276 Prof. C. 8. Sherrington. [Apr. 17, 
and in the reflex exhibited as contraction in the knee flexors of the other limb, 
good agreement is found; the number has been. often actually the same, 
though the observations are made alternately first one on one limb, then one 
on the other limb. Figs.14 and 1B,and 24 and 28 are such pairs, and illustrate 
the kind of agreement. | 
(0) The course of the “ flexion reflex” as shown in myograms differs much 
from that of certain other reflexes of the limb, notably from the “extensor 
thrust” and from the “scratch reflex.” Its duration broadly speaking follows 
more closely than that of those reflexes the duration of the eliciting stimulus. 
If the stimulus is quite brief and not intense the myogram shows but a short 
continuance of the development of the effect after the external stimulus itself 
has ceased. I have instances of this which appear not fully explicable by 
inertia of recording apparatus. The after-effect is longer when the stimulus 
is more intense. In both respects the reflex inhibition approximates to 
the reflex contraction. The “flexion reflex” by adjustment of the intensity 
of the stimulus can be graded as to its amplitude. This grading is seen not 
only as a grading of the amplitude of contraction of the flexors when the 
stimulus is applied to the limb with intact knee flexors, but as a grading of 
the amplitude of relaxation when the stimulus is applied to the limb with 
intact knee extensors. 
These correspondences support the view that the reflex inhibition 
(relaxation) and the reflex excitation (contraction) are part and parcel of one 
and the same reflex reaction; and that although opposite in direction they 
are co-ordinate reciprocal factors in one united response. | 
II. It was previously shown that stimulation of the afferent nerve of the 
flexor muscles of the knee inhibits the knee jerk elicitable from the extensor 
muscle of that joint ;* and that it inhibits the tonus of that muscle.t In the 
case of certain other muscular combinations it was further shown that the 
reaction which throws one set of muscles into active contraction can inhibit 
not only the tonus of the antagonistic set but also can cut short their active 
contraction.t I find this inhibition of an active reflex contraction in the 
antagonistic muscles is also demonstrable as a spinal reflex with the muscles 
at the knee joint. It can be studied by stimulating the central end of the 
hamstring nerve during the production of a “crossed extension reflex” 
elicited by appropriate stimulation of the opposite leg (figs. 38 and 4); or by 
stimulating under similar circumstances, namely during production of the 
* © Roy. Soc. Proc.,’ vol. 52, 1893. 
+ Ibid., vol. 60, 1896. 
{ ‘Journ. of Physiol.” vol. 17, 1894; ‘Proc. Physiol. Soc.,’ March, 1904, Address to 
Section I, Brit. Assoc., 1904. 
