The reference standard was a large batch of impure penicillin kept in Oxford. The assay was later modified by Floreys group to a more reproducible "cup assay": in this assay, a penicillin solution was defined to contain one unit/ml of penicillin when 339 microlitres of the solution placed in a "cup" on a plate of solid agar produced a 24 millimetre zone of inhibition of growth of Oxford Staphylococcus. : 107 
First International Standard (1944). A single 8 gram batch of pure crystalline penicillin G sodium was stored at The National Institute for Medical Research at Mill Hill in London (the International Standard). One penicillin unit was defined at 0.6 micrograms of the International Standard. An impure "working standard" was also defined and was available in much larger quantities distributed around the world: one unit of the working standard was 2.7 micrograms (the amount per unit was much larger because of the impurities). At the same time, the cup assay was refined, where instead of specifying a zone diameter of 24 mm, the zone size were instead plotted against a reference curve to provide a readout on potency. Second International Standard (1953). A single 30 gram batch of pure crystalline penicillin G sodium was obtained: this was also stored at Mill Hill. One penicillin unit was defined as 0.5988 micrograms of the Second International Standard.There is an older unit for penicillin V that is not equivalent to the current penicillin V unit.
Chemosensory data were also collected in a larger NHANES sample in 2013-2014. The prevalence of smell disorder (scores 0-5 out of 8 correct) was 13.5% in persons aged 40 years and over. If the same prevalence occurred in 2016, an estimated 20.5 million persons 40 and over had hyposmia or anosmia. In addition multiple demographic socioeconomic, and lifestyle characteristics were assessed as risk factors for diminished smell. In statistical analyses, greater age and male sex, coupled with either Black and/or non-Hispanic ethnicity, low family income, low educational attainment, high alcohol consumption (more than 4 drinks per day), and a history of asthma or cancer were independently associated with a greater prevalence of smell impairment. See also
Hyperosmia
Dysosmia
Anosmia


== References ==