a1 Glaxo Laboratories Ltd., Greenford, Middlesex
1. One hundred and eighty-seven freshly isolated strains of Haemophilus pertussis, together with ten laboratory strains and eleven strains of H. parapertussis were submitted to tests of their morphological, biochemical and antigenic properties in relation to their virulence to mice.
2. The naturally occurring H. pertussis strains form a single antigenic type differing from that of the attenuated laboratory strains.
3. H. parapertussis forms, as previously claimed, a distinctive type with characteristic properties closely related to H. pertussis.
Our thanks are due to Col. H. J. Bensted, Prof. J. W. McLeod and Drs A. Beck, D. G. Evans, G. Eldering, J. Marks, M. T. Parker, M. Pittman and H. Proom for supplying strains used in this investigation.
(Received April 27 1954)