1. Alexander, H. E., Koch, G., Mountain, I. M., and Van Damme, O., J. Exp. Med., 108, 493 (1958).
2. Norman, A., and Veomett, R. C., Virology, 14, 497 (1961).
3. Porterfield, J. S., Bull. Wld. Hlth. Org., 22, 373 (1960).
4. Wecker, E., Virology, 7, 241 (1959).
5. Connolly, J. H., Herriott, R. M., and Gupta, S., Brit. J. Exp. Path., 43, 392 (1962).