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



after very weak stimuli. It seems favoured by shortness of duration of the 

 stimulus, e.g., a duration of half a second or a second seems more favourable 

 than one of 4 seconds. It is seen under decerebrate rigidity as well as after 

 spinal transection. The after-contraction in vast o-crur ens or gastrocnemius 

 often does not extend the knee or ankle to as great a degree as existed under 

 the decerebrate rigidity, immediately before the reflex inhibition — the first 

 effect of the stimulus — set in. Sometimes, however, the after-contraction 

 actually exceeds the degree of contraction existent prior to the reflex 

 inhibition (fig. 1). The after-contraction never, in my experience, sets in 

 during the actual application of the stimulus, but follows as a rebound after 

 its cessation. The rebound is evidently reflex, for it often involves the 

 extensors of hip, knee, and ankle together. 



The inference was drawn above that the reaction is central in its 

 mechanism. That is also borne out by the fact that it is met with under 

 direct stimulation of the cross-section of the spinal cord itself. Thus I have 

 met it when faradising, by the unipolar method, the lateral column of the 

 spinal cord at the 10th thoracic level in the dog. The 7th cervical segment 

 had been exsected seven months previously. From three points in the left 

 ventrolateral column flexion of left hip and knee was obtained as a conjoined 

 movement, together with extension of the right knee. There followed 

 regularly, on cessation of the stimulus, a marked after-extension of left hip 

 and knee. This after-extension was immediately cut short on stimulating 

 the previous point again. But the after-extension was frequently increased 

 by stimulating the left dorsal column. The face of the spinal section 

 stimulated was that distal to the transection made at the time to expose the 

 cross area of the cord for direct excitation. 



[Addendum. — In Section VI above, it was pointed out that the muscles 

 reflexly inhibited in the instances of reciprocal innervation given possess 

 certain physiological characters in common. Among these characters, one 

 that was mentioned was their counteracting gravity by tonic contraction in 

 the habitual posture of the body when erect, e.g., in standing. An instance 

 of reflex reciprocal innervation is, however, furnished by the hind limb (cat), 

 in which there occurs inhibitory relaxation of muscles which in some 

 respects can hardly be supposed to have the function of counteracting 

 gravity in the ordinary erect posture, e.g., standing. This instance is well 

 exemplified when the afferent nerve chosen for exciting the reflex is either of 

 the plantar nerves or the musculo-cutaneous branch of the peroneal below 

 the knee. Stimulation of any of these nerves excites reflex contraction of 

 the flexors of hip, knee, and ankle, and reflex inhibition of the extensors of 



