You know you have distinct sets of muscles which all together make up your composite body.  Perhaps, however, you have not realized before that your mind is not a unit, but is made up of innumerable distinct “mind centers,” each of which functions as independently of the others as your set of eye muscles operates independently of the set of muscles governing the movements of one of your fingers.  And possibly you do not know that each mind center has a distinct brain center, which functions for that particular part alone of your whole mind. Each associated mind-and-brain center also has direct, distinct nerve connections with only one set of muscles.

In fact, you are “a many-minded, many-bodied” man—­a collection of mental and physical parts, a composite man rather than a man unit.  These several parts are in large measure practically independent of one another.  One set of body parts “belongs to” only its particular associated set of mind parts, or mind center.

[Sidenote:  Independent Mind and Body Centers]

If you were constituted otherwise, your life would be very precarious; for the injury or destruction of even a minor part of your body would be fatal to the whole unit.  As it is, you can lose a finger without affecting your eye-sight in the least.  So you might suffer a localized brain injury that would completely paralyze a finger, without impairing your sight at all.  Either the mind center that governs a finger, or the set of muscles in that finger can be affected without necessarily reacting upon any other mind center or any other set of muscles.

[Sidenote:  Interrelation Of the Ego And Physical Man]

But if the mind center that governs a certain set of muscles is affected, that set of muscles also is directly affected and at once.  Likewise if anything happens to a particular set of muscles, the reaction is instantly transmitted to its associated mind center through the “direct wire” nerves and brain center which particularly serve that part of the mind.

Great scientists have studied mental and physical phenomena in inter-relation and have learned certain facts.  For example, it is known that “the mind” not only affects the general functions of “the body,” but also the rate of bodily activity and the chemistry of body tissues.  Long-continued hard thinking actually does “wear a man out.”  It consumes blood and brain tissue.  It “slows him up.”  It may impair his digestion and appetite.  We all know these things, but the scientists know just why we feel physically tired after using only our minds.

They have learned also that every activity of the mind has a direct effect on the brain substance. That is, each mind operation through the brain changes its physical structure in some degree.  Mental effort or relaxation increases or decreases the amount of blood in the brain.  When you have been using your mind very hard, your head “feels heavy,” and it is unusually heavy then on account of the extra amount of blood weight.  Even the temperature of the brain, particularly of that portion of the brain which is especially functioning at a given moment, is changed with every mental effort.