Series of steps that must be taken to prove the cause of any infectious disease. Suspected causative agent must be found in every case of the disease...

Series of steps that must be taken to prove the cause of any infectious disease.

1. Suspected causative agent must be found in every case of the disease and be absent from healthy hosts. 

2. The agent must be isolated and grown outside the host. 

3. When the agent is introduced to a healthy, susceptible host, the host must get the disease. 

4. The same agent must be found in the diseased experimental host.