Evidence for a humoral thymic factor in rabbits.

Rabbits thymectomized between 12 and 36 hours after birth subsequently show reduced levels of circulating lymphocytes together with a lowered immunological response to human γ-globulin. These effects of thymectomy can, to a large extent, be prevented by means of intraperitoneal auto-transplants of thymus in a Millipore diffusion chamber. It appears possible that the epithelial-reticular cells of the transplant persist in the diffusion chamber and elaborate a humoral factor, or factors, which take part in the maturation of antibody-producing cells.