The effect of the size of the inoculum and the age of the infection on the curative dose of penicillin in experimental infections with streptococci, pneumococci, and Treponema pallidum.

The amount of penicillin which suffices to abort pneumococcal and streptococcal infections in white mice and rabbits, as well as syphilitic infection in rabbits, has been shown to increase markedly with the number of organisms inoculated. The curative dose increases also with the age of the infection, presumably owing to the interim increase in the number of organisms in the nfected host. The necessity for the larger doses of penicillin is attributed to the longer itime for which effectively bactericidal concentrations of penicillin must then be provided in order to kill the larger number of organisms.