Thayer and Fabyan, in an examination of the radial artery from birth to old age, found that, in general, the artery strengthens itself, as more strain is thrown upon it, by new elastica in the intima and connective tissue in the media and adventitia. Up to the third decade there is only a strengthening of the media and adventitia. During the third and fourth decades there is also distinct connective tissue thickening in the intima. "In other words, the strain has begun to tell upon the vessel wall, and the yielding tube fortifies itself by the connective tissue thickening of the intima and to a lesser extent of the media." By the fifth decade the connective tissue deposits in the intima are marked, there is an increase of fibrous tissue upon the medial side of the intima and, in lesser degree, throughout the media. "Finally, in these sclerotic vessels degenerative changes set in, which are somewhat different from those seen in the larger arteries, consisting, as they do, of local areas of coagulation necrosis with calcification, especially marked in the deep layers of the connective tissue thickenings of the intima, and in the muscle fibers of the media, particularly opposite these points. These changes may ... go on to actual bone formation." The mesenteric artery differs in some respects from the radial, but in the main, the changes brought about by age are the same. Thayer and Fabyan note two striking points of difference: "(1) calcification is apparently much less frequent than in the radials; (2) in several cases plaques were seen with fatty softening of the deeper layers of the intima and superficial proliferation--a picture which we have never seen in the radial." (See Fig. 2.) [Illustration: Fig. 2.--Cross-section of a coronary artery, x50, showing nodular sclerosis. Note the heaping up of cells in the intima, the fracture of the elastica, and the destruction of the media beneath the nodule. The primary lesion evidently was in the media. The thickened intima is the effort on the part of nature to heal the breach. At such places as shown here aneurysms may form. (Microphotograph.)]