Penicillin nontoxic in humans by first performing toxicity tests in animals and then on humans. His subsequent experiments on penicillin's response to heat and pH allowed Fleming to increase the stability of the compound. The one test that modern scientists would find missing from his work was the test of penicillin on an infected animal, the results of which would likely have sparked great interest in penicillin and sped its development by almost a decade. The importance of his work has been recognized by the placement of an International Historic Chemical Landmark at the Alexander Fleming Laboratory Museum in London on
History of penicillin to concentrate the active substance involved, which he named penicillin, in 1928. Penicillin was the first modern antibiotic. During the next twelve years Fleming grew, distributed, and studied the original mold, which was determined to be a rare variant of "Penicillium notatum" (now "Penicillium chrysogenum"). Many later scientists were involved in the stabilization and mass production of penicillin and in the search for more productive strains of "Penicillium". Important contributors include Ernst Chain, Howard Florey, Norman Heatley, and Edward Abraham. Shortly after the discovery of penicillin, scientists found that some disease-causing pathogens display antibiotic resistance to penicillin. Research that aims