N O T E O N T H J^: A F T h: R - I ) J S C H A R G I- 

 O F R E ¥ L \i X C E X T RES 



H y 



C. S. SÍIER R INGTO X 



The importance of cióse association between histological and functio- 

 nal studies in biology is, I think, in no field of biology better shown than 

 in the nervous system. We can find no more convincing proof of this 

 than in the immense valué to nervous physiology of the splendid histolo- 

 gical investigations made by the genius and indefatigable labours of the 

 great master to whom this volume is dedicated. Preoccupations prevent 

 me from contributing so fully as I would wlsh to these pages devoted to 

 paying honorable tribute to him. But my contribution, though slight 

 and brief, is olTered with none the less sympathy and the wish to add 

 one token more of the world-wide appreciation in which he is held. 



1 lióse who study the reflex actions of the nervous system have to 

 ask many questions to which a full answer is not yet forthcoming, even 

 with the simpler reflexes. One of these questions seems to me the follow, 

 ing. What process in the nervous centre enables the nervous discharge 

 of the centre to outlast the duration of the centripetal impulses arriving 

 in it. It has been commonly observed that the motor discharge from- 

 for instance, the spinal cord, exhibits the so-called after-discharge. The 

 spinal mechanism acts as if it had a momentum like, so to say, the mo- 

 vement of a mass that owing to its inertia when once set in motion does 

 not quickiy come to rest after cessation of the forcé which disturbed it 

 from the resting position. This momentum of action, this continuance 

 of the nervous discharge and therefore of the muscular contraction, must 

 tend to impair the delicacy of the co-ordination when one action has to 

 be quickiy foUowed by another which the earlier would impede. To 

 cure this defect seems to be one of the purposes of reflex inhibition, be- 

 cause we see that in the sequence of different retlcx actions an immediate 



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