When the Oxford team of Ernst Chain and Norman Heatley had laboriously collected their first two grams of penicillin (probably no more than 2% pure!), Chain injected two normal mice with 1 g each of this preparation, and waited to see what would happen. The mice survived with no apparent ill effects. Their boss, Howard Florey, was furious at what he saw as a waste of good antibiotic. Why was this experiment important?