Francis Peyton Rous discovers a virus that can cause cancer in chickens. In 1909, a farmer brought Rous a hen that had a breast tumor. Rous performed an autopsy, extracted tumor cells and injected them into other hens, which subsequently developed tumors. This is the first experimental proof of an infectious etiologic agent of cancer. Rous is awarded the Nobel Prize in Medicine or Physiology in 1966.

Paul Ehrlich announces the discovery of an effective cure (Salvarsan) for syphilis, the first specific chemotherapeutic agent for a bacterial disease. Ehrlich was seeking an arsenic derivative and finally the 606th compound worked. He brought news of the treatment to London, where Alexander Fleming became one of the few physicians to administer it.

Frederick Twort announces the first discovery of bacteriophages, or bacteria-infecting viruses. Twort’s discovery was something of an accident. He had spent several years growing viruses and noticed that the bacteria infecting his plates became transparent, indicating that they had been lysed or broken open and destroyed. Felix d’Herrelle independently describes bacterial viruses and coins the term “bacteriophage.”

Albert Jan Kluyver and Hendrick Jean Louis Donker propose a universal model for metabolic events in cells based on a transfer of hydrogen atoms. The model applies to aerobic and anaerobic organisms.

Frederick Griffith discovers transformation in bacteria and establishes the foundation of molecular genetics. He shows that injecting mice with a mixture of live, avirulent, rough Streptococcus pneumoniae Type I and heat-killed, virulent smooth S. pneumoniae Type II, leads to the death of the mice. Live, virulent, smooth S. pneumoniae Type II are isolated from the dead mice.

Alexander Fleming publishes the first paper describing penicillin and its effect on gram-positive microorganisms. This finding is unique since it is a rare example of bacterial lysis and not just microbial antagonism brought on by the mold Penicillium. Fleming kept his cultures 2-3 weeks before discarding them. When he looked at one set he noticed that the bacteria seemed to be dissolving and the mold was contaminating the culture. When penicillin is finally produced in major quantities in the 1940s, its power and availability effectively launch the “Antibiotics Era,” a major revolution in public health and medicine. With Florey and Chain, Fleming is awarded the Nobel Prize in Medicine or Physiology in 1945