So far as the anatomical lesions in the aorta and branches are concerned, there is much uniformity even though the etiologic factors have been diverse. The only difference is one of extent. To Thoma we owe the first careful work on arteriosclerosis. He regarded the lesion in arteriosclerosis as one situated primarily in the media; there is a lack of resistance in this coat. His views are now chiefly of historical interest. As the author understands him, he considered a rupture in the media to be the cause of a local widening and consequently the blood could not be distributed evenly to the organ which was supplied by the diseased artery or arteries. Moreover, there was danger of a rupture at the weak spot unless this were strengthened. It was essential for the even distribution of blood that the lumen be restored to its former size. Nature's method of repair was a hypertrophy of the subintimal connective tissue and the formation of a nodule at that point. The thickening was compensatory, resulting in the establishment of the normal caliber of the vessel. Thoma showed that by injecting an aorta in the subject of such changes, with paraffin at a pressure of 160 mm. of mercury, these projections disappeared and the muscle bulged externally. He recognized the fact that the character of the artery changed as the years passed, and to this form he gave the name, primary arteriosclerosis. To the group of cases caused by various poisonous agents, or following high peripheral resistance and consequent high pressure, he gave the name, secondary arteriosclerosis. This is a useful but not essential division, as the changes which age and high tension produce may not be different from those produced in much younger persons by some circulating poison. And most important to bear in mind, octogenarians may have soft, elastic arteries. As the body ages, certain changes usually take place in the arteries leading to thickening and inelasticity of their walls. This is a normal change, and in estimating the palpable thickening of an artery, such as the radial, the age of the individual must always be considered.