Thymic and Thoracic Duct Contributions to Blood Lymphocytes in Normal and Thyroxin‐Treated Guinea‐Pigs

The percentage and number of lymphocytes were compared in thymic‐vein, carotid‐artery and femoral‐vein blood of guinea‐pigs. The lymphocyte populations of thymic‐vein blood and thoracic‐duct lymph were subdivided into groups of lymphocytes classified by their mitochondrial content (MC). Normal animals and thyroxin‐treated animals were investigated. The following results were obtained: The percentage and number of lymphocytes were greater in thymic‐vein blood than in both carotid‐artery and femoral‐vein blood, indicating an emigration of lymphocytes from the thymus. The thoracic‐duct lymph contained a much greater proportion of“larger” lymphocytes, characterized by higher mitochondrial content, than the blood. After an initial decrease (6 hrs after injection), thyroxin caused a pronounced increase in the incidence of lymphocytes with medium and high mitochondrial content in the blood. This increase was preceded by a similarly increased incidence of lymphocytes with medium and high mitochondrial content in the thorac: c‐duct lymph.