Viscosity and Clotting of Blood in Venous Thrombosis and Coronary Occlusions.

• In a recent paper on thixotropy of blood and proneness to thrombus formation, Dintenfass stressed four important points. (1) Human blood, normal as well as abnormal, exhibits thixotropy and consequently red cells are aggregated in a reversible manner both in normal and abnormal blood. (2) Viscosity of blood in a few cases of thrombosis and coronary occlusion was found to be up to tenfold greater than that of normal blood. (3) The initial stages of clotting appeared to proceed along different rheological pathways if studied under different rates of shear. (4) It was suggested that excessive thixotropy of blood was an indicator of proneness to thrombus formation. Some of these concepts are not actually new. Fahraeus envisaged as early as 1921 a possible relationship between aggregation of red cells and thrombus formation. Wasilewski observed that blood was more viscous in cases of cardiac decompensation. Aksyantsev found an increase of blood viscosity in 33$ of cases exhibiting transient interruptions of cerebral blood circulation. Marin and Stefanini postulated that a sudden coagulation of the blood within an apparently intact vascular channel might result from the combined