With a note by K. E. COOPER on the theory of inhibition zones
SUMMARY: The time taken for agar plates to reach incubator temperature under different conditions was determined by thermocouple measurements. From 1 to 5 hr. was taken to reach within 1 of the incubator temperature, according to their mass, position, stacking and original temperature. Delay in heating slowed the growth of organisms and produced larger inhibition zones due to diffusing antiseptics. This leads to errors in sensitivity and thus in assay work unless technique is standardized to overcome these differences. Deviations from the calculations resulting from the formula of Cooper & Woodman (1946) can be overcome by such standardization.
CooperK.E.,
WoodmanD.1946; The diffusion of antiseptics through agar gels, with special reference to the agar cup assay method of estimating the activity of penicillin. J. Path. Bact. 58:75
MitchisonD.A.,
SpicerC.G.1949; A method of estimating streptomycin in serum and other body fluids by diffusion through agar enclosed in glass tubes. J. gen. Microbiol. 3:184