loo C. S. Sherrington 



Another possibility is that in the reflex centre there exict neurones 

 which maintain and reinforce the excitation of the final moto-neurone, by 

 a sort of circular re-excitation, in a similar manner to the causation of 

 auricular flutter in the heart. T. Lewis has shown from his electrical stu- 

 dies of the heart, that auricular flutter is caused and maintained by the 

 waves of muscular excitation t^king a circular course so as to re-excite 

 rhythmically the fibres along which they have just previously passed. The 

 neurone, Avith its rhythmic function founded on refractory phase and the 

 "all or none" principie (Mareyi so fundamentally resembles in its action 

 — except for contraction — the cardiac muscle fibre, that this comparison 

 is not merely fanciful. We have only to suppose t\vo short neurones in- 

 tercalated, even as a side path, between the primary afferent neurone and 

 the final moto-neurone and if the preterminal neurone sent an axone-col- 

 lateral back to the ante-penultimate, we should have the morphological 

 mechanism required. ür, we may remember that in some instances the 

 axone of the final moto-neurone is seen to give oíT near the pericaryon a 

 short collateral within the spinal grey matter of the reflex centre. 7~his 

 collateral may end in a synapse on a short neurone intercalated between 

 primary añ"erent neurone and final moto-neurone. Such an arrangement 

 could provide a mechanism for prolonging automatically the discharge 

 from the nerve-centre after the stimulation of the primary añ"erent neuro- 

 ne itself had ceased. 



Among the most striking cases of reflex after- discharge are those of 

 «rebound •■ contraction after inhibition. The muscle shows on cessation 

 of the stimulus that has caused reflex relaxation of it a contraction which 

 may be mucli greater than it had been before the inhibitory relaxation oc- 

 curred. There are many torms of rebound contraction and they have 

 been described. Post-stimulation increase of reflex contraction follo\\ing 

 on reflex contraction is also often seen. 



In this case there is reason to suspect that that has been some 

 reflex inliibition algebraically summed with the reflex excitation. The 

 proprioceptive afí"erent nerves of the muscle are not essential for 

 rebound contraction although they are usually a favourable adjunct. 

 Rebound contraction is a tonic phenomenon, and the anatomical con- 

 ditions are more complex than those in which after-discharge in its 

 simpler forms can be studied. It was in regard to these latter that 

 the question at opening of this Note was raised. The hypotheses 



