Abstract
Method: The lungs of a pithed cat are aerated by Meltzer's method of intra-tracheal insufflation, temporarily interrupted once per minute. A constantly inflated lobe is carefully elevated from the open thorax and its margin fixed by two serrated clips. If an area near the margin is transilluminated by a suitable optical system the alveoli with their related blood vessels can be directly observed and studied by means of a horizontally arranged microscope magnifying 50 to 100 diameters.
Owing to the wall-thickness of the intra-lobular arteries and veins and their immediate branches, the circulating blood is only visible in the smaller vessels, i. e., (a) in the pre-arterioles and arterioles passing between the alveoli, (b) in the capillary network formed on the surface of the alveoli and embracing the air cells and (c) in the smaller venules before they merge into the efferent intra-lobular veins.
Circulation in Vessels of Different Size: In the pre-arterioles the blood stream is often clearly visible. The cellular elements are in densely packed mass formation, the flow is pulsating with a rapid systolic forward movement and a diastolic decrease in velocity, amounting occasionally to a total stoppage of the flow in diastole. Expansion and relaxation of the walls is not observed. In the arterioles the stream is no longer pulsating, the individual blood cells are distinguishable and travel in ranks of two to six. In the capillaries, the blood corpuscles travel in single file, and in a continuous stream, but the rate of flow varies in different capillaries even in the network surrounding the same alveolus. In the smaller venules the stream is constant and a little more rapid than in the capillaries. Individual cells are distinguishable and eddies often occur at the junctions. In still larger venules and the smallest veins the stream is no longer constant, but a definite pulsation occurs, the onward flow tending to be reduced during systole and increased during diastole.
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