The synovium from six patients with hemarthrosis was studied, and the results were compared with those previously obtained from a study of experimental hemarthrosis in the rabbit. It was concluded that in both instances many shed erythrocytes escape from the joint by passing between synovial cells. Some erythrocytes,
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however, are phagocytosed by these cells. Next fragmentation of the erythrocyte occurs. This is followed by the formation of unicentric or multicentric whorled bodies and siderosomes.