In the nineteenth century Robert Koch scientifically investigated the transmission of diseases. He proposed a procedure that would enable a person to determine if a specific microorganism caused a given disease. The first four steps of this procedure are listed below:
Microbes must be isolated from an infected host organism.
The isolated microbes are then grown in a pure culture.
The microbes from the pure culture are injected into a new host.
If the new host contracts the disease, the microbes must be isolated from the new host and grown in a new culture.

Question

In the nineteenth century Robert Koch scientifically investigated the transmission of diseases. He proposed a procedure that would enable a person to determine if a specific microorganism caused a given disease. The first four steps of this procedure are listed below:
Microbes must be isolated from an infected host organism.
The isolated microbes are then grown in a pure culture.
The microbes from the pure culture are injected into a new host.
If the new host contracts the disease, the microbes must be isolated from the new host and grown in a new culture.

anonymous · Answer

What final step should be taken to prove that these specific microbes cause the given disease?

anonymous · Answer

Mix the microbes from the new and old cultures.
Inject an organism immune to the disease with microbes from the new culture.
Inject diseased organisms with the microbes from the new culture.
Compare the original microbes with the microbes in the new culture.