15. =Pulmonary Vessels.= Character of walls and contents. Normally the intima is smooth, grayish-white and translucent. Fatty degeneration of the intima is not rare (acute infections and intoxications); atheroma and aneurismal dilatation are infrequent. Occasionally parietal thrombi and thickening of the wall due to organization of a thrombus are seen. The pulmonary arteries are normally empty or contain soft cruor or agonal white clots. These are not adherent to the wall, do not fill the lumen and are soft and moist. Emboli fill the lumen as if forced into it (at the branchings of the artery they form “rider’s” emboli); they are more dry and brick-red, brownish or grayish in color. Occasionally they may be unrolled into long fibrinous strands. Older emboli may show more or less organization and adherence to the vessel-wall. In air-embolism the pulmonary arteries contain a mixture of blood and air looking like a stiff-beaten white of egg of red color. Large emboli of liver-tissue or liver-cells may be found in the pulmonary arteries after traumatic rupture of the liver. Fat-emboli of the smaller arteries can be recognized by the naked-eye. Thrombosis of both pulmonary arteries and veins is very common in chronic valvular lesions, pneumonia, terminal infections, burns of the skin, poisoning with hemolytic agents, etc. 16. =Great Vessels of Thorax.= Note size of lumen, condition of walls, particularly of intima, and the contents. Circumference of thoracic aorta 4.5-6.0 cm., thickness of wall 1.5-2 mm. Test elasticity of wall by stretching; note if it retracts and becomes shorter than the œsophagus, which was cut at the same level. Note consistence of wall (stiff and hard in sclerosis and calcification). Normally the intima of the aorta is smooth, grayish-white and semitranslucent; the wall is elastic. Fatty degeneration, sclerosis, atheroma and aneurismal dilatations are the most common pathologic findings. Fatty degeneration shows itself in yellowish spots or streaks, more opaque and slightly elevated. Sclerotic areas are hard, white and tendon-like. Atheromatous “plaques” and “ulcers” are white or yellowish, elevated, rough, scaly, with loss of substance, often more or less calcified. Thrombi are frequently formed upon such atheromatous patches. Hemorrhage into the intima may occur (aneurysma dissecans). Radiating or linear sclerotic folds and depressions in the intima, with or without dilatation of the lumen, usually result from syphilis (mesaortitis). A dirty brownish discoloration of the intima is due to an imbibition of diffuse hæmoglobin, usually postmortem. In chronic icterus the intima may be bile-stained. Thrombosis of the aorta is not common. Congenital or acquired stenosis at the isthmus is rare. Tuberculosis of the aorta-wall is also very rare.