1. Koch’s Investigation of Anthrax

2. Koch’s Experimental Step 1
Anthrax that was killing cows and sheep. Koch was curious about the cause of the disease.
Koch’s Experimental Step 1
In your science notebook, describe what Koch did in his first step.
Ask students what they think you would observe.

3. Koch’s Observation In your science notebook, record your observations.
Koch saw strange rod-like objects in the blood sample. He described some as “short and quivering.” Others were attached to form long, thin, thread-like structures.

4. What can you infer from the observations of sick and healthy cows?
Koch’s Experimental Step 2:
Koch’s Observation:
What can you infer from the observations of sick and healthy cows?
Record your inference in your science notebook.
Koch’s Experimental Step 2: He took the blood from a healthy cow that had been slaughtered for meat and placed it on a microscope slide.
Koch’s Observation: The blood did not contain the rods and threads that he had observed in the blood from the cow that died from anthrax.
NOTE: Normal blood will often contain white blood cells, which are the darker cells in the field of view.

5. Koch’s Inference: the “rods” and “threads” cause anthrax.
What would be the next experimental step?
Record the experimental step in your science notebook.

6. Koch’s Experimental Step 3:
Koch’s Observation:
What can you infer from this observation?
Record your inference in your science notebook.
Koch’s Experimental Step 3: Inject the tail of a healthy mouse with blood from a cow that died of anthrax. Put the mouse in a separate cage. Discuss the idea that Koch used a mouse because it was convenient for use in a laboratory. A mouse is an example of a model organism, which is an organism that is convenient for use in research in order to understand a biological process in other organisms.
Koch’s Observation: The next day, the mouse was dead.

7. Koch’s Inference: the mouse died of anthrax.
What would be the next experimental step?
Record the experimental step in your science notebook.

8. Koch’s Experimental Step 4:
tissue and blood from dead mouse spleen
Koch’s Observation:
What can you infer from this observation?
Record your inference in your science notebook.
Koch’s Experimental Step 4: After observing that the spleen was large and black when he dissected the mouse, Koch took a sample from the spleen and put in on a microscope slide. Explain to students that the spleen contains blood.

9. Koch’s Inference: the blood from the cow caused anthrax in the mouse.
What would be the next experimental step?
Record the experimental step in your science notebook.

10. Koch’s Experimental Step 5:
Blood from cow died from anthrax
Koch’s Observation:
Blood and tissue from
dead mouse spleen
What can you infer from this observation?
Record your inference in your science notebook.
Koch’s Experimental Step 5: Koch injected blood from sick cows dead from anthrax into healthy mice daily over the course of one month.
Koch’s Observation: Each day, the mouse was dead and bits of spleen tissue contained rods and threads. And, there were many more rods and threads than were seen in the drop of cow blood that was injected.

11. Koch’s Inference: the “rods” and “threads” are alive.
Koch’s Experimental Step 6:
After transferring one drop of culture to a new slide and letting it sit each day for 8 days, Koch had a purified culture.
What would be your next experimental step?
Record the experimental step in your science notebook.
Discuss why Koch would have inferred that the rods and threads were alive. Bring out the idea that they were reproducing and if they were reproducing they must be alive.

12. Koch’s Experimental Step 7:
Purified culture
from Step 6
What can you conclude about the cause of anthrax?
Record in your science notebook.