1. Girard, G., Ann. Rev. Microbiol., 9, 253 (1953).
2. Meyer, K. F., J. Immunol., 64, 139 (1950).
3. Rutqvist, L., Thal, E., and Åberg, E., Acta Path. Microbiol. Scand., 39, 94 (1956).
4. Schütz, H., Brit. J. Exp. Path., 13, 284 (1932).
5. Thal, E., Ann. Inst. Pasteur, 91, 68 (1956).