to the
detriment of truth that these processes of positive investigation have
been repudiated. If from the construction of the human brain we may
demonstrate the existence of a soul, is not that a gain? for there are
many who are open to arguments of this class on whom speculative
reasoning or a mere dictum falls without any weight. Why should we cast
aside the solid facts presented to us by material objects? In his
communications throughout the universe with us, God ever materializes.
He equally speaks to us through the thousand graceful organic forms
scattered in profusion over the surface of the earth, and through the
motions and appearances presented by the celestial orbs. Our noblest and
clearest conceptions of his attributes have been obtained from these
material things. I am persuaded that the only possible route to truth in
mental philosophy is through a study of the nervous mechanism. The
experience of 2500 years, and the writings of the great metaphysicians
attest, with a melancholy emphasis, the vanity of all other means.

"Whatever may be said by speculative philosophers to the contrary, the
advancement of metaphysics is through the study of physiology. What sort
of a science would optics have been among men who had purposely put out
their own eyes? What would have been the progress of astronomy among
those who disdained to look at the heavens? Yet such is the preposterous
course followed by the so-called philosophers. They have given us
imposing doctrines of the nature and attributes of the mind in absolute
ignorance of its material substratum. [Sidenote: Necessity of the
interpretation of structure.] Of the great authors who have thus
succeeded one another in ephemeral celebrity, how many made themselves
acquainted with the structure of the human brain? Doubtless some had
been so unfortunate as never to see one! Yet that wonderful organ was
the basis of all their speculations. In voluntarily isolating themselves
from every solid fact which might serve to be a landmark to them, they
may be truly said to have sailed upon a shoreless sea from which the fog
never lifts. The only fact they teach us with certainty is, that they
know nothing with certainty. It is the inherent difficulty of their
method that it must lead to unsubstantial results. What is not founded
on a material substratum is necessarily a castle in the air."

[Sidenote: Intellectual relations of man depend on his nervous system.]
Considering t