Phagocytosis of colloidal carbon in a lymph node.

Colloidal carbon, injected intramuscularly, migrates rapidly and selectively to a corresponding lymph node by lymphatics, in which the carbon travels as free particles. In the lymph node, carbon particles are mainly phagocytosed and stored by macrophages, which exhibit morphologic changes in the plasma membrane and the tubules of endoplasmic reticulum. The subsequent migration of these cells results in wide distribution of carbon in the lymph node. Cytoplasmic changes also occur in sinusoidal macrophages, in which no carbon is seen. A possible relation of these macrophages to macrophage migration in lymph node is postulated. The lymphatic endothelial cells, like endothelial cells in any other organ, phagocytose only a small amount of carbon and only after functional overload of the macrophages.