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