Further Observations on Epithelialization of Small Wounds

Linear incisions were made on the back skin of rabbits and 3H-thymidine was injected intravenously during various stages of epithelialization of the wounds. Biopsy specimens were taken 30 minutes and one to three days after injection of the tracer. In the migrating epithelium, the nuclei of basally located cells were labeled thirty minutes after the introduction of 3H-thymidine. The cells located at higher levels did not incorporate the tracer. One or two days later, labeled nuclei also appeared in the upper layers. After wound closure, nuclei were labeled in the basal layer of the epithelium 30 minutes after the introduction of 3H-thymidine. One day later, labeled nuclei appeared in both basal and suprabasal layers, and after three days the nuclei of parakeratotic surface cells were also labeled. These observations indicate that the cells which emigrate from the epidermis divide and differentiate while they move over the wound surface. Thus, mitosis and differentiation are not incompatible with migration as it has been postulated by previous workers. It is concluded that both mitotic and differentiating cells participate in formation of a protective cover over skin wounds