It is only necessary to call attention to the part that alcohol, syphilis and insanity play in heredity. These have been discussed fully in the earlier part of this book. We live rapidly, burning the candle at both ends. It is not strange that so many comparatively young men and women grow old prematurely. While heredity is a factor as far as the prophylaxis of arteriosclerosis is concerned, of far more importance is the mode of life of the individual. Scarcely any of us lead strictly temperate lives. If we do not abuse our bodies by excessive eating and drinking and so wear out our splanchnic vessels and cause general sclerosis by the high tension thereby induced, we abuse our bodies by excessive brain work and worry with all their multitudinous evils. The prophylaxis of arteriosclerosis might well be labeled, "The plea for a more rational mode of life." Moderation in all things is the keynote to health, and to grow old gracefully is an art that admits of cultivation. Excesses of any kind, be they mental, moral, or physical, tend to wear out the organism. People habitually eat too much; many drink too much. They throw into the vascular system excessive fluid combined frequently with toxic products that cause eventually a condition of high arterial tension. It has been shown how poisonous substances absorbed from the intestines have some influence on the blood pressure. Anything that causes constant increase of pressure should be studiously avoided. Mild exercise is an essential feature of prophylaxis. One may, by judicious exercise and diet, make of himself a powerful muscular man without, at the same time, raising his average blood pressure. The man who goes to excess and continually overburdens his heart, will suffer the consequences, for the bill with compound interest will be charged against him. It is a great mistake for any one to work incessantly with no physical relaxation of any kind, and yet, after all, it is not so much physical relaxation that is necessary, as the pursuit of something entirely different, so that the mind may be carried into channels other than the accustomed routes. Diversification of interests is as a rule restful. That is what every man who reaches adult life should aim at. Hobbies are sometimes the salvation of men. They may be ridden hard, but even then they are helpful in bearing one completely away from daily cares and worries. The man who can keep the balance between his mental and physical work is the man who will, other things being equal, live the longest and enjoy the best health. Nowadays the trend of medicine is toward prophylaxis. We give the state authority to control epidemics so far as it is possible by modern measures to control them.