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1905.|]° On Reciprocal Innervation of Antagonistic Muscles. 285 

be precluded from acting on a motor neurone at a time when another and 
different reflex is employing it. This is one of the data for what I have 
termed the “principle of the final common path.”* The preclusion of the 
motor neurone from the influence of one reflex does not preclude it 
from the action of other different reflexes, but still leaves it open to 
respond to the action of those other reflexes—that, in fact, appears to be 
one of the services of this inhibition to the organism. This seems to 
indicate that the motor neurone itself is not, in some cases at least, the 
seat of the inhibition, for if so, it would be inhibited for all reflexes ; unless 
the motor neurone is functionally divisible, and one part of it, eg., one set 
of dendrites, can be inhibited at a time when another are not. The seat of 
the inhibition appears, therefore, with some likelihood, to lie neither in the 
afferent neurone proper nor in the efferent neurone proper, but in an inter- 
nuncial mechanism—synapse or neurone—between them. I say “neurone 
proper” because a synapse would include the terminal of one neurone and 
the proximal part of the next. 
The “after-discharge ” 
contraction of muscles, might well be disadvantageous to the organism. That 
it is rapidly arrested by the inhibitory side of a succeeding reflex, is an 
adaptation which facilitates the successive interchange of reflexes. 
of a “centre,” with its concomitant persistence of 
Having in view this active, 2.c., non-passive, character of the initiation of 
change in central state which the inhibition implies, and also our power 
to excite opposed muscles synchronously in certain willed movements, 
I have, in the instances of various afferent nerves and points of 
skin that regularly evoke inhibition of some particular test-muscle, 
tried by varying the kind of stimulation, grading the intensity of the stimuli, 
cooling the nerve, etc., to change their effect from reflex inhibition to 
reflex contraction. Thus, with the knee extensor as test-muscle, I have 
experimented for this purpose on the skin of the leg below the knee, and 
on the hamstring nerve and its branches, the nerve from the inner and 
outer heads of gastrocnemius, the dorsal digital nerves, the anterior tibial 
nerve above the ankle, the interna] saphenous and its branches below the 
knee, the external saphenous, and the plantar digitals. In all cases save 
in one I have been unsuccessful; the result has always remained inhibition, 
save in the single instance of the planta.- From that surface I found that 
certain kinds of innocuous mechanical stimuli—but not other stimuli—elicit 
regularly a reflex contraction of the extensor instead of reflex relaxation. 
* Sherrington, ‘ Brit. Assoc. Reports,’ 1904, loc. cit. 
+ Sherrington, ‘ Roy. Soc. Proc.,’ vol. 66, p. 66, 1899 ; and ‘Journ. of Physiol.,’ vol. 30 
p. 39, 1903. 

