By making Spalteholz's preparates from the lungs of adult rabbits, mainly from the 18 experimentally induced cavities and 11 caseous foci, following the progress of these tuberculons lesions, and examining these specimens under a 3-dimentional microscope, the author has arrived at the following conclusions: 1) In the tuberculous lesions, it has been found that the blocking of the pulmonary artery occurs and subsequent blocking of pulmonary veins. 2) In the caseous foci, blood vessels are almost obliterated and occasionally newly formed blood vessels are seen around the main artery and vein as well as around their residual branches. 3) On the capsules of the caseous foci are found comparatively less vessel distribution as compared with those on the cavity walls, while stenosis and dilatation can be recognized around the branches of arterioles and venules. 4) In the periphery of caseous foci, bronchial arteries have become dilated and among the bronchial arteries and bronchial wall vessels are found newly formed arterioles and venules. 5) Around the caseous foci are found occasional anastomoses precapillary and capillary between the newly formed pulmonary and bronchial arterioles, but numbers of these anastomoses are less than the numbers of cavity-walls. 6) Blood in the bronchial artery is seen flowing even into the pulmonary artery by way of the anastomoses around the caseous foci, previously mentioned. Consequently the caseous foci are supplied with arterial blood by the bronchial arteries as well as by newly formed pulmonary arterioles. 7) In the caseous foci that have started cavitation, newly formed bronchial arterioles can be recognized on the cavity walls at the orifice of drainage bronchus. 8) Pulmonary arteries and veins distributed in the cavity are blocked before reaching the cavity; but when they remain in the cavity in the form of beam, residual vessel lumen are seen in the central part of the beam and newly formed blood vessels of networks are seen surrounding the beam. 9) When the main pulmonary artery and vein are running on the side-wall of the cavity, these vessels are compressed, narrowed, and dislocated; and aneurysm and varix-like dilatation can occasionally be recognized. 10) Capillaries distributed on the cavity wall are classified into three categories according to their origin, namely, (1) those capillary vessel-networks that are newly formed from the small branches of pulmonary artery or vein; (2) those capillary vessel networks that communicate at the main trunk of pulmonary artery or vein; (3) those capillary vessel networks that are located at the orifice of the drainage bronchus and communicate at bronchial artery. 11) Vessels on the cavity wall mentioned above make small circles immediately under the necrotic layer, and reverse to venulous vessels. All these capillaries are closely connected with each other in a network formation. 12) The bronchial arteries distributed on the cavity walls are dilated and turned and twisted. thus the bloodflow is thought to have increased; and on the side of the hilus pulmonis of the cavity, numerous precapillary or capillary anastomoses are seeu between pulmonary and bronchial artery around the drainage bronchus. 13) The degree of changes in bronchial vein is less than that observed in the brohial artery, but the vessels on the bronchial wall are proliferated. 14) New vessels are formed from pulmonary arterioles and venules in the sickened portion of caseous foci and cavities; and the intercostal, the csophageal, and the pericardiac arteries penetrate into these pleuritic regions and anastomosed with each other.