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.
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.
Slow Muscles Slow Mind
There is abundant scientific proof that the quality and quantity of muscle, brain, and nerve (physical) activity in a particular individual are accompanied by corresponding qualities and quantities of mental activity. That is, when a person's muscle action, nerve response, and brain action are sluggish, his mind also develops a characteristic of slow action. And vice versa.
We say of a certain acquaintance that he has an alert mind. But his "ego," or mental self, could not act quickly and alertly if his brain, the physical instrument of his mind, did not receive and transmit impressions swiftly to his mentality. The brain does not think. It is as purely physical as any other part of the body. It just handles, or transmits in and out, to and from the mind, the various impressions sent in by different sense muscles, and the mental reflexes or impulses sent out by the innumerable mind centers. Your mind works through your brain. Of course, therefore, the quality and quantity of mental work you are capable of doing are limited by the degree of handling-or-transmitting efficiency characteristic of your particular brain structure.
Any interference with the brain quality or quantity of an individual naturally interferes with his normal mental functioning. If a particular part of a man's brain is injured, the associated mind center is harmed likewise and his mental quality is affected in proportion. Should a certain portion of his brain be cut out, the total quantity of his mental powers would be correspondingly reduced. We all know these things about the brain and the mind. But only a few scientists are familiar with many details of the inter-relation of mind and brain and muscles, which should be known to all people who want to make the most of themselves. The salesman of himself needs to understand his "goods" thoroughly; so as we study the selling process that completes the secret of certain success, we dig into practical psychology a little way now in order to stimulate in you a desire for further exploration of that gold mine of opportunities.