The history of penicillin follows a number of observations and discoveries of apparent evidence of antibiotic activity of the mould Penicillium that led to the development of penicillins that became the most widely used antibiotics. Following the identification of Penicillium rubens as the source of the compound in 1928 and with the production of pure compound in 1942, penicillin became the first naturally derived antibiotic. There are anecdotes about ancient societies using moulds to treat infections, and in the following centuries many people observed the inhibition of bacterial growth by various moulds. However, it is unknown if the species involved were Penicillium species or if the antimicrobial substances produced were penicillin.