TRANSACTIONS OF SECTION I. 739 
of a funnel to its narrow egress. The simile is bettered by supposing that 
within the general systemic funnel the conducting paths of each receptor may 
be represented as a funnel inverted, so that its wider end is more or less co- 
extensive with the whole plane of emergence of the final common paths. All 
these private paths converge in the nervous system to the great central organ, 
the spinal cord and brain, whence on the other hand all the final common paths 
irradiate. This central organ is, to return to our earlier metaphor, a vast network 
whose lines follow a certain pattern. But, as we see from the instances cited— 
more could be given abundantly, had we time—the pattern is unstable, the details 
of connection shift from moment to moment. We might compare the central 
organ with a telephone exchange, where from moment to moment the connections 
between starting and end points are changed to suit passing requirements. In 
order to realise the exchange at work, one has to add to its purely spatial plan the 
temporal datum that within certain limits the connections of the lines shift to and 
fro. The connections of any entrant path not only offer different degrees of resistance, 
but their resistances, both absolutely and relatively, vary from occasion to occasion. 
It is not merely that general conditions of nutrition, of blood-supply, &c., affect 
these resistances. The functional conductive activity of the nervous organ itself 
produces from moment to moment the temporary opening of some connections and 
the temporary closing of others. A good example is the ‘reciprocal innervation ’ 
of antagonistic muscles—when one muscle of the antagonistic couple is thrown into 
action the other is thrown out of action. This is only a widely spread special case 
of a general principle. The general principle is the mutual interaction of arcs 
which embouch upon one and the same common path. Unlike arcs have successive 
use, but not simultaneous use of the common path. Like arcs mutually reinforce 
each other in their action on the common path, Expressed teleologically, the 
common path, although economically subservient for various purposes, is yet used 
only for one purpose at a time. 
Thus the reaction initiated by one receptor while in progress excludes in 
various directions the reactions of other receptors. In this way the motor paths 
at any moment accord in a united pattern for harmonious synergy, co-operating 
for one effect. In the case of simple antagonistic muscles, and in the instances 
of simple spinal reflex arcs, the shifts of pattern of the conductive network 
from occasion to occasion are but of small extent. The co-ordination covers 
one limb or a pair of limbs. But the same principle extended to the reac- 
tions of the great arcs arising in the projicient receptor organs of the head, 
e.g. the eye, that deal with wide tracts of musculature as a whole, involves much 
further-reaching shift of the conductive pattern. The singleness of action from 
moment to moment thus assured is a keystone in the construction of the indi- 
vidual whose unity it is the specific office of the nervous system to perfect. 
Releasing forces acting cn the brain from moment to moment shut out from 
activity whole regions of the nervous system, as they conversely call vast other 
regions into play. The interference of unlike arcs and the reinforcement of like 
ares seem to lie at the very root of the great psychical process of ‘attention.’ I 
will not trench on psychological ral es of the problem. 
I have urged that the struggle between dissimilar arcs for mastery over their 
final common path takes place in the synaptic field at origin of the final neurones. 
Mutual reinforcement by similar arcs seems also referable to the same synaptic 
field. As to the nature of the physiological processes involved, little, it appears to 
me, can be said, The final common path seems an instrument more or less passive 
in the hands of the various arcs that use it. Thus in the scratch reflex one are can 
impress one rhythm on it, another another. And in ‘fatigue’ Fc reveals, though it 
does not share, the failure of force of the tired are playing onit. In regard to the 
reciprocal innervation of antagonistic muscles W. MacDougall has offered a sug- 
estion of great interest, for which he obtains support from various sensual reactions, 
e suggests that the neurones of an antagonistic pair are so coupled that when one 
becomes active it drains energy from its fellow. This takes cognisance of the 
significant fact that central inhibition seems always accompanied by heightened 
activity at some related spot. Yet at certain times both the antagonists can 
3B2 
