tested by experiment; and before any man has a right to affirm that there
is only one quality of physical force in nature, which, by undergoing
transformation and metamorphosis, shall account for all its phenomena, I
have a right to ask whether the hypothesis, that there may be another,
has been experimentally tested. It would then be time for me to accept
the conclusion that there is only one, and that it is an unfathomable
mystery how this one force should be able to perform all the functions
attributed to it.

_Germsell_. I admit that the forces called vital are correlates of the
forces called physical, if you choose to call that a distinction; but
their character is conditioned by the state of the brain, and it comes to
the same thing in the end. The seat of emotion as well as of thought is
the brain, and it entirely depends on its chemical constitution, on its
circulation, and on other causes affecting that organ, what you think,
and feel, and say, and do. People's characters differ because their
brains do, not because there is any difference in the vital force which
animates them.

_Rollestone_. You might as well say that sounds differ because their
aerial vibrations differ, but those vibrations only differ because the
force makes them differ which is acting upon them. They don't generate
tunes, but convey them. And the result, so far as our hearing is
concerned, depends upon what are called the acoustic conditions under
which the vibrations take place. Just so the brain possesses no
generating function of its own; it deals with and transmits the ideas and
emotions projected upon it according to the organic conditions by which
it may be affected at the time, whether those ideas and emotions are
produced by external stimuli, or apparently, but only apparently, as I
believe, owe their origin to genesis in the brain itself. In the one