Abstract
Summary
The effect of penicillin in vitro varies with the concentration of penicillin, the number of organisms present, and the rate of growth of the organisms. It is most effective when rapid multiplication takes place.
Penicillin is inhibited by a substance round in resistant strains of bacteria and not in the sensitive strains tested. The presence of this inhibiting substance in resistant strains and its absence in sensitive strains suggests that resistance to penicillin may depend upon the capacity of an organism to elaborate this substance. The degree of sensitivity of any strain not producing the inhibiting substance appears to be correlated with the rate of growth exhibited by that strain.
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