A surgically obtained spleen was perfused with saline and with a glutaraldehyde solution. After fixation the tissue blocks were treated with tannin-osmium impregnation technique and dehydrated. The blocks immersed in ethanol or isoamyl acetate were quench-frozen in liquid nitrogen and cracked to be observed in a field emission scanning electron microscope.
1. The sinus is lined by rod cells connected by their transverse processes which have long been believed lacking in primates. Oval perforations persistently communicate the sinus lumen and the spaces in the Billroth cord.
2. Cell junctions are demonstrated between the lateral processes of rod cells. Vesicular, villous and thread-like microprojections are on the rod cells.
3. The Billroth cords are formed by reticulum cells of stellate form and smooth surface. In their meshes are caught round cells of various types, the predominant being neutrophils. Blood platelets are numerous and some form a rosette on macrophages.
4. Macrophages occur numerously in the cordal meshes, some of them projecting into the sinus lumen. Covered densely by cytoplasmic microprojections, they are believed to be independent cells; no gradations between them and the cordal reticulum cells are recognized.
5. Structures are found suggesting the ends of the penicilli open into the cordal spaces. The mode of hanging of erythrocytes on the sinus wall indicates a blood flow from the cord to the sinus, favoring the “open theory” in the human spleen.
6. The structure of the sheathed artery and other blood vessels in the spleen are depicted.