In 1879 Pasteur observed that an aged culture of the fowl cholera bacterium had lost virulence but was still able to confer immunity against fresh strains. The finding, partly accidental, was turned by Pasteur into a deliberate methodological principle: the controlled attenuation of pathogens as a way to produce immunity without disease. It was the first time anyone had generalized Jenner's observation — specific to cowpox — into a method applicable in principle to any infectious disease. Pasteur explicitly paid tribute to Jenner by naming his procedure "vaccination," extending the term beyond smallpox.