In 1956, Bruce Glick showed that removal of the bursa in newly hatched chicks severely impaired the ability of the adult birds to produce antibodies. In contrast, removal of the bursa in adult chickens has little effect on the immune system. This was a serendipitous discovery that came about when a fellow graduate, Timothy S. Chang, who was teaching a course on antibody production obtained chickens from Glick that had been bursectomised (removal of the bursa). When these chickens failed to produce antibody in response to an immunization with
Staphylococcus bacteria, the two students realized that the bursa is necessary for antibody production. Their initial attempts to publish their findings were thwarted by an editor who commented that "further elucidation of the mechanism ... should be attempted before publication.” The role of the
thymus in the immune response was also identified shortly after the discovery of bursa's role in antibody responses. In thymectomized animals, the ability to reject
allografts, and to mount delayed
hypersensitivity responses, was drastically reduced. By the mid-1960s, immunologists were convinced that there were indeed two separate arms of the immune system: one dealing exclusively with the production of circulating antibodies (
humoral immunity), and another that is involved in the delayed hypersensitivity-type reactions and graft rejections (
cell-mediated immunity). ==Diseases==