If there were one single health habit that I would have inculcated above all others, it would be the habit of regularly evacuating the bowels. While constipation is not the worst ill in the world, it causes much trouble, annoyance and a considerable degree of ill health, and, in my opinion, a considerable degree of unhappiness. A physician may be pardoned for frank advice: all the matters concerning the bowels, such as coarse foods, plenty of water and exercise, are secondary compared to the habit of going to the stool at the same time each day, whether there be desire or not. A child should be trained in this matter as definitely as he is trained to brush his teeth. In fact, I think that the former habit is more important than the latter. The mood of man is remarkably related to the condition of his gastro-intestinal tract and the involuntary muscle of that tract is indirectly under the control of the will through habit formation. Sleep[1] the mysterious, the death in life which we all seek each night, is likewise regulated by habit. Arising from the need of relief from consciousness and bodily exertion, the mechanism of sleep is still not well understood. Is there a toxic influence at work? is the body poisoned by itself, as it were, as has been postulated; is there a toxin of fatigue, or is there a "vaso-motor" reaction, a shift of the blood supply causing a cerebral anaemia and thus creating the "sleepy" feeling? The capacity to sleep is a factor of great importance and we shall deal with it later under a separate heading as part of the mechanism of success and failure. At present we shall simply point out that each person builds up a set of habits regarding sleep,--as to hour, kind of place, warmth, companionship, ventilation and even the side of the body he shall lie on, and that a change in these preliminary matters is often attended by insomnia. Moreover, a change from the habitual in the general conduct of life--a new city or town, a strange bed, a disturbance in the moods and emotions--may upset the sleep capacity. Those in whom excitement persists, or whose emotions are persistent, become easily burdened with the dreaded insomnia. Sleep is dependent on an exclusion of excitement and exciting influences. If, however, exciting influences become habitual they lose their power over the organism and then the individual can sleep on a battle field, in a boiler factory, or almost anywhere. Conversely, many a New Yorker is lulled to sleep by the roar of the great city who, finds that the quiet of the country keeps him awake. [1] As good a book as any on the subject of sleep is Boris Sidis's little monograph.