Who did Edward Jenner do a case study on to discover the link between cowpox and smallpox?

• A. Siblings
• B. Farmers
• C. Milkmaids
• D. Milkmen

Answer: (C)

The main idea here is that cowpox infection seemed to protect against smallpox, a clue Jenner pursued by looking at people who worked with cows. Milkmaids were the focus because they frequently caught cowpox from cows during milking, and this group appeared to be protected from smallpox. Jenner even used material from a milkmaid with cowpox—Sarah Nelmes—to inoculate a boy, and then showed that he did not develop smallpox after exposure. This direct case involving a milkmaid provided the pivotal link between cowpox and immunity to smallpox, leading to the development of the vaccination concept. The other groups don’t fit the historical source as precisely; the famous, cited case centers on a milkmaid, not siblings, farmers in general, or milkmen.