With the increased complexity of our modern life comes increased wear and tear on the human organism. "A man is as old as his arteries" is an old dictum, and, like many proverbs, the application to mankind today is, if anything, more pertinent than it was when the saying was first uttered. Notwithstanding the fact that the average age of mankind at death has been materially lengthened--the increase in years amounting to fourteen in the past one hundred years of history--clinicians and pathologists are agreed that the arterial degeneration known as arteriosclerosis is present to an alarming extent in persons over forty years of age. Figures in all vital statistics have shown us that all affections of the circulatory and renal systems are definitely on the increase. "Arterial diseases of various kinds, atheroma, aneurysm, etc., caused 15,685 deaths in 1915, or 23.3 per 100,000. This rate, although somewhat lower than the corresponding ones for 1912 and 1913, is higher than that for 1914, and is very much higher than that for 1900, which was 6.1." The great group of cases of which cardiac incompetence, aneurysm, cerebral apoplexy, chronic nephritis, emphysema, and chronic bronchitis are the most frequent and important appear as terminal events in which arteriosclerosis has probably played an important part. Thus, in the sense in which we speak of tuberculosis or pneumonia as a distinct disease, we can not so designate the diseased condition of the arteries. Arteriosclerosis is not a disease =sui generis=. It is best viewed as a degeneration of the coats of the arteries, both large and small resulting in several different more or less distinct types. These types blend one into the other and in the same patient all types may be found. Thus the sclerosis of the arteries is the result of a variety of causes, none of which is definitely known in the sense of a bacterial disease. As we shall see later, one type of arteriosclerosis has a special pathology and etiology, the syphilitic arterial changes.