The Sites at Which Plasma Clearing Activity Is Produced and Destroyed in the Rat

Clearing activity has been produced by perfusing blood containing heparin in concentrations of from 2·5 to 0·025 i.u. per ml. through the isolated hind limbs of rats. It is produced also by the lung, the abdominal viscera with the exception of the liver, and the skin and subcutaneous tissue. The experiments indicate that the liver does not produce clearing activity. 2. The appearance of clearing activity in blood perfused through the isolated hind limbs of rats fed olive oil 4 to 5 hours previously, indicates that clearing activity in such animals is produced in part by the hind limb circulation. 3. Both in rats which have received an injection of heparin and in fat‐fed rats, clearing activity of the blood from the hepatic vein was less than that of the aortic blood. Blood from the portal vein, the inferior vena cava, and the aorta had similar clearing activity. 4. Perfusion of heparinized blood through the isolated liver resulted in a fall in its clearing activity. This loss indicates that this organ destroys clearing activity.