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Between August and September of 1938, 12 smooth strains of Haemophilus pertussis which had grown continuously on a human blood agar medium (20 per cent blood content at pH 6) for approximately thirty to four hundred and fifty generations and 5 rough strains which had been acclimated to and had grown continuously on a veal brain agar medium for approximately four hundred to six hundred generations were each retested, and the minimum lethal doses for both smooth and rough strains were determined. The organisms grown on blood agar responded to all the tests for a smooth, phase 1 organism despite the fact that they had been grown for from six months to five years on this medium. The rough strains had been grown from five to seven years on veal brain agar without any change in characteristics. The minimum lethal dose was the lowest number of milligrams of wet
TOOMEY JA, TAKACS WS. ATTEMPTS TO ENHANCE VIRULENCE OF HAEMOPHILUS PERTUSSIS BY SERIAL PASSAGE IN GUINEA PIGS. Am J Dis Child. 1940;59(1):94-96. doi:10.1001/archpedi.1940.01990120096009