98 C. S. Shc-rrington 



action of the second reflex is to suppres the after-discharge of the oppos-. 

 ed earlier reflex. (3n the other hand it may well be that reflex after- 

 discharge signifies a property of nervous centres very useful in reinfor- 

 cing the reaction of the centre to the centripetal impulses which bring 

 the centre into play. 



It is difficult to discover whicli of the morphological elements in the 

 reflex are explains the after-discharge of the reflex action. 'J'he periphe- 

 ral receptor may be partly responsible for it in some cases; but the phe- 

 nomenon is still evident in many cases \\'hen tlie stimulus, e. g. electrical 

 faradisation, is appHed direct to the proximal stump of the cut and bared 

 afferent nerve itself. The discharge of impulses from the centre after ces- 

 sation of the electrical stimulation ot the afterent nerve can in certain 

 cases be at least partly, perhaps wholly, accounted for as follows, if the 

 stimuli are strong. Lucas and Adrián have shoA\n that \\ilh strong 

 electrical stimuli the change produced in the nerve-trunk at the seat 

 of stimulation itself is not a nerve impulse but is a process, "local 

 excitatory change" ^^■hich excites a nerve-impulse. íf the single sti- 

 mulus be strong or violent the "local excitatory change" may last 

 long enough to produce, not merely one impulse per afferent nerve 

 fibre, but two or more in succession per nerve fibre. In this case 

 a single momentary stimulus, e. g. a single induction shock, ap- 

 plied to tlie afferent nerve, causes a short succession of centripetal im- 

 pulses per each nerve-fibre to enter the reflex centre, and there results 

 a brief tetanic discharge from the centre via the motor nerve, producing 

 in its turn a brief tetanic contraction of the muscle. This kind of after- 

 discharge can be termed a pseudo after-discharge because its causation 

 doest not lie primarily in the reflex centre itself. But there seem nume- 

 rous cases where the reflex after-discharge cannot be accounted for by a 

 residuum of stimulation persisting at the seat of stimulation of the affe- 

 ret nerve. For instance after tetanic stimulation of the afferent nerve the 

 reflex contraction provoked in the muscle in some cases persists for a 

 long fraction of a second or more after the cessation of the electric sti- 

 mulation. The contraction dies out during this post-stimatory period 

 gradually, The question arises, by what process in the centre is this par- 

 tial continuance ol discharge produced after the arrival of impulses from 

 the afferent nerve has ceased.^ It might be supposed that such prolonga- 

 tion of the discharge is caused by a super-added reflex originated by the 



