As had been stated before, all acts of the living body are reactions. Every movement of our bodies, either voluntary or involuntary, is a reaction--the result of shock or stimulation--and is aroused by an external cause. Voluntary movements are directed from the mind--the mind wills the movement. Voluntary movements may become so automatic that it is difficult to distinguish them from involuntary movements. For example, the players on musical instruments seem to perform without thought. They read music, and their fingers find the notes on the instruments without hesitation and without a mistake--and that, too, so rapidly that it does not appear to be possible that the acts can be the results of mental deliberations.

The same may be said of reading. The person of educated mind will take up a book in which its author sets forth new and novel ideas regarding an old subject, or perhaps presents new ideas, or ideas contrary to those of convention; and almost instantly, without apparent time for analytical thought, the author's premise is interpreted and compared with the fundamentals of knowledge, and the book and its author are placed where they belong. False or true, the reasons for either are forthcoming and final.

The mind becomes so familiar with the foundation of knowledge that it detects an error on sight; yet it does reason, but with lightning-like rapidity, or, what is more true, with the rapidity of thought.

Every act (and thought is an act) is a reaction from an external stimulation. The effects of stimulation are of two kinds. In some the full reaction may take place at the point of stimulation; others, more complex, cause multiple reflex actions. The impulses are sent to the center from the surface terminals by the centripetal (afferent) nerves, and the irritations are reflexly sent from the center over the centrifugal, or efferent, nerves.

The afferent nerves are the nerves of general sensation; also of special and visceral sensibility. impulses of an irritating character imparted to those nerves result in changes of a psychic, sensory, motor, vasomotor, secretory, or trophic character.

Psychic changes may be produced by fear, anger, happiness, etc. Fear may be caused by a telegram conveying bad news; anger, by anything capable of producing anger.

Sensory changes may take place. For example, if ice cream is eaten too rapidly and the stomach is chilled too suddenly, intense pain or severe frontal headache may result, which will pass off as soon as the nerves of the stomach are relieved from the irritation of cold. Headaches are often the result of indigestion, constipation, etc.

Motor changes take place when toxic or other stimulation has become habitual, until tabes dorsalis or other forms of degeneration manifest themselves.

Vasomotor changes occur when alcoholics, tobacco, coffee, or other chemical toxins are used over a long period of time; or when constipation of long standing has caused systemic infection by forcing absorption of the toxins of putrefaction. Sclerosis, or hardening of the arteries, is a vasomotor change.

Secretory changes are produced by many forms of irritation. Pronounced pain, anger, or fear inhibits secretion, stops digestion, and causes poisoning by modifying the fluids of the body. Pleasant thoughts, renewed hope, or success revive secretions and excretions, and transform the invalid into full health.

Trophic or nutritional changes are caused by any and all influences that irritate, depress, or pervert the nervous system. Any influence that puts the mind at rest will improve digestion, establish secretions and excretions, and transform the invalid into health. Those who have cultivated a fear or worry habit must be cured of the habit, after which they may continue in health.

An irritation may spend its force locally, as an escharotic (caustic) may cause an ulcer without awakening reflexes. The sun may burn the skin brown without causing a reflex irritation.

A poised mind may be abused--subjected to abuse that is looked upon as insulting--without having its equilibrium disturbed.

A local irritant may cause a sensation at the nerve center, which stimulates a motor impulse, and the part injured will instantly be removed from the point of irritation.

An irritation may cause a multiple of reflexes. A fright may cause vomiting and purging, a chill, headache, heart palpitation, and other vasomotor changes, as well as perspiration. An injury may cause many--or, if severe, only a few--reflexes.

A simple reflex is produced where the impulse from the point of irritation passes to the nerve center and back, or passes to a multiple of points.

Stimulants which act as builders of disease must be continual. For instance, tobacco, when first used, causes great prostration and vomiting. The nicotine is absorbed in the mouth; it enters the circulation and is distributed to an parts of the body. If the boy or man, at his first experience, were no larger than a cat or a kitten, the amount of nicotine required to prostrate him temporarily would be sufficient to kill him. His size is what saves him. The fact that the boy does not die is no proof that nicotine is not a rank poison.