Lymphocytic Life Span and Turnover 69 



This and labeling techniques indicate a replacement of thymic lympho- 

 cytes in rats once every two and one-halt days. Labeled circulating lympho- 

 cytes also reenter the thymus in considerable numbers. Similar studies 

 of lymphocytes in lymph nodes indicate a rapid mitotic replacement of 

 lymphocytes. Circulating labeled lymphocytes also reenter the lymph nodes 

 in common with all lymphoid tissue. 



Transfused lymphocytes do not remain in the blood but are there for a 

 short time and disappear in from one to three hours. The disintegration 

 of lymphocytes in the blood is not great, as lymphocytes added to blood 

 in vitro remain motile for much longer times. 



Only a few lymphocytes are excreted into the lumen of the intestine, as 

 very few are found in the surface layers of the intestinal mucosa as compared 

 to the larger numbers found in the deeper layers. Transfused P 32 -labeled 

 lymphocytes from the thoracic duct leave the blood rapidly, and most are 

 found in the lymphoid tissue, depending on the viability of the lymphocytes 

 transfused. Van Dyke and Huff" radiated one member of parabiotic rats 

 to destroy his circulating white cells and calculated the white cells transfused 

 to this rat from his otherwise normal parabiotic partner. The average sur- 

 vival time of the granulocytes in the blood of the recipient rat was 23 minutes 

 and that of the lymphocytes was 170 minutes. Farr 7 found that labeled auto- 

 genesis lymphocytes from lymph nodes of the rabbit disappeared from the 

 blood within 90 minutes. Transfused lymphatic leukemia cells leave the blood 

 in about one hour. White 8 transfused blood from men who had received 

 Atabrine (which labeled the leucocytes) into recipients and found that the 

 leucocytes had disappeared from the arterial blood in from 30 to 90 minutes. 

 Gowans 5 recovered 80 per cent of the lymphocytes transfused into the 

 blood from the lymph of the thoracic duct. Certainly there is a large and 

 rapid migration of lymphocytes from the blood to the lymphoid tissues and 

 to the lymph. The number of circulations seem adequate for the individual 

 lymphocyte to visit most of the lymphatic tissue of the body. The daily 

 output of lymphocytes in the thoracic duct of a dog weighing 10 kg. was 

 found to be 5.078 million daily and that of man was estimated to be 35,550 

 million each day. 



From the data available Osgood 9 has calculated that the life span of the 

 lymphocyte in the human is 100 days. Less definite information is available 

 for the large and medium lymphocytes. The many factors involved in cal- 

 culating the life span of lymphocytes and the lack of precision in the calcula- 

 tion of each of these would make this estimate an approximation. 



