Scanning electron microscopic studies on the red pulp of the mink spleen

In order to obtain three-dimensional information on the fine architecture of the red pulp of the mink spleen, especially the circulation pattern in the red pulp, perfusion-fixed and freeze-cracked specimens were examined with a scanning electron microscope. A latticework was formed by elongated endothelial cells (rod cells) with side processes and the spongy reticular tissue. The outer surface of the sinus was covered with fine processes of reticular cells. Numerous sheathed arteries were found in the splenic cord. The sheath was composed of a few layers of flat reticular cells. The arterial capillaries of the red pulp opened directly into the cordal space. No evidence could be detected to prove or suggest any direct continuity between arterial capillaries and splenic sinuses. These results strongly support the concept of "open circulation", at least in the red pulp of the mink spleen, with the possibility of a "functionally closed circulation" under some physiological conditions.