A portrait of the scientist as a young man

1- The microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms.

2-The microorganism must be isolated from a diseased organism and grown in pure culture.

3- The cultured microorganism should cause disease when introduced into a healthy organism.

4- The microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.