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The classification of a gram-negative rod as a haemophilus rests on the demonstration of certain growth factor requirements. Classically, these have been codehydrogenases (V-factor) or iron porphyrins (X-factor), or both. Lwoff (1938) and Lwoff and Lwoff (1937) established the nature of these growth factors and inferred their functions in Haemophilus species from their known roles in other microbial systems and animal tissues, but direct studies of the function of either metabolite in Haemophilus species are rare. Smith, Hale, and O'Callahan (1953) demonstrated a direct relation between the nitratereducing activity of Haemophilus inftuenzae and the abundance of porphyrin in the growth medium. They also showed that nitrate reduction as well as catalase activity varied with the kind of porphyrin provided in the medium. We found no other reports on the utilization of the accessory factors required by the genus Haemophilus. The present work grew out of efforts to identify the growth factor requirements of a number of haemophilus-like organisms recovered from animals. It was established that all the isolates grew only when furnished a codehydrogenase or its mononucleoside derivative. No requirement for iron porphyrins could be demonstrated by conventional methods. As reference standards, a number of strains of H. influenzae, which are looked upon to require iron porphyrins as well as codehydrogenase, were also cultured on the same test media. These grew more luxuriantly on the porphyrin-containing cultures, but moderate growth was obtained consistently in six of seven cases on media lacking such enrichment. The one clear-cut difference between cells grown on heminsupplemented and unsupplemented infusion agar was that the former showed vigorous frothing on addition of hydrogen peroxide but the latter showed none. We therefore decided to measure the catalase activity of cells grown with graded amounts of hemin. MATERIALS AND METHODS

CATALASE ACTIVITY OF HAEMOPHILUS SPECIES GROWN WITH GRADED AMOUNTS OF HEMIN