The larger arteries such as the brachials and femorals are most affected. The walls become thinned and show cracks, and areas apparently, but not actually denuded of intima. Yellowish-white, irregular, raised plaques are scattered here and there. Interspersed among these areas are irregularly shaped clean-cut ulcers having as a rule a smooth base, and frequently on the base is a thin plate of calcified matter. The color of these denuded areas is usually brownish red or reddish brown. White thrombi may be deposited on these areas. The danger of an embolus plugging one of the smaller arteries is great and probably happens more often than we think. The collateral circulation is able to supply the thrombosed area. Should the thrombus be on the carotid arteries, hemiplegia may result from cerebral embolism. On microscopic examination of the arteries there is seen extreme degeneration of all the coats, the degeneration of the media leading almost to an obliteration of that coat. On seeing such arteries as these one wonders how the circulation could have been maintained and the organs nourished. Senile atrophy of the internal organs naturally goes hand in hand with such arterial changes. There is, as a rule, no increase in arterial tension; on the contrary, the pressure is apt to be low. This is readily understood when the heart is seen. This organ is small, the muscle is much thinned, it is flabby and of a brownish tint, the so-called "brown atrophy." Microscopically, there is seen to be much fragmentation of the fibers with a marked increase of the brown pigment granules which surround the cell nuclei. Cases are seen, however, in which blood pressure increases as the patient grows older. The hearts in such cases are more or less hypertrophied and show extensive areas of fibroid myocarditis. From what has been said, it follows that hypertension alone may be the cause of arteriosclerosis; that certain poisons in the blood which attack the media and cause it to degenerate and weaken cause arteriosclerosis without increased blood pressure; that the normal blood pressure may be, for the artery which is physiologically weakened in an individual over fifty, really hypertension, and arteriosclerosis may result. Our observations lead us to believe that the process is at bottom one and the same. The different types noted clinically depend upon the nature of the etiologic factors and the kind of arterial tissue with which the individual is endowed. This view at least brings some order out of previous chaos, and corresponds well with our present knowledge of the disease.