The bursa of Fabricius is a structure peculiar to Aves. It is a blind sac connected by a small duct to the dorsal part of the cloaca. Often nicknamed “the cloacal thymus,” the function of the bursa is believed to be similar to that of the thymus (Riddle, 1928; Taibel, 1938). There is no question that the bursa of Fabricius functions as a lymph gland during the first two to three months after the chicken hatches (Jolly, 1914; Calhoun, 1933; Glick, 1955). Like the thymus, the bursa in birds is believed to have some endocrine function in relation to growth and sexual development. (Riddle, 1928; Woodward, 1931; and others.)

Although reticular cells of lymph glands and lymphocytes may participate in globulin and antibody synthesis (Raffel, 1953), suspicion regarding the importance of the bursa in antibody production arose in the following accidental manner. A source of chicken blood possessing a high …