From these premises it would appear that under the influence of fear, most, perhaps all, of the organs of the body are divided sharply into two classes: First, those that are stimulated, and, second, those that are inhibited. Those that are stimulated are the entire muscular system, the vasomotor and locomotor systems, the senses of perception, the respiration, the mechanism for erecting the hair, the sweat-glands, the thyroid gland, the adrenal gland (Cannon), and the special senses. On the other hand, all the digestive and procreative functions are inhibited. What is the significance of this stimulation of some and inhibition of other organs? As far as we know, the stimulated organs increase the efficiency of the animal for fight or for flight. It is through skeletal muscles that the physical attack or escape is effected; these muscles alone energize the claws, the teeth, the hoofs, and the means for flight. The increased action of the muscles of the heart and the blood-vessels increases the efficiency of the circulation; the secretion of the adrenal gland causes a rise in the blood-pressure; the increased action of the thyroid gland causes an increased metabolic activity; there is evidence that glycogen is actively called out, this being the most immediately available substance for the production of energy; the increased activity of the respiration is needed to supply the greater need of oxygen and the elimination of the increased amount of waste products; the dilatation of the nostrils affords a freer intake of air; the increased activity of the sweat-glands is needed to regulate the temperature of the body which the increased metabolism causes to rise. The activity of all the organs of perception--sight, hearing, smell-- is increased in order that the danger may be more accurately perceived. It cannot be a mere coincidence that the organs and the tissues that are stimulated in the emotion of fear are precisely those that are actually utilized in a physical struggle for self-preservation. Are any other organs stimulated by fear except those that can or that do assist in making a defensive struggle? I know of none. On the other hand, if an animal could dispense with his bulky digestive organs, whose functions are suspended by fear, if he could, so to speak, clear his decks for battle, it would be to his advantage. Although the marvelous versatility of natural selection apparently could devise no means of affording this advantage, it nevertheless shut off the nervous current and saved the vital force which is ordinarily consumed by these non-combatants in the performance of their functions. Whatever may be the origin of fear, its phenomena are due to a stimulation of all the organs and tissues that add to the efficiency of the physical struggle for self-preservation and an inhibition of the func-