Edward Jenner’s smallpox inoculation experiment was based on his observation that some dairymaids who worked with cows had suffered lesions on their hands, but that these dairymaids were immune to the more severe smallpox. Which best explains why the dairymaids were immune to smallpox?
Answer
A
They did not interact with many people so they were not exposed to the pathogen.
B
They frequently washed their hands so they were able to wash away the pathogen.
C
They were exposed to cowpox, and the substance their body produced to fight cowpox also attacked smallpox.
D
They breathed the air around the cows that carried an antipathogen in it that destroyed the pathogen.
Explanation
The dairymaids had been exposed to cowpox through lesions from infected cows. Their immune systems produced defenses against cowpox, and those defenses also recognized and attacked the closely related smallpox virus. This cross-protection explains why they were immune to smallpox; washing hands or breathing cow air would not create that specific immunity.
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