In vivo microscopy of the spleen.

The use of improved in vivo microscopic methods has permitted a reevaluation of the "open" vs. "closed" theory of blood flow through the splenic red pulp. The microscopic methods used for studying the spleen in vivo are described as are the results, both of which were presented in motion picture form at this symposium. The results strongly suggest that, in general, there is little or no continuity of endothelium through the splenic red pulp. Instead, blood flows from "arterial" capillaries lined with endothelium into channels within the red pulp formed by the cytoplasmic processes of reticular cells. In vivo these processes appear similar to endothelium. Blood leaves the red pulp by passing through apertures in the endothelium of sinuses and venules.