The passage of colloidal particles across the endothelial wall of sinusoids and their accumulation in the marrow parenchyma have been studied, after an intravenous injection of a large amount of India-ink and saccharated iron oxide.
The injected colloidal particles are first deposited evenly on and in the sinusoidal endothelium within 30 minutes, and then beginn to enter into the marrow parenchyma, passing through the endothelial wall. Thereafter, the colloidal particles are rapidly taken up by the reticular cells in the parenchyma and accumulate in their cell bodies. In these processes of transportation of colloidal particles, the phagocytic activity of both the sinusoidal endothelium and the reticular cells in the marrow parenchyma seem to play a major role.
The chemically stable carbon particles are gradually brought together into large masses formed by coalescence of carbon-laden reticular cells and persist for a long time; whereas the colloidal particles of saccharated iron dioxibe phagocytized by reticular cslls disappear rather rapidly within a month or two, probably having been utilized in the iron metablism of the organism.