Question

1. When a mouse was injected with the rough strain of pneumonia, it lived.
2. When a mouse was injected with the smooth strain of pneumonia, it died.
3. When a mouse was injected with heat-killed smooth strain, it lived.
4. When a mouse was injected with a mix of the rough and heat-killed smooth strains, it died.

What can I conclude from the first 2 statements?
What can I conclude from the 3rd statement?
What can I conclude from the 4th statement?