66 Prof. C. 8. Sherrington. On Reciprocal [Nov. 4, 
conditions tending to asphyxia depress the contraction-phase, and, if allowed 
to continue, soon abolish it. 
The possible importance of “successive induction” as a coordinator of 
reflex actions seems obvious. If a reflex A not only temporarily inhibits a 
contraction B antagonistic to it, but also induces in the are of B, as an 
immediately subsequent result, an excitation, we have a process qualified to 
link together simpler reflexes, so as to form from them reflex cycles of action 
such as characterise the reflex play of the limbs in locomotion. In a 
previous Note it was remarked that a difficulty in thus applying the 
experimental results then obtained lay “in the intensity and long duration ” 
of the stimuli which have to be employed to produce the “successive 
induction.”* “Such intensity and duration certainly do not occur in the 
course of the alternating reflexes ’t as they occur naturally. The observa- 
tions brought forward in the present communication remove that difficulty. 
Rebound contraction from “successive induction” is shown to be elicitable 
by stimuli of even momentary duration, eg., a single make or break shock ; 
and still more readily by stimuli lasting even so brief a time as a twentieth 
of a second. The intensity of electric stimuli that evoke it need not be 
more than just perceptible to the tongue. Mechanical stimuli as well as 
electric also readily produce it. 
The experiments afford, I think, convincing proof that in both fore limb and 
hind limb the ordinary “ flexion-reflex,” as expressed by the extensor muscles, 
is a diphasic reaction. The first phase is relaxation due to central inhibition, 
the second phase contraction due to central discharge. The first endures 
throughout the application of the external stimulus, the second immediately 
follows the withdrawal of that stimulus, and is due to a central rebound 
from the state of inhibition to a state of excitation. In the first phase of the 
reflex the extensor muscles abandon the maintenance of a posture, or the 
execution of a movement in which they were engaged; in the second phase 
they restore that posture to the limb, or reinstitute movement in the 
abandoned direction. The series of reflexes of fig. 8, A and B, is a series of 
“steps” executed by the limb under the sole action of a main extensor 
muscle of the knee (vasto-crureus). It has been shownj that in each reflex of 
such a series, the flexors§ contract during the application of the stimulus, that 
is, at and during time of inhibitory relaxation of the extensors.|| There- 
* Sherrington, ‘Roy. Soc. Proc.,’ B, vol. 77, p. 495.° 
+ Ibid. : 
{ Sherrington, ‘ Roy. Soc. Proc.,’ vol. 52, 1893. 
§ For list, see ‘ Roy. Soc. Proc.,’ B, vol, 79, p. 341. 
|| For list, of. cbid., p. 342, 
