TRANSACTIONS OF SECTION I. 739 
various reflexes seem to treat the final common path as a unit. The diagram 
therefore seems justified in representing the common path, Fc, as a unit. 
We have no time to multiply further now the categories of reflexes playing upon 
the final common path, rc. I might cite the deep reflex are which arises in the 
muscles themselves and is answerable for the mild reflex tonus that even in the 
spinal animal maintains the tonic posture of the limb. Or, instead of having taken 
ares that arise in the skin of the foot, we might have taken others arising above 
the knee, and traced a reflex influence different from the arcs arising in the foot, 
but yet playing upon the same final common path; or we might have taken arcs 
from the skin of the tail, that inhibit the reflex ; or from the fore feet, or the ears. 
There is, however, one instance of action upon this final common path, 
FC, which I would quote. Suppose, while the scratch reflex is being elicited from 
a point at the shoulder, a second point, say 10 centimetres distant, but also in the 
dorsal field of skin, is stimulated. The stimulation at this second point favours the 
reaction from the first point. This is well seen when the stimulus at each point is 
of subminimal intensity. The two stimuli, though each unable separately to invoke 
the reflex, do so when applied both together (fig. 4). This is not due to over- 
lapping spread of the feeble currents about the stigmatic poles of the two circuits 
used. Mere cocainisation of either of the two skin-points annuls it. Moreover, 
it occurs when purely mechanical stimuliare used. It isevident that the arcs from 
the two points, e.g. sa and s@ (fig. 1 B), have such a mutual relation that reaction 
of one reinforces reaction of the other, as judged by the effect upon the final common 
path, xc. Such mutual reinforcement is usual between reflexes of identical species 
evoked from one and the same receptive field, e.g. the nociceptive of the foot. 
Not for all the arcs arising in the receptive field of the scratch reflex can, in my 
experience, this mutual reinforcement be demonstrated. There seems a gradual fall 
in reinforcing power as the distance between the receptors of the arcs increases. 
In this connection the following point is noteworthy. The scratch reflex 
carries the foot broadly toward the place of stimulation. In the spinal dog the 
reflex does not succeed in bringing the foot actually to the irritated point, yet 
when the irritation is far forward the foot is carried further forward, and when 
the irritation is far back the foot is carried further back. A scratch reflex evoked 
by a stimulus applied far back and high up in the dorsal skin is therefore not 
wholly like a scratch reflex evoked from far forward and low down. Now, the 
mutual reinforcement between the scratch reflex arcs in their action on the final 
common path, Fc, seems greater the greater the likeness between the reflex 
actions they initiate. The coalition between the reflexes gradually decreases as 
the interval between their receptive points at the skin surface becomes wider. 
Whether coalition fades into mere indifference, or passes over into antagonism, my 
observations as yet do not say. But there are various receptive regions of the 
body surface that do, in the spinal dog, appear indifferent for the scratch reflex. 
Were it not that the nervous system is perforce mutilated in the ‘spinal’ animal, 
the number of these indifferent arcs might be fewer. In presence of the arcs of 
the great projicient receptors and the brain there can be few receptive points in 
the body whose activities are totally indifferent one to another. Correlation of the 
activities of arcs from receptive points widely apart is the crowning contribution of 
the brain toward the nervous integration of the individual. 
In the case before us, then, the final common path—the motor neurone—to the 
hip flexor muscle is played upon by various categories of reflex spinal arcs. Of 
those mentioned, one category (i), the nociceptive from the leg itself, induces 
strong, steady contraction in the muscle. A second (ii), the scalptor or scratching 
from the dorsal skin, induces rhythmic contraction in the muscle. <A third (iii), 
from the deep structures of the limb itself, induces the mild enduring contraction 
known as spinal tonus. A fourth (iv), eg. the nociceptive from the opposite 
foot, depresses the activity of the muscle probably by excluding from it the 
activity of the other arcs which would excite the final path, the motor neurone. 
And there are many more we could trace from various regions of the body ; also, 
pyramidal and other influences from brain for which our final path is likewise 
common. The arcs within one category may reinforce each other’saction on the. 
1904. 3B 
