of the one by the other is a hidden place of nature which has hitherto been
investigated with little or no success.

h. The impossibility of distinguishing between mind and body. Neither in
thought nor in experience can we separate them. They seem to act together;
yet we feel that we are sometimes under the dominion of the one, sometimes
of the other, and sometimes, both in the common use of language and in
fact, they transform themselves, the one into the good principle, the other
into the evil principle; and then again the 'I' comes in and mediates
between them. It is also difficult to distinguish outward facts from the
ideas of them in the mind, or to separate the external stimulus to a
sensation from the activity of the organ, or this from the invisible
agencies by which it reaches the mind, or any process of sense from its
mental antecedent, or any mental energy from its nervous expression.

i. The fact that mental divisions tend to run into one another, and that
in speaking of the mind we cannot always distinguish differences of kind
from differences of degree; nor have we any measure of the strength and
intensity of our ideas or feelings.

j. Although heredity has been always known to the ancients as well as
ourselves to exercise a considerable influence on human character, yet we
are unable to calculate what proportion this birth-influence bears to
nurture and education. But this is the real question. We cannot pursue
the mind into embryology: we can only trace how, after birth, it begins to
grow. But how much is due to the soil, how much to the original latent
seed, it is impossible to distinguish. And because we are certain that
heredity exercises a considerable, but undefined influence, we must not
increase the wonder by exaggerating it.