[Ultrastructure of unstabilized fibrin].

The structure of non-stabilized fibrin was studied by electron microscopy. Non-stabilized fibrin was shown to consist of a network of fibers (fibrils, from 2 to 10 mu in length, and up to 200 A in width). Negative contrasting with uranyl-acetate demonstrated non-stabilized fibrils to be made up of 5 to 10 longitudinally striated protofibrils and to be characterized by transverse striations with the main period of about 200 A. Comparison of the ultrastructure of stabilized and non-stabilized with factor XIIIa fibrin fibers demonstrated their morphological affinity.