734 REPORT—1904. 
other leg scratches, but not the two together. The one reflex that takes place 
prevents the occurrence of the other. The reason is, that although the scratch 
reflex appears unilateral it is not strictly so. Suppose the left shoulder 
stimulated. The left leg then scratches. If the right leg is then examined it 
is found to present slight, steady extension with some abduction. This exten- 
sion of the leg which accompanies the scratching movement of the opposite 
leg contributes to support the animal on three legs while it scratches with the 
fourth. 
Suppose stimulation at the left shoulder evoking the scratching movement of 
the left leg, and the right shoulder then appropriately and strongly stimulated. 
This latter stimulus often inhibits the scratching movement in the opposite leg 
and starts it in its own. In other words, the stimulus at the right shoulder not 
only sets the flexor muscles of the leg of its own side into scratching action, but it 
inhibits the flexor muscles of the opposite leg. It throws into contraction the 
extensor muscles of that leg. In the previous example there was a similar co- 
ordination. The motor nerve to the flexor muscle is therefore under the control 
not only of the arcs of the scratch reflex from the homonymous shoulder, but of 
those from the crossed shoulder as well. But in regard to their influence upon this 
final common path, the arcs from the homonymous shoulder and the opposite 
shoulder are opposed. The influence of the latter depresses or suppresses activity 
in the common path. 
Experiments by Verworn disallow any view that this kind of depression has 
its field in the motor nerve itself. Many circumstances connect it with the place 
where the converging neurones come together in the grey matter at commence- 
ment of the common path. The field of competition between the rival arcs seems 
to lie in the grey matter, where they impinge together upon the final or motor 
neurone. That is equivalent to saying that the essential seat of the phenomenon 
is the synapse between the motor neurone and the axone-terminals of the penulti- 
mate neurones that converge upon it. There some of these arcs drive the final 
path into one kind of action, others drive it into a different kind of action, and 
others again preclude it from being activated by the rest. 
My diagram (fig. 1, B) treats the final common path as if it consisted of a 
single individual neurone. It is, of course, not so. ‘The single neurone of the 
diagram stands for several thousands. It may be objected that in the various 
given actions these motor neurones are implicated in particular sets—one set in 
one action, one set in another. That view seems unlikely. In the scratch reflex, I 
think we canexcludeit. Therhythm of that reflex has the same frequence whether 
it be excited strongly or feebly: thus, whether the extent of the contractions be 
great or small they recur with practically the same frequence. That a muscle con- 
tracts feebly under feeble stimulation of its nerve may be due in some cases 
to a fraction only of the nerve-fibres and muscle-fibres of the preparation being 
then active. But in the scratch reflex the whole group of motor neurones seem to 
act, even when the grade of contraction exhibited is quite weak. Let the 
reflex be excited by stimulation of the skin-point, sa (fig. 1 B), and let the stimulus 
be weak, producing only a feeble reflex. Then let another skin-point, 58 (fig. 1 B), 
be stimulated while sa is being stimulated, and let the stimuli at s8 be timed so 
as to fall alternately with those applied at sa. Then if the two paths impinge on 
two different sets of units in the compound group of motor neurones, evidence of 
two rhythms should appear, for the muscle-fibres can respond to a much quicker 
rhythm than the four per second. But in result the rhythm remains unquickened 
and unaltered. Hither sa prevents the access of s8 to the motor neurones of FC, or 
Sa’s reflex having impressed its own tempo on the neurones of Fo, the stimuli from 
8 fall within a refractory period of the neuronic apparatus. On either supposition, 
sa and s8 must play upon the same individual neurones of the final path. A 
like result is given by all other points I have tried in the receptive field of the 
scratch reflex. Again, in the inhibitions previously mentioned, when there occurs 
the tonic contraction or the relaxation of the flexor we find no intermittent con- 
traction of the scratch reflex grafted on them, as would be the case were that 
intermittent contraction still involving some part of the whole muscle. These 
