68 The Lymphocyte and Lymphocytic Tissue 



lymphocytes injected into the blood find their way into the bone marrow, 

 and it is believed that some of these divide to form new cells in the bone 

 marrow. 



The lymphoid tissue of the mucosa of the gastrointestinal tract contains 

 about three times as many lymphocytes as are present in the blood. Lymph 

 from nonlymphoid tissue contains 200-800 lymphocytes as compared with 

 40.000-50,000 in intestinal lymph. Since the volume of intestinal lymph 

 that enters the thoracic duct in 24 hours is about twice that of the circulating 

 blood volume, about 20 times as many lymphocytes enter the blood from 

 the intestinal lymphatics as are present in the blood at any one time. These 

 lymphocytes, with those from the bone marrow, indicate a replacement of 

 blood lymphocytes in less than one hour. 



External drainage of the thoracic duct or intestinal lymphatics of rats 

 produces a loss of 30-50 million lymphocytes in one hour. After one day's 

 drainage the lymphocyte count of the lymph has fallen to about half of the 

 original figure, and by the end of four days only 8-10 million lymphocytes 

 appear in the lymph, although the volume is well maintained. At the same 

 time the lymphocytes of the blood are markedly decreased. This observa- 

 tion alone indicates that there must be a large recirculation of lympho- 

 cytes and at the same time a rapid formation of new lymphocytes. Reinfusion 

 of the lymph or the lymphocytes has until recently failed to replace the 

 decrease observed. By meticulous care in the preservation of the lympho- 

 cytes to be injected, Gowans 5 and I 4;l have been able to maintain a steady 

 flow of lymphocytes in lymph by reinfusion of the withdrawn lymphocytes 

 and even further to increase the number of lymphocytes in the lymph by 

 the infusion of additional lymphocytes obtained from lymph of other rats. 

 If lymphocytes labeled with P 32 or with Cr 59 were infused into the blood, 

 these began to appear in the intestinal lymph within two hours. Killed 

 lymphocytes did not appear in the lymph in appreciable numbers but 

 accumulated largely in the spleen and liver with only traces appearing 

 in other tissues. Following the injection of carefully prepared lymphocytes 

 which are still motile, the number taken up by the spleen and liver is much 

 less than with killed lymphocytes but is still sufficiently large to indicate that 

 circulating lymphocytes also reenter these tissues. The lung also accumulates 

 killed lymphocytes, but only a relatively few of the live lymphocytes are 

 removed by the lung. Mitotic counts of the lymphoid follicles of the spleen 

 indicate that these replace themselves once in from 6 to 12 days, but no 

 account has been taken of the lymphocytes which reenter this organ. 



The thymus supplies considerable numbers of lymphocytes to the blood. 

 By studying mitotic figures in the thymus. Kindred 4 has calculated that 

 most of the blood lymphocytes in young rats are supplied by the thymus. 



