Abstract
The spleen of the rabbit was thoroughly washed with physiological saline via the lienal artery and then perfused with 2.5% glutaraldehyde. After ligation of the lienal vessels the excised spleen was further fixed for several days. Observation under the scanning electron microscope of small cubes cut from the spleen gave the following results on the fine structure of the red pulp:
1. The wall of the splenic sinus revealed the structure of a perforated lattice formed by longitudinally extended rod cells and by their transverse cytoplasmic processes.
2. The nuclei of the rod cells were conspicuously projected into the sinus lumen and tended to be grouped in certain areas of the endothelium.
3. The transverse processes of neighboring rod cells were connected into intercellular bridges; the possible cell boundary was suggested only occasionally by an inconspicuous crest on the surface.
4. A characteristically twisted course of the rod cells was found at the corner of sinus ramifications and was thought to be related to the sphincter mechanism of the splenic sinus.
5. The luminal surface of the rod cells was provided with irregular microprojections, some of which were drumstick-shaped microvilli while others were cytoplasmic threads of conspicuous length.
6. The perforations in the lattice of the sinus represented direct continuations of the sinus lumen to the spaces in the cord of Billroth which contained a few blood cells.
7. The reticulum cells of the cord sent their foot-like processes from outside to line the sinus lattice. No naked reticulum fibers could be recognized in the red pulp.
