Rather contrary to what one would expect, there are no new capillaries advancing from the media to the intima in the nodular form of arteriosclerosis, consequently there is no granulation tissue to heal and leave scars. It must be borne in mind that these changes rarely, if ever, are the only ones found throughout the arterial system. Nevertheless, the manifold changes, as will be shown within, appear to be but stages of one primary process. The character of the changes which are known as diffuse arteriosclerosis seems to have, at first sight, little in common with those of the nodular sclerosis. The aorta may or may not have plaques of nodular sclerosis, while the arteries, such as the radial or temporal, may be beaded or pipe stem in hardness. In spite of these far advanced peripheral lesions the aorta may appear smooth but it is markedly dilated, particularly the thoracic portion, it is noticeably thinned even on macroscopic examination, it has elongated as evidenced by its slight tortuosity, and it has lost the greater part of its elasticity. The abdominal aorta is not so extensively affected, although this, too, shows some elongation and slight thinning. This is considered by some pathologists to be the uncomplicated form of the so-called senile arteriosclerosis. It is more of the nature of a degenerative change, it is true, but, as will be shown later, it has its beginnings, at times, in comparatively young persons and its etiology is not simple. This type has been studied most carefully by Moenckeberg, who showed that on the large branches of the aorta there were depressions due to a degeneration of the middle coat. These depressions encircled the vessel to a greater or lesser extent, causing small bulgings at such places and giving to the vessel a beaded appearance. On viewing such an artery held to the light, the sacculated spots are seen to be much thinner than the contiguous normal artery. Associated with such changes in the aorta and large branches is marked sclerosis of the smaller arteries. Intimal fibrosis is common, together with hypertrophy and fibrosis of the middle coat. Not infrequently periarterial thickening is also seen. Calcification of the media is found and is said to be preceded by hypertrophy of the middle coat. Pure cases of this, the so-called Moenckeberg type, are seen but seldom. Most commonly there are nodules and plaques in the aorta and large branches together with thinning and sacculation of other portions of the vessels' walls. While the two processes appear at a glance to be so different from each other, it is possible for them to have a common origin. The initial lesion is in the media but the resulting sclerotic changes depend upon the kind of vessel, the strength of the coats, the pressure in the vessel, and other causes.