There may be produced in rabbits by the intravenous injection of large doses of diphtheria toxin a vascular degeneration involving the entire aorta, the carotids to the base of the skull, the subclavians, and iliacs, and, for a varying distance distally, the brachials, femorals, and large abdominal vessels. The first part of the pulmonary artery is sometimes affected. The lesion is practically diffuse throughout the aorta and vessels mentioned, consisting of a fatty degeneration and necrosis of the smooth muscle in a wide zone of the media and a crowding together of the elastic fibers in the region affected, resulting in an irregular thinning of the vessel walls and many small aneurysmal pouchings. In rabbits which received pituitrin with the diphtheria toxin extensive calcification occurred throughout this degenerated zone, both in the aorta and other large vessels. It is believed, however, that pituitrin is not essential to the calcification and that if it is of any importance it is because an extreme fatty degeneration is produced more quickly in the media of the vessels when it is administered simultaneously with the toxin.

Diphtheria toxin, given in large doses intravenously, produces in the kidneys of the rabbit a pronounced vascular and parenchymatous degeneration. The former consists of a swelling and desquamation of the endothelial cells of the arterioles and small veins with the formation of fibrinous thrombi, a necrosis and thrombosis of the capillaries of the tufts with hemorrhage and the formation of fibrinous and hyaline masses, and in some of the affected glomeruli considerable collections of polymorphonuclear leukocytes.

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