Exchanges of proteins, especially fibrinogen, between blood and lymph.

Microvessels of rat mesentery were used for the study. Proteins marked with fluorescent dyes are first visible in the vascular terminations. After 10 minutes they pass into the perivascular tissues where very fine reticular structures appear. The passage begins at the level of the venules, and continues in the interstitial tissue in the form of fibrils; the extravasation does not have a diffuse character (this has also been verified by other techniques). The ultraviolet microscope permits localization of the proteins because of their specific absorption. These experiments were conducted with labelled fibrinogen. Fibrinogen showed a high degree of selective affinity for the vessel wall, especially for that of the venules, and much less or none at all for that of the arterioles or the capillary loops. Fibrinogen is also found in the interstitial spaces and in the lymphatic vessels. The deposits in the vessel walls occur with a normal speed of blood flow. These intravenous deposit may be prevented by means of a preliminary injection of heparin. On the other hand they are very marked after inhibition of fibrinolysis by epsilon-aminocaproic acid and also by the addition of small doses of thrombin.