- 17 - media after 20 years of age, and emphasized that such deposits increase with age and precede the formation of intimal plaques. Blumenthal et 1. also observed that the ratio of calcium phosphate to calcium carbonate in the aortas is similar to that in bone. It should be pointed out here that whether or not the calcium deposits in blood vessels may be regarded as an irritant leading to damage and repair in the formation of, plaques, there are subtle to obvious changes in parts of some blood vessels (e.g., aorta, coronary arteries, renal arterioles) that somehow provide a receptive environment for deposition of calcium (dystrophic calcification), Calcium deposition may be especially marked in conditions involving excessive demineralization of bone, as in advanced osteoporosis of aging, osteitis fibrosa, and parathyroid disorders, from whatever cause. and with elevation of blood levels of calciun, The deposition of calcium in blood vessels as a consequence of damage of bone of experimental animals after internal administration of substantial doses of bone-seeking alpha emitters has been observed, ¢} Elkeles (to whom the author referred) pointed out that certain radioactive substances are deposited with the calcium in the skeletal system. He reported that in elderly patients, the alpha particle activity per unit net weight of aorta, although variable, tended to follow the degree of calcification. He studied the abdominal aorta, coronary arteries, pulmonary artery, and ribs and costal cartilage. Ash % and alpha activity rose with age only in the aorta and coronary arteries. In pulmonary arteries, ash % did not rise and alpha activity declined with age. Pulmonary arteries were chosen as the control arteries because they are histologically similar to aorta but not subject to atherosclerosis except