Experimental Studies on the Chief Source of Blood Lymphocytes in Adult Rabbits

In adult rabbits, chief lymphoid organs such as the mesenterial lymph nodes, vermiform appendix and spleen, as well as other several small lymph nodes, were removed. The total weight of the removed lymphoid organs amounted to approximately 80 per cent of that of the entire lymphoid organs. In the rabbit the mesenterial lymph nodes unite in a large mass called pancreas Aselli, the weight of which is about one and a half of the sum of all the other lymph nodes.Simultaneous extirpation of the chief lymphoid organs mentioned above and other several small lymph nodes resulted in a marked drop of the number of the blood lymphocytes, down to 30 to 40 per cent of the pre-operative values, and such a pronounced lymphopenia persisted for several weeks. No other remarkable alterations were observed in the blood picture, except for a post-operative non-specific granulocytosis which subsided rapidly. The continuity of the lymphatic pathway interrupted by the removal of the mesenterial nodes has been rapidly re-established.Removal of the mesenterial mass of lymph nodes alone was responsible for a marked fall of the blood lymphocyte counts, so long as this mass was well developed and its weight greater than 1/2000 of the body weight. But when the relative weight of this mass was below this level, the removal of this mass was followed by little or on reduction of the blood lymphocytes.Appendectomy combined with splenectomy alone caused no significant drop-of the blood lymphocyte counts. However, when the mesenterial mass of nodes was too small in size to induce a perceptible lymphopenia after its removal, the subsequent extirpation of the vermi- form appendix and spleen on the 7th day produced a remarkable reduction of the blood lymphocytes.These findings indicate that, in the adult rabbit, the mesenterial mass of lymph nodes represents the chief source of the blood lymphocytes together with the vermiform appendix and spleen, the latter two organs being auxiliary to the former one.