sense organs.  The extent of movement may vary from the wide-spread tremors that occur when we are frightened by a thunderstorm to the merest flicker of an eye-lash.  But whatever be its extent, movement invariably occurs when we are stimulated by some object.  This has been demonstrated in startling ways in the psychological laboratory, where even so simple a thing as a piece of figured wall-paper has been shown to produce measurable bodily disturbances.  Ordinarily we do not notice these because they are so slight, sometimes being merely twitches of deep-seated muscles or slight enlargements or contractions of arteries which are very responsive to nerve currents.  But no matter how large or how small, we may be sure that movements always occur on the excitation of a sense organ.  This led us to assert in an earlier chapter that the function of the nervous system is to convert incoming sensory currents into outgoing motor currents.

So ingrained is this tendency toward movement that we do not need even a sensory cue to start it off; an idea will do as well.  In other words, the nervous current need not start at a sense organ, but may start in the brain and still produce movement.  This fact is embodied in the law of ideo-motor action (distinguished from sensory-motor action), “every idea in the mind tends to express itself in movement.”  This motor character of ideas is manifested in a most thorough-going way and renders our muscular system a faithful mirror of our thoughts.  We have in the psychological laboratory delicate apparatus which enables us to measure many of these slight movements.  For example, we fasten a recording device to the top of a person’s head, so that his slightest movements will be recorded, then we ask him while standing perfectly still to think of an object at his right side.  After several moments the record shows that he involuntarily leans in the direction of the object about which he is thinking.  We find further illustration of this law when we examine people as they read, for they involuntarily accompany the reading with movements of speech, measurable in the muscles of the throat, the tongue and the lips.  These facts, and many others, constitute good evidence for the statement that ideas seek expression in movement.

The ethical consequences of this are so momentous that we must remark upon them in passing.  We now see the force of the biblical statement, “Not that which entereth into the mouth defileth the man; but that which proceedeth out of the mouth, this defileth the man.”  Think what it means to one’s character that every thought harbored in the mind is bound to come out.  It may not manifest itself at once in overt action, but it affects the motor pathways and either weakens or strengthens connections so that when the opportunity comes, some act will be furthered or hindered.  In view of the proneness to permit base thoughts to enter the mind, human beings might sometimes fear even to think.  A more optimistic idea, however, is that noble thoughts lead to noble acts.  Therefore, keep in your mind the kind of thoughts that you wish to see actualized in your character and the appropriate acts will follow of their own accord.