Dr. Alexander Fleming's1 interest in leukocytic and antiseptic action on bacteria during the period from 1914 to 1918 and his work on variations of staphylococcic colonies led to observations of bacterial lysis in areas of colonies of a mold. He constantly sought information on bacterial inhibition and thus began his pursuit of this phenomenon. This particular mold belonged to the genus Penicillium and was identified as Penicillium notatum, the active substance of which he called penicillin.
Garrod2 described the extract of a mass culture of P. notatum as harmless to the mammalian body even though a thousand-fold the concentration necessary for therapeutic use was involved. Penicillin is unstable, and its salts of sodium and calcium are mainly in use. Its potency is expressed in terms of the Oxford unit, which is an arbitrary amount determined by a standard preparation, or the smallest amount of penicillin which when dissolved in 50
BERGER I. PENICILLIN IN OTOLARYNGOLOGIC PRACTICE. Arch Otolaryngol. 1946;43(1):19–21. doi:10.1001/archotol.1946.00680050029004