Open circulation in the human spleen, Dissection scanning electron microscopy of conductive-stained tissue and observation of resin vascular casts.

Human spleen specimens conductive-stained by the tannin-osmium method were microdissected under the scanning electron microscope and it was revealed that arteries open through one or two end-pores (3-4 mu in diameter) into the reticular cell meshes in the Billroth cord and in the perifollicular area. The endothelial cells lining the arterial terminal portion, which may be swollen into a saccular space, are perforated intracellularly. Dumb-bell shaped erythrocytes are seen passing through these side-pores (1-2 mu in diameter). The termination of arteries not in sinuses but in the cordal reticulum was also confirmed by scanning electron microscopy of blood vascular casts of methacrylate resin. These findings evidence that the "open" theory is valid in the human spleen.