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The effect of subcellular fractions of the endothelia kupffer cells on blood clotting was studied. Cells were obtained from the rabbit liver by magnetic fractionation and the subcellular structures were than isolated from them by differential centrifugation. The inner membranous structures were found to carry thromboplastic activity. No correlation was found between the blood-clotting potential of the intracellular structures of the endothelial cells and the level of their cathepsin C activity.

The article deals with histological properties of the endothelium of the major vessels in mammals and in man. Biological features of this tissue and analysis of its organization are discussed. The material presented justifies consideration of the endothelial lining of the major vessels and veins as a specialized tissue of the vascular system which retains its capacity of capillaroformation. Its epitheliomorphic character and belonging to the angiodermal type of tissues are beyond doubt.

The present studies show the presence of a singular structure: a myoepithelial syncytium with the bases of the cells being embedded in a hypertrophied basal lamina containing collagen, in which bundles of muscular fibers also penetrate. The cells forming a vascular pseudo-endothelium are probably immobilised haemocytes.

A simple technique is described for maintaining in organ culture segments of blood vessel in such a way that the endothelium can be studied en face. The behaviour of such cultures throws further light on the interaction between endothelium and intravascular clotting.

The article presents a review of present day literature data on the structure of the smooth-muscle cells of vertebrates in the norm and pathology. The smooth-muscle cells of blood vessels and internal organs of vertebrates possess a contractile apparatus the same as in striated muscle and are characterized by two main functions: contractile and synthetical. The latter manifests itself in the capability of the muscle cells to synthesize all the components of the interstitial matter. General pathology of the smooth muscle includes disorders of ultracirculation, metabolic disturbances, necrobiotic changes and necrosis of the muscle cells, compensatory-adaptive processes predominantly of the type of hyperplastic-hypertrophic reaction and regeneration.