(Solved): French scientists Alexandre Yersin and Emile Roux were working to determine the causative agent of ...

French scientists Alexandre Yersin and Emile Roux were working to determine the causative agent of the disease diphtheria. They took tissue samples from infected animals, ground up the tissue, and then filtered the ground up mixture through a porcelein filter that had holes too small for bacteria to pass through (see picture below). This separated the ground up tissue into two parts: part 1) material that stayed on top of the filter, and part 2) material that passed through the filter into a flask. Yersin and Roux then introduced material from the two different areas into animals to see if they could reproduce the signs and symptoms of diphtheria in the animals. In other words, they had two groups of animals: one group that was inoculated with material from on top of the filter and one group that was inoculated with material that passed through the filter. The scientists found that the animals that were inoculated with material that passed through the filter developed the signs and symptoms of diphtheria. Which of the following would likely be a controlled variable in the experiment? Which part of the tissue sample (Part 1 or Part 2) they used to inoculate the animal The type and age of the animals they inoculated Whether or not the animal developed diptheria