“…Their work demonstrates that 19-nortestosterone and related analogs (Aspinall et al, 1959) not only inhibit the growth and development of the bursa of Fabricius, but also retards the development of other lymphoid tissues. Chang et al (1955Chang et al ( , 1957Chang et al ( , 1958 have surgically demonstrated that the bursa of Fabricius singly and in combination with the spleen is necessary during development in order that birds may subsequently be able to form antibodies. Chemical extirpation of the bursa and reduction of other lymphoid tissues using 19-nortestosterone also blocks the bird's subsequent ability to form antibodies (Mueller, Wolfe and Meyer, 1959).…”