The Disease of the Stiffening of the Arteries. The points at which our pipe-line system is most likely to give way are the valves of the heart, and, more likely still, the muscles of the heart wall and of the walls of the blood vessels. These little muscles are slowly, but steadily, changing all through life, becoming stiffer and less elastic, less alive, in fact, until finally, in old age, they become stiff and rigid, turning into leathery, fibrous tissue, and may even become so soaked with lime salts as to become brittle, so that they may burst under some sudden strain. When this occurs in one of the arteries of the brain, it causes an attack of _apoplexy_, or a "stroke of paralysis." Overstrain, or toxins in the blood, may bring about this stiffening of the arteries too soon, and then, we say that the person is "old before his time." A man is literally "as old as his arteries." The causes which will hasten the stiffening of the arteries are, first of all, prolonged overwork and overstrain,--due especially to long hours of steady work in unwholesome shops or surroundings; second, the presence in the blood of the poisons of the more chronic infectious diseases, like tuberculosis; third, the waste products that are formed in our own body, and are not properly got rid of through lungs, skin, and kidneys; and fourth, the use of alcohol, tobacco, and other narcotics. The Bad Effects of Alcohol. Alcohol is particularly likely to damage the walls of the blood vessels and the heart, first, because it is a direct poison to their cells, when taken in excess, and often in what may appear to be moderate amounts, if long continued; secondly, because it is frequently taken, especially by the poorer, underfed class of workers, as a substitute for food, causing them literally to "spend their money for that which is not bread," and to leave their tissues half-starved; and thirdly, because, by its narcotic effects, it decreases respiration and clogs the kidneys and the skin, thus preventing the waste products from leaving the body. How the Heart Valves may be Injured. The valves of the heart are likely to give way, partly because they are under such constant strain, snapping backward and forward day and night; and partly, because, in order to be thin enough and strong enough for this kind of work, they have become turned, almost entirely, into stringy, half-dead, fibrous tissue, which has neither the vitality nor the resisting power of the live body-stuffs like muscles, gland-cells, and nerves. They are so tough, however, that they seldom give way under ordinary wear and tear, as the leather of a pump valve, or of your shoes, might; but the thing which damages them, nine times out of ten, is the germs or poisons of some infectious disease.