inducing decerebrate rigidity. 



Myograph 



Signal 

 Signal 



Fig. 1. — Myograph tracing from isolated right gastrocnemius (spinal cat). Upward 

 movement of the recording lever registered contraction of the muscle, downward 

 movement registered relaxation. The upper of the two signals below the myograph 

 line marked the moment and duration of mechanical stimulation applied to central 

 end of a cutaneous branch of the musculo-cutaneous division of left peroneal nerve. 

 This stimulation caused reflex contraction of right gastrocnemius. The lower signal 

 marked the times of application of weak faradism to central end of the similar 

 cutaneous nerve of the right limb. In the right limb all other branches of the 

 peroneal nerve, and all the branches of the popliteal except that to the gastrocnemius, 

 had been severed, as well as obturator, anterior crural, and hamstring nerves, and the 

 insertions of iliopsoas and psoas parvus, and the origins of adductor and pectineus 

 muscles. The inhibitory relaxation of gastrocnemius is seen to be followed on 

 cessation of the stimulation by marked after-rebound to contraction, especially after 

 the second and third repetitions of the inhibitory stimulus. Time is marked above 

 in fifths of seconds. 



One of the features of that rigidity is tonic extension of the ankle joint. 

 Under this condition the reflex which produces contraction of the pretibial 

 flexors of the ankle produces also, simultaneously, a relaxation of the 

 gastrocnemius. 



