The Mind and the Brain | Page 6

of this system, a peculiar
modification which we are not yet able to define. It is this modification
which follows the course of the nerves and is carried to the central parts
of the system. The speed of the propagation of this nerve modification
has been measured by certain precise experiments in psychometry; the
journey is made slowly, at the rate of 20 to 30 metres per second, and it
is of interest that this rate of speed lets us know at what moment and,
consequently, by what organic excitement, the phenomenon of
consciousness is produced. This happens when the cerebral centres are
affected; the phenomenon of consciousness is therefore posterior to the
fact of the physical excitement.
I believe it has required a long series of accepted observations for us to
have arrived at this idea, now so natural in appearance, that the
modifications produced within our nervous system are the only states
of which we can have a direct consciousness; and as experimental
demonstration is always limited, there can be no absolute certainty that
things never happen otherwise, that we never go outside ourselves, and
that neither our consciousness nor our nervous influx can exteriorise
itself, shoot beyond our material organs, and travel afar in pursuit of
objects in order to know or to modify them.

* * * * *
Before going further, we must make our terminology more precise. We
have just seen the necessity of drawing a distinction between the
sensations of which we are conscious and the unknown cause which
produces these sensations by acting on our nervous systems. This
exciting cause I have several times termed, in order to be understood,
the external object. But under the name of external object are currently
designated groups of sensations, such as those which make up for us a
chair, a tree, an animal, or any kind of body. I see a dog pass in the
street. I call this dog an external object; but, as this dog is formed, for
me who am looking at it, of my sensations, and as these sensations are
states of my nervous centres, it happens that the term external object
has two meanings. Sometimes it designates our sensations; at another,
the exciting cause of our sensations. To avoid all confusion we will call
this exciting cause, which is unknown to us, the X of matter.
It is, however, not entirely unknown, for we at least know two facts
with regard to it. We know, first, that this X exists, and in the second
place, that its image must not be sought in the sensations it excites in us.
How can we doubt, we say, that it exists? The same external
observation proves to us at once that there exists an object distinct from
our nerves, and that our nerves separate us from it. I insist on this point,
for the reason that some authors, after having unreservedly admitted
that our knowledge is confined to sensations, have subsequently been
hard put to it to demonstrate the reality of the excitant distinct from the
sensations.[6] Of this we need no demonstration, and the testimony of
our senses suffices. We have seen the excitant, and it is like a friend
who should pass before us in disguise so well costumed and made up
that we can attribute to his real self nothing of what we see of him, but
yet we know that it is he.
And, in fact, let us remember what it is that we have argued upon--viz.
on an observation. I look at my hand, and I see an object approaching it
which gives me a sensation of feeling. I at first say that this object is an
excitant. It is pointed out to me that I am in error. This object, which
appears to me outside my nervous system, is composed, I am told, of

sensations. Be it so, I have the right to answer; but if all that I perceive
is sensation, my nervous system itself is a sensation; if it is only that, it
is no longer an intermediary between the excitant and myself, and it is
the fact that we perceive things as they are. For it to be possible to
prove that I perceive, not the object, but that tertium quid which is
sensation, it has to be admitted that the nervous system is a reality
external to sensation and that objects which assume, in relation to it, the
rôle of excitants and of which we perceive the existence, are likewise
realities external to sensation.
This is what is demonstrated by abstract reasoning, and this reasoning
is further supported by a common-sense argument. The outer world
cannot be summarised in a few nervous systems suspended like spiders
in empty space. The existence of a nervous system