There is even occlusion of many arterioles. Changes in other organs as the result of arteriosclerosis of their afferent vessels occur, but are not so characteristic as in the kidney. In the brain the result of gradual thickening of the arterioles is a diminished blood supply, softening of the portion supplied by the artery, and later a connective tissue deposit. The occurrence of thrombi is favored and, now and again, a thrombus plugs an artery which supplies an important and even vital part of the brain. The arteries of the brain are end arteries, hence there is no chance for collateral circulation. It is therefore evident how serious a result may follow the disturbance in or actual deprivation of blood supply to any of the brain centers or to the internal capsule. =Arteriosclerosis of the Pulmonary Arteries= There have been a number of cases of sclerosis of the pulmonary arteries, either alone, or associated with general systemic arteriosclerosis. A primary and a secondary form are recognized, the former in conjunction with congenital malformations of the heart, the latter as the result of severe infection or of mitral stenosis. These two causes seem to be the most important in the production of the arterial changes. The cases thus far described have revealed widespread thickening of the pulmonary arteries. If one may judge by the description of the pathologic changes, the condition is quite similar to that produced in a vein by transplantation along the course of an artery. The diffuse form with connective tissue thickening of all coats has been generally described. There is also obliterating endarteritis of the smaller vessels. In the etiology of the condition severe infection seems to play a prominent rôle. The constant presence of right ventricular hypertrophy is interesting, the heart dullness extends, as a rule, far to the right of the sternum. In some of the cases no demonstrable changes were observed in the bronchial arteries or in the pulmonary veins. Sanders has described a case of primary pulmonary arteriosclerosis with hypertrophy of the right ventricle. Recently Warthin[2] has reported a case of syphilitic sclerosis of the pulmonary artery which places the lesion in exactly the same category as that of syphilis in the systemic arteries. There was also aneurysm of the left upper division present and, to settle the etiologic nature of the process, Spirochete pallida were found in the wall of the aneurysm sac and in that of the pulmonary artery. The microscopic picture in the pulmonary artery could not be told from that in a syphilitic aorta. [2] Warthin, A. S.: Am. Jour. Syph., 1918, i, 693. =Sclerosis of the Veins=