抄録
Recent immunobiological studies have well established that the lymphoid tissue plays a basic role in specific defense mechanism. Although the ontogenic studies were completely done by several prominent investigators, such as Maximow, Hammar and Norris etc, it seems worthwhile to re-examine the development of human lymphoid tissue from newly arized viewpoints.
In this paper chronological relation of lymphocytic maturation among thymus, tonsils, mesenteric lymph nodes, appendix and spleen were discussed from the histological studies on the lymphoid organs taken from twenty eight fetuses ranging from four weeks to twenty four weeks of gestational age.
This study emphasizes the follo wing results.
1) Thymic lympho-epithelial tissue originates only from entodermal epithelia and has no relation with ectodermal epithelium of sinus cervicalis.
2) Lymphocytes appear first in the thymus and mesenteric lymph nodes almostly at the same time before the ninth gestational week, more numerous lymphocytes come o ut in the mesenteric lymph nodes than in the thymus.
3) Tonsils which originate at an ectodermal-entodermal junction of the second pharyngeal pouch in the eleventh gestational week become to have lymphocytes arised b y seeding after fifteenth week. The epithelial layer o f the tonsils has the ectodermal characteristics. This developing mode may be the case of the bursa of Fabricius.
4) Lymphocytes appear further later in the appendix and in the spleen by migration.
It is tempting to assume from this observations that two populations of the l ymphocyte can be exist from the beginning of development of the lymphatic tissue, and that the lymphocytes seeded into various lymphatic apparatus may differentiate into imm unologically active phases under the controls of different inductive abilities of either ectodermal or entodermal elements.
