1907. | Innervation of Antagonistic Muscles. 67 
fore, in a series of reflexes such as that of which fig. 8, A and B, shows the 
extensor muscle’s reactions, the active movements of flexion and extension, 
alternating one with another, do not require alternation of two external 
stimuli, one evoking flexion, the other extension. Such observations 
show that one and the same stimulus, intermittently applied, suffices fully 
for the double phases of the reflex movement. Contraction-phase ensues 
in the muscle antagonistic to the flexor in each pause of application of the 
external stimulus. In other words, a neural discharge, due to successive 
induction, produces after each reflex contraction of the flexor a compensatory 
contraction of the extensor, bringing the limb back to extension and keeping 
it there until renewal of the external stimulus again inhibits the extensor, 
and contracts the flexor. In this case, unlike the “ scratch-reflex,” the 
rapidity of succession of the phases of the cyclic reflex is in the hands of the 
external stimulus. If the rate of intermission of that stimulus is slow, the 
alternation of the phases of the reflex is likewise slow ; if the repetitions of 
the stimulus follow quickly, the cycle of the reflex proceeds quickly. That is 
to say, the rate of stepping of the limb depends on the rate of recurrence of 
the applications of a single uniform stimulus which excites, during each of its 
applications, one phase of the reflex act, and is followed by the other phase. 
Addendum.—December 3, 1907. 
(With HerBerT E. Roar, M.D. Toronto.) 
(Received December 4, 1907.) 
Mention was made in the foregoing* of the possibility that not only 
complete withdrawal of the inhibitory stimulus, but likewise mere lessening 
of its intensity, might induce from the inhibited centre fresh motor discharge 
and consequent contraction of the muscles previously kept relaxed by 
reflex inhibition. This proves to be actually the case. To obtain this effect 
under the experimental condition, the reduction of intensity of the external 
stimulus has had to be considerable, and the reduction has been abrupt. 
The method adopted has been that followed in studying the influence of 
the intensity of the external stimulus on the power of the stimulus to break 
through reflex fatigue The resistance of the primary circuit has-been 
suddenly altered by introduction of further resistance of known amount. 
With the current and inductorium used, no rebound contraction was obtained 
under our conditions of experiment when the resistance was increased by 
less than 30 ohms. Fig. 9 shows the effect of abruptly reducing the current 
* Cf. also ‘ Journ. of Physiology,’ vol. 36, p. 191. 
+t Ibid., vol. 34, p. 42. 
