1907. | Innervation of Antagonistic Muscles. 55 
operation preparatory to that was carried out under deep chloroform 
narcosis. The brain anterior to the transection was removed. After this 
removal the chloroform narcosis was lightened. The “ flexion-reflex,” 
elicited from an afferent nerve or from some appropriate skin-point, is then 
found to be diphasic. The movement of active flexion is followed by 
a movement of active extension. During the active flexion the extensor 
muscles are relaxed by central inhibition; during the active extension the 
extensor muscles contract. 
The contraction of the extensor muscle, ze. the discharge of the 
extensor motoneurones, never in my experience sets in during the actual 
delivery of the external stimulus used to excite the “ flexion-reflex.” So 
long as that stimulus continues the extensors remain inhibited (fig. 1).* 
It is only after withdrawal of that stimulus that the discharge of the 
extensor motoneurones occurs. The commencement of this discharge, judged 
by the muscle’s contraction, follows withdrawal of the external stimulus 
by a time interval longer than that between commencement of external 
stimulus and onset of the inhibitory relaxation of the muscle. In other 
words, the latency of the contraction-phase is longer than that of the 
inhibition-phase (fig. 1, A, and fig. 8, A). 
That the contraction of extensor muscle, 2.¢., discharge of extensor moto- 
neurone, never occurs during the continuance of the external stimulus, 
distinguishes the reaction from a rhythmic reflex such as the “scratch- 
reflex.” In the scratch-reflex the phases of absence of discharge and of 
occurrence of discharge succeed each on the other in the motoneurone, ¢.7., 
of extensor of knee, during unabated continuance of the external stimulus,t 
and with a period of alternation practically independent of the external 
stimulus. In the case of the “ flexion-reflex” of diphasic character, the 
second phase, the phase of discharge of the extensor motoneurone, cannot 
apparently break through the state of inhibition characterising the first phase 
so long as the external stimulus is unremitted. The first phase may be 
termed, if desired, a refractory phase; but if so it is a refractory phase the 
duration of which depends on the external stimulus, whereas the duration of 
the refractory phase of the scratch-reflex is independent of the external 
stimulus. 
* The time-marker records in fifths of seconds throughout all the figures. The signal 
marking excitation is below. All read from left to right. In all the records (figs. 1—9 
inclusive), descent of the myograph line means relaxation of the muscle, and conversely 
its ascent means contraction of the muscle. 
t Sherrington, ‘Journ. of Physiology,’ vol. 29, p. 58, 1903 ; vol. 31, p. xvii ; vol. 34, 
p. 1; ‘ Integrative Action of the Nervous System,’ p. 45. 
