1. Barker, D E. 1947. Arch Path. 44, 163.
2. Baumberger, J P, Suntzeff, V, and Cowdry, E V. 1942. J Nat Can Inst 2, 413.
3. Billingham, R E. 1948. J Anat Lond. In the press.
4. Billingham, R E, and Medawar, P B. 1947a. Nature 159, 115.
5. Billingham, R E, and Medawar, P B. 1947b. Ibid 160, 61.