The Appearance of Labeled Cells in the Thoracic Duct Lymph of the Guinea Pig after the Administration of Tritiated Thymidine

Tritium-labeled thymidine was given by either intraperitoneal or intravenous injection to 13 male guinea pigs of approximately 400 Gm. weight.

At times varying from 1 hour to 30 days after the administration of thymidine, thoracic duct lymph was obtained and examined for the presence of labeled cells.

After a single dose of thymidine, a steady stream of labeled lymphocytes, ranging from 2 to 7 per cent of the total cells, enters the blood over the period studied. The intensity of the labeling appears to diminish gradually.

Labeled large and medium lymphocytes were found in the lymph during the first hour. Labeled small lymphocytes began to appear in the fourth hour, in small numbers, and thereafter increased, whereas the proportion of labeled large and medium lymphocytes steadily diminished.

This sequential appearance of large, medium and small lymphocytes is interpreted as indicating the pattern of development of the cell series. The labeled small lymphocytes appearing in the lymph are considered to be newly formed from precursor cells located in the various lymphatic tissues.