he first time."--"
How then did you know that I had spoken twice?" My friend was
nonplussed, but what had happened was this: on my first speaking the
impulse of the voice had fallen upon his ear and started a nerve-wave
which had struggled up as far as the lower apparatus at the base of the
brain, and, passing through this, had probably even reached the higher
nerve-centres in the surface of the cerebrum, near to which
consciousness resides, but not in sufficient force to arouse
consciousness. When, however, the attention was excited by my second
address, it perceived the first faint impulse which had been registered
upon the protoplasm of the nerve-centres, although unfelt. Probably most
of my readers have had a similar experience. A word spoken, but not
consciously heard, has a moment afterward been detected by an effort as
distinctly conscious as that made by the man who is attempting to
decipher some old faint manuscript. This incident and its explanation
will serve to illustrate the relation which seems to exist between
consciousness and sensation, and also between consciousness and the
general mental actions.

It will perhaps render our thinking more accurate if we attempt to get a
clear idea just here as to what consciousness is and what it is not.
Various definitions of the term have been given, but the simplest and
truest seems to be that it is a knowledge of the present existence of
self, and perhaps also of surrounding objects, although it is
conceivable that a conscious person might be shut off from all contact
with the external world by abolition of the senses. Consciousness is
certainly not what the philosopher and the theologian call the Ego, or
the personality of the individual. A blow on the head puts an end for
the time being to consciousness, but not to the man's personality.
Neither is consciousness the same as the sense of personal identity,
although it is closely connected with it. The conviction of a man that
he is the same person through the manifold changes which occur in him as
the successive years go on is evidently based on consciousness and
memory. This is well illustrated by some very curious cases in which the
sense or knowledge of personal identity has been completely lost. Not
long ago an instance of such complete loss was recorded by Doctor
Hewater (_Hospital Gazette_, November, 1879). The gentleman who was the
subject of this loss found himself standing upon the depot-platform in
Bela