The insect differs from a mere automaton in this, that it is influenced by old, by registered impressions.  In the higher forms of animated life that registration becomes more and more complete, memory becomes more perfect.  There is not any necessary resemblance between an external form and its ganglionic impression, any more than there is between the words of a message delivered in a telegraphic office and the signals which the telegraph may give to the distant station; any more than there is between the letters of a printed page and the acts or scenes they describe, but the letters call up with clearness to the mind of the reader the events and scenes.

An animal without any apparatus for the retention of impressions must be a pure automaton—­it cannot have memory.  From insignificant and uncertain beginnings, such an apparatus is gradually evolved, and, as its development advances, the intellectual capacity increases.  In man, this retention or registration reaches perfection; he guides, himself by past as well as by present impressions; be is influenced by experience; his conduct is determined by reason.

A most important advance is made when the capability is acquired by any animal of imparting a knowledge of the impressions stored up in its own nerve-centres to another of the same kind.  This marks the extension of individual into social life, and indeed is essential thereto.  In the higher insects it is accomplished by antennal contacts, in man by speech.  Humanity, in its earlier, its savage stages, was limited to this:  the knowledge of one person could be transmitted to another by conversation.  The acts and thoughts of one generation could be imparted to another, and influence its acts and thoughts.

But tradition has its limit.  The faculty of speech makes society possible—­nothing more.

Not without interest do we remark the progress of development of this function.  The invention of the art of writing gave extension and durability to the registration or record of impressions.  These, which had hitherto been stored up in the brain of one man, might now be imparted to the whole human race, and be made to endure forever.  Civilization became possible—­for civilization cannot exist without writing, or the means of record in some shape.

From this psychological point of view we perceive the real significance of the invention of printing—­a development of writing which, by increasing the rapidity of the diffusion of ideas, and insuring their permanence, tends to promote civilization and to unify the human race.

In the foregoing paragraphs, relating to nervous impressions, their registry, and the consequences, that spring from them, I have given an abstract of views presented in my work on “Human Physiology,” published in 1856, and may, therefore, refer the reader to the chapter on “Inverse Vision, or Cerebral Sight;” to Chapter XIV., Book I.; and to Chapter VIII., Book ii.; of that work, for other particulars.