Polio vaccine is usually provided in vials containing 10–20 doses of vaccine. A single dose of oral polio vaccine (usually two drops) contains 1,000,000 infectious units of Sabin 1 (effective against PV1), 100,000 infectious units of the Sabin 2 strain, and 600,000 infectious units of Sabin 3. The vaccine contains small traces of antibiotics—neomycin and streptomycin—but does not contain preservatives. In a generic sense, vaccination works by priming the immune system with an 'immunogen'. Stimulating immune response, by use of an infectious agent, is known as immunization. The development of immunity to polio efficiently blocks person-to-person transmission of wild poliovirus, thereby protecting
David Bruce (microbiologist) tsetse fly vector, of African trypanosomiasis ("sleeping sickness"). He was Surgeon-General for the duration of the First World War from 1914–19 at the Royal Army Medical College, Millbank, London. "Brucella" is the genus and Brucellaceae is the family of the bacteria which was named after him, in recognition of his discoveries. "Brucella melitensis" is the cause of undulant fever in man and of abortion in goats. It is usually transmitted by goat's milk. "Trypanosoma brucei", the cause of sleeping sickness, is also named after him. Bruce was elected a Fellow of the Royal Society (FRS) in 1899. He served as