1. Standen, O. D., Brit. Med. J., ii, 20(1955).
2. Norton, S., and deBeer, E. J., Amer. J. Trop. Med. Hyg., 6, 898 (1957).
3. DeBell, Jean T., del Castillo, J., and Sanchez, V. (in the press).
4. Goodwin, L. G., and Vaughan Williams, E. M., J. Physiol., 166, 44P (1963).