nstitute consciousness, result from this. Sensations excite ideas and
emotions; these in their turns arouse other ideas and emotions; and so,
continuously. That is to say, the tension existing in particular nerves,
or groups of nerves, when they yield us certain sensations, ideas, or
emotions, generates an equivalent tension in some other nerves, or
groups of nerves, with which there is a connection: the flow of energy
passing on, the one idea or feeling dies in producing the next.

Thus, then, while we are totally unable to comprehend how the excitement
of certain nerves should generate feeling--while, in the production of
consciousness by physical agents acting on physical structure, we come
to an absolute mystery never to be solved; it is yet quite possible for
us to know by observation what are the successive forms which this
absolute mystery may take. We see that there are three channels along
which nerves in a state of tension may discharge themselves; or rather,
I should say, three classes of channels. They may pass on the excitement
to other nerves that have no direct connections with the bodily members,
and may so cause other feelings and ideas; or they may pass on the
excitement to one or more motor nerves, and so cause muscular
contractions; or they may pass on the excitement to nerves which supply
the viscera, and may so stimulate one or more of these.

For simplicity's sake, I have described these as alternative routes, one
or other of which any current of nerve-force must take; thereby, as it
may be thought, implying that such current will be exclusively confined
to some one of them. But this is by no means the case. Rarely, if ever,
does it happen that a state of nervous tension, present to consciousness
as a feeling, expends itself in one direction only. Very generally it
may be observed to expend itself in two; and it is probable that the
discharge is never absolutely absent from any one of the three. There
is, however, variety in the _proportions_ in which the discharge is
divided among these different channels under different circumstances. In
a man whose fear impels him to run, the mental tension generated is only
in part transformed into a muscular stimulus: there is a surplus which
causes a rapid current of ideas. An agreeable state of feeling produced,
say by praise, is not wholly used up in arousing the succeeding phase of
the feeling, and the new ideas appropriate to it; but a certain portion
ov