284 Prof. C. 8. Sherrington. Apr 
is no place in which to review theories of inhibition advanced by Hering, 
v. Cyon, Gaskell, Lauder Brunton, Meltzer, Verworn, Fano, Macdougall, 
H. E. Hering, and others, who have written with authority on the subject. 
One point, however, impresses the observer in studying the phenomenon as 
seen in these reflexes. The process, although converse in effect to that 
which “excites” through the motor neurone a “contraction-reflex,” yet 
resembles that in time-relations of onset and other ways sufficiently to 
suggest that the induction of the change of state in the “centre,” if active 
in one case, is active—not passive—in the other. The throwing out of 
action seems, at least, as quick as the bringing into action.* H. E. Hering 
and myselft thought, with cortical reactions, the relaxation might commence 
a little sooner than the contraction of the muscles. : 
In the spinal reflexes dealt with here the inhibition in many cases appears 
not equivalent to merely arresting the play of an excited afferent channel 
upon the motor centre. Were that all, the phenomenon should resemble the 
effect of suddenly stopping the stimulation of the afferent nerve causing the 
reflex. What happens is often not like that; the arrest is more rapid. It is 
usual in spinal reflexes for the reflex contraction to endure for a time after 
cessation of the excitation of the receptive surface or afferent channel. This 
continuance of action of the motor neurone, this “ after-discharge,” is often 
marked in spinal reflexes—I have seen it continue for 20 seconds in the 
“flexion reflex.” It seems natural to attribute it not to an after-action of the 
peripheral afferent nerve, but to a continuance of action by mechanisms excited 
by that on its central side. These mechanisms or mechanism may be inter- 
nuncial between afferent channel and motor neurone, or may be the motor 
neurones themselves, or the synapse between any of these links. This “ after- 
discharge,” whatever its seat, can be at once arrested by the inhibition. It 
sometimes returns again if the arresting stimulus be brief. But the fact 
of its arrest shows that the inhibition acts in these cases differently 
from a mere discontinuance of the excitation of the afferent channel. Its 
effect differs from mere cessation of the exciting stimulus. The seat of this 
inhibition seems, therefore, to lhe at the central end of the afferent neurone. 
Observations on the scratch reflext indicate that in that reflex the motor 
neurones of the flexor muscles of the hind limb can be excited to the clonic 
| discharges characteristic of the reflex at a time when the “flexion reflex ” is 
inhibited from employing them. When the scratch reflex is in progress it is 
more difficult to excite a “ flexion reflex,” and vice versd. One reflex seems to 
* V. supra, § 1. 
+ ‘Pfliiger’s Archiv,’ vol. 68, p. 221, 1897. 
t Sherrington, ‘ Brit. Assoc. Reports,’ 1904, loc. cit. 
