1907. | Innervation of Antagonistic Muscles. 69 
additional 40 ohms from the primary circuit, the more intense faradic stimulus 
is recontinued. The strong inhibitory relaxation of the extensor muscle at 
once returns. Finally, on discontinuing this, there occurs once more a 
rebound contraction of the extensor muscle, and this rebound is more intense 
still. Such observations show that the central rebound from inhibition to 
super-activity on the part of the reflex arc of the extensor takes place in the 
face of a weak inhibitory stimulus applied to the arc at the time of the 
rebound. 7 
The result seems to have bearings of some theoretical importance. Of 
these one appears as follows. When reflex contraction has proceeded, even 
for a short while, under the application of a full exciting stimulus a weak 
excitatory stimulus, which prior to the strong reaction was able to excite 
the reflex contraction though weakly, loses some of its efficacy and becomes 
less able to provoke its reflex; in other words, tends to fall below the 
threshold value and may become subliminal.* Such a change in excitatory 
reflexes is ascribed to, or rather described under, fatigue effects. In the 
case of the inhibitory reflex just mentioned, an inhibitory stimulus which, 
prior to the action of a stronger inhibitory, was able to produce reflex 
inhibition, fails to do so when repeated after the stronger stimulus has been 
producing inhibition for a short time. If in the case of reflex excitation, 
causing contraction, the phenomenon is permitted to rank as fatigue, the 
similar result observed in reflex inhibition indicates that a similar wearing 
out or blunting of inhibitory effect occurs, and can, under like terminology, 
be called fatigue. There is thus emphasised one more of several significant 
likenesses between the converse processes of reflex excitation and reflex 
inhibition. 
Another bearing of theoretical importance which the observation allows is 
the following. The flexion reflex is in reality the reflex stepping of the 
limb, and such stepping is a rhythmic alternating reflex. The observations 
in the present Note indicate that instead of having to look for two different 
alternately-acting stimuli wherewith to explain the two successive phases of 
flexion and extension characterising the reflex, one stimulus (namely, that 
exciting flexion) is all that may be needed. But that stimulus has to 
be intermittently applied, extension by rebound contraction occurring in the 
intermissions of its application. The additional observations in this 
addendum show that it is not necessary for the stimulus to be actually 
intermittent; it will suffice if it merely suffer periodic decrements of 
intensity—provided the decrements exceed a certain amount. In other 
* Good instances are seen with the scratch-reflex, cf. ‘Journ. of Physiology,’ vol. 34, 
p. 1. 
