Abstract
SUMMARY: Fifteen strains of Haemophilus influenzae were found to require for growth, in addition to coenzyme 1 (diphosphopyridine nucleotide; DPN) and haematin, the following substances: pantothenic acid, thiamine, uracil. Some of the strains also required a purine, accepting xanthine, hypoxanthine or guanine, but not adenine. Cysteine (or glutathione) was also needed for luxuriant growth. A medium is described which yields crops of about 1010 organisms/ml. after incubation for 18 hr. at 34°. Sheep red cells, but not horse red cells, contain a DPN-ase, located in the stroma, which rapidly destroys any DPN added to them and also destroys the contained DPN when the cells are lysed.