356 w. MCDOUGALL : Of the factors of the attention-process enumerated in the first paper of this series three remain for brief consideration, namely, emotional interest, vascular changes and voluntary effort. EMOTIONAL INTEREST. When an object is of such a nature as to arouse emotion its perception involves the excitement of a neural system, a congenital disposition, which propagates its excitement to many organs, especially the visceral organs. The disturb- ances produced in these stimulate the afferent nerves of these organs and so through them send streams of energy back to the brain ; and in virtue of visceral circuits, similar to the motor circuits described in the third paper of this series (vol. xii., p. 485), these afferent streams of energy return in the main to those neural systems from which issued the impulses that evoked them. They thus intensify the excitement of the system, and re-enforce that system in its rivalry with all others enabling it to inhibit them ; hence by this circular activity which tends to be self-maintaining, like that in the motor circuits, the attention-process is intensified and kept playing about the one object or system of objects, and it is followed by all the effects of intense attention. In so far as emotional excitement operates in this way in re-enforcing the attention-process it must be classed with motor adjust- ments as one of the accessory internal conditions. These considerations render intelligible a certain rule which for many years I have observed with success when wishing to fall asleep. The rule is to turn away the attention from any train of ideas in which the idea of the self is likely to be involved, therefore from all familiar places, persons and things. For the rise to consciousness of the idea of self is almost always accompanied or followed by some degree of emotional excitement which suffuses the brain with free energy and so prevents that gradual quiescence of the brain which leads on to sleep. VASCULAR CHANGES. Many authors have regarded vascular changes as playing an important part in the fixation and remission of attention, and for some indeed no other factors seem to have come into view. I attach no importance to vascular changes in this connexion. If we could suppose that neurones were compact cells, that functional groups of neurones were compact groups and that each such group was supplied by a separate arteriole, then we might suppose that changes in the amount of blood
