The Ultrastructure of Haemostatic Blood Platelet Plugs in Rabbit Mesenterium

Abstract

SummaryHaemostatic blood platelet plugs were provoked by transection of arterioles and venules in the exposed rabbit mesentery, immersed in Zweifach’s solution at 38° C.1. Platelets from the blood stream adhered to the perivascular connective tissue as a capsule.2. The plugs consisted almost entirely of platelets, with sparse admixture of erythrocytes.3. The majority of the platelets were more or less homogeneous already after 45 seconds, but even platelets with fairly good preservation of inner structure were present. In most instances platelet membranes were intact.4. The platelets were in close contact with each other, both before haemostasis and after, the distance between the platelet membranes being 200—400 Å. Numerous pseudopods filled in the gaps between neighbouring platelets. The term “viscous metamorphosis” is discussed and criticised from an ultrastructural point of view.5. Fibrin was found at the surface of the plugs and occasionally close to the surface, but never in the interior. This lends no support to the belief that fibrin plays a mechanical role as a framework within the plug.