Question 10
In the later 1800s , the brilliant French chemist Louis Pasteur worked with chicken cholera , passing the disease agent from sick to healthy chickens . He suspended his research and went on vacation for several weeks . When he returned , the old cholera culture he gave to healthy chickens failed to kill them . He assumed his culture was bad and injected these same chickens with a fresh culture of chicken cholera . These chickens remained healthy while new chickens injected with the fresh culture of chicken cholera rapidly became sick and died . From our current knowledge of immunity , how would these observations be explained ?