We know that a deficiency or lack of thyroid secretion will inhibit sexual emotion and conception, will produce stupidity and inertia; will diminish vitality. On the other hand, excessive thyroid secretion drives the entire mechanism at top speed; the emotions are intensified; the skin becomes soft and moist, the eyes are brilliant and staring; the limbs tremble; the heart pounds loudly and its pulsations often are visible; the respiration is rapid; the stimulation of the fear mechanism causes the eyes to protrude (Fig. 16); the temperature mounts at every slight provoca-tion and may reach the incredible height of 110'0 even. In time, the entire organism is destroyed-- literally consumed--by the concentration of dynamic energy. It is interesting to note that in these patients emotion gains complete possession of the final common path; they are wild and delirious-- but they never have pain. All the diseases caused by excessive motor activity may be called kinetic diseases. Against the conditions in life which produce them man reacts in various ways. He intro- {illust. caption = FIG. 51.--CROSS-COUNTRY RACE. Winner of six-mile cross-country race showing typical expression of exhaustion. (Copyright by Underwood and Underwood, N. Y.) duces restful variety into his life by hunting and fishing; by playing golf and tennis; by horseback riding; by cultivating hobbies which effectually. turn the current of his thoughts{illust. caption = FIG. 52.--{A B and C} from the consuming stress and strain of his business or professional life. These diversions are all rational attempts to relieve tension by self-preservative reactions. For the same reason man attempts to relieve the strain of contention with his fellow-man by unions, trusts, corporations. In spite of all efforts, however, many constitutions are still broken daily in the fierce conflicts of competition. We know how often the overdriven individual endeavors to minimize the activities of his motor mechanism by the use of agents which diminish brain activity, such as alcohol, tobacco, and various narcotics. Occasionally also, some person, who can find no respite from his own relentless energies, seeks relief in oblivion by suicide.