Koch's postulates
Pasteur had highlighted a new threat—microorganisms benign to humans passing among and multiplying in nonhuman animals while gaining new virulence for humans—that is thought to loom and to have approximately materialized with AIDS. Although Koch's postulates are often inapplicable, they remain heuristic, and the authority of "fulfilling Koch's postulates" is still invoked in medical science, though often in modified form, as in the identification of HIV-1 as the cause of AIDS or the identification of SARS coronavirus as the cause of SARS.