During the past two school years, prophylactic injections of whooping cough vaccine have been given to large groups of primary grade and preschool children in the Fresno public schools.
The vaccine used was the undenatured antigen of Haemophilus pertussis described by Krueger, Nichols and Frawley.1 The method consists essentially of disrupting living bacterial cells by mechanical means and obtaining the endocellular elements by ultrafiltration. Recently isolated smooth strains of Haemophilus pertussis are grown on Bordet's medium enriched with human blood. The cells are harvested in buffered isotonic solution, thoroughly washed to remove metabolites, and mechanically disrupted in a ball mill. The resultant suspension is subjected to ultrafiltration through acetic collodion membranes whereby all intact cells and large particles are retained, while material in molecular or colloidal solution passes through. The water-clear filtrate contains the antigen. Micro-Kjehdahl determinations are made to determine the nitrogen content of this antigen solution.