MEN of science will welcome the announcement that the Nobel Prize for Medicine for 1945 has been awarded jointly to Sir Alexander Fleming, Sir Howard Florey and Dr. E. Chain. Sir Alexander Fleming is now professor of bacteriology in St. Mary's Hospital Medical School, London. During the First World War, when he was working upon the bacteriology of septic wounds, Fleming became convinced that the chemical antiseptics then in use were often very harmful to the leucocytes which attack bacteria, and he discovered, in 1922, lysozyme, an antibacterial ferment which occurs in many animal tissues and secretions. In 1924 he showed that, if the antileucocytic power of an antiseptic is greater than its antibacterial power, it is not likely to be therapeutically valuable. When, therefore, he published in 1929, six years before the announcement by Domagk of the discovery of the sulphonamides, the discovery of penicillin and an account of his early trials of its antibacterial action, it was evident that he had provided us with an antibacterial agent which was not only powerfully antibacterial against some of the most pathogenic of organisms, but was also not toxic to the all-important antibacterial leucocytes and also not toxic to the animal infected with them. Attempts made at that time, however, to extract a form of penicillin which could be used therapeutically were not successful, and it seemed that this remarkable antibacterial agent would be denied to man.