Hornibrook (1939) described a liquid medium for the propagation of Hemophilus pertussis having a casein hydrolyzate base to which were added various salts, starch, cysteine, and nicotinic acid and which was capable of growing recently isolated strains. Because of the potential advantages of such a medium, it has been studied by many investigators. Their work has confirmed Hornibrook's original observations but it has also revealed several disadvantages in the medium. Modifications of the original formula stated to prevent precipitation, simplify preparation, decrease the granularity of growth, and increase the final bacterial count have been suggested by Verwey and Sage (1945), Wilson (1945), Farrell and Taylor (1945), and Cohen and Wheeler (1946). It is the purpose of this report to describe further the medium that has been developed in our laboratory and to define the cultural conditions that seem optimal for the growth of H. pertussis in this medium. Some observations concerning the antigenic properties of the liquid medium cultures are included. EXPERIMENTAL METHODS AND RESULTS

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