Abstract
Summary
1. The maximal dosage of p-aminobenzoic acid for the chick embryo (2 mg) is effective in inhibiting the growth of rickettsiæ of the spotted fever group in the following order of magnitude: Rocky Mountain s. f. > Brazilian s. f. > Colombian s. f. > South African tick f. > fièvre bouton-neuse. There was much more inhibition of the American group than of the African spotted fevers.
2. p-Aminobenzoic acid was about twice as effective on Rocky Mountain spotted fever infection (46% survivors) as on either epidemic or murine typhus (20% and 26% survivors, respectively).
3. p-Aminobenzoic acid did not appreciably inhibit the growth of the agents of “Q” fever, tsutsugamushi, lymphogranuloma venereum, or psittacosis.
4. Studies on the mode of action of p-aminobenzoic acid indicate that not only must the amino and carboxyl groups remain intact and in the para position with respect to one another, but the total size of the molecule must not be altered, if the inhibitory properties are to be retained. Such a high degree of specificity suggests that paba may be acting on an enzyme system.
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