EFFECT OF THYMECTOMY ON HEMATOPOIETIC ORGANS OF THE OPOSSUM "EMBRYO".

Summary Opossums were thymectomized when lymphatic tissue had developed in some lymph nodes but not in the spleen. They were sacrificed 2 weeks later. Lymph nodes were grossly deficient in small and medium lymphocytes and lymphatic tissue did not appear in the spleen. Myeloid tissue not only persisted but was found greatly increased in amount at a time when it would have normally decreased. Maturation and proliferation of this tissue was abnormal, being characterized by maturation arrest and ineffective erythropoiesis. These findings indicate that the thymus influences the origin of lymphatic tissue, at least in the spleen, maintenance of lymphatic tissue in lymph nodes, and suppression of myeloid tissue in lymph nodes and spleen.