Edward Jenner, a practicing physician, probably owed his discovery of vaccination as a preventive of smallpox to two circumstances in his own life: he was born and lived in Gloucestershire, England, in dairying country, and had endured weeks in an old-time smallpox "inoculation stable" when he was a small child. He never forgot the horrible experience.Intrigued by the old dairying superstition that victims of the cattle disease, cowpox, would never thereafter catch smallpox, he resolved to investigate this belief, with an eye to working out an immunization method against the dreaded human disease.How for many years he doggedly persisted against prejudice, ill fortune, and ill will, and lived to see his hopes brilliantly fulfilled, makes a scientific story which is at the same time warm with human interest.