a statement of the four steps providing evidence that a pathogenic microorganism is the cause of a disease. 1) The microorganism must be present in all cases of the disease. 2) It must be isolated from the diseased host and grown in pure culture. 3) This culture must reproduce the disease in a new host. 4) The microorganism must in turn be found and cultured from this new host. SYN: Koch law.
