1. Andrews, K. R., and Meuther, R. 0. (1941). J. Lab. clin. Med., 26, 675.
2. Carter, A. B., and Maclagan, N. F. (1946). Brit. med. J., 2, 80.
3. Cooper, I. S., Rynearson, E. H., and MacCarty, C. S. (1951). J. Lab.
4. clin. Med., 38, 689. de la Huerga, J., and Popper, H. (1950). Ibid., 35, 459.
5. Flynn, J. E., and Irish, 0. J. (1946). Science, 104, 344.