Electron microscopic study of macrophages appearing in a stab wound of the brain of rats following intravenous injection of carbon particles.

Colloidal carbon was introduced intravenously into young rats to label circulating monocytes before the stabbing of the brain. The rats were sacrificed 1 to 14 days after the stab wound. In the rats sacrificed between 3 to 7 days after the stabbing, numerous phagocytic cells were present in the needle wound. Electron microscope study showed that some of these phagocytic cells carried intracytoplasmic carbon particles. These carbon-labelled cells showed features either of a monocyte, full-blown macrophages, or typical microglia. It is believed that they are all derived from circulating monocytes which have ingested carbon particles in circulation and thereafter invaded the stab wound.