material to retain
traces or relics of impressions brought to it by the organs of sense;
hence, nervous ganglia, being composed of that material, may be
considered as registering apparatus. They also introduce the element
of time into the action of the nervous mechanism. An impression, which
without them might have forthwith ended in reflex action, is delayed,
and with this duration come all those important effects arising through
the interaction of many impressions, old and new, upon each other.

There is no such thing as a spontaneous, or self-originated, thought.
Every intellectual act is the consequence of some preceding act. It
comes into existence in virtue of something that has gone before. Two
minds constituted precisely alike, and placed under the influence of
precisely the same environment, must give rise to precisely the same
thought. To such sameness of action we allude in the popular expression
"common-sense"--a term full of meaning. In the origination of a
thought there are two distinct conditions: the state of the organism
as dependent on antecedent impressions, and on the existing physical
circumstances.

In the cephalic ganglia of insects are stored up the relics of
impressions that have been made upon the common peripheral nerves, and
in them are kept those which are brought in by the organs of special
sense--the visual, olfactive, auditory. The interaction of these raises
insects above mere mechanical automata, in which the reaction instantly
follows the impression.

In all cases the action of every nerve-centre, no matter what its stage
of development may be, high or low, depends upon an essential chemical
condition--oxidation. Even in man, if the supply of arterial blood
be stopped but for a moment, the nerve-mechanism loses its power; if
diminished, it correspondingly declines; if, on the contrary, it
be increased--as when nitrogen monoxide is breathed--there is more
energetic action. Hence there arises a need of repair, a necessity for
rest and sleep.

Two fundamental ideas are essentially attached to all our perceptions
of external things: they are SPACE and TIME, and for these provision is
made in the nervous mechanism while it is yet in an almost rudimentary
state. The eye is the organ of space, the ear of time; the perceptions
of which by the elaborate mechanism of these structures become
infinitely more precise than would be possible if the sense of touch
alone were resorted to.

There