Abraham and Chain first announced the purification of penicillin, a critical step before production of the drug could begin, in a two paragraph paper published on a single page of Nature on March 21, 1942. The method, developed by biochemist Norman Heatley, extracted penicillin from huge volumes of filtrate coming offf the production line by extracting it into amyl acetate and then back into water, using a countercurrent system. Then Edward Abraham, another biochemist, used the newly discovered technique of alumina column chromatography to remove impurities from the pencillin prior to clinical trials. The authors wrote in their announcement, "The preparation thus obtained, though not crytalline has an activity of 450-500 Oxford penicillin units per mgm., corresponding to a complete inhibition of the growth of Staphylococcus aureus in broth in a dilution of 1: 25,000,000. Pencillin must therefore regarded as one of the most powerful antibacterial substances with predominantly bacteriostatic action known."