Answer:
vaccine
Step-by-step explanation:
British physician and biologist Edward Jenner was born in Berkeley, County Gloucestershire on May 17, 1749. He was the fourth son of Reverend Jenner, vicar of Berkeley.
At that time, smallpox was a very feared infectious plague that whipped Europe and America fundamentally, and for which there was no treatment or way to prevent it. It was caused by the Variola virus, although at that time it was not known.
Jenner observed that cows suffered from a disease called Vaccina or cowpox, which causes rashes in udders similar to those produced by human smallpox.
“He tested his vaccine with an 8 year old boy”
Sometimes they spread the disease to the milkmaids, in which pustules appeared on the hands. Fortunately, it was a benign condition and those affected soon recovered with very few sequelae.
But what really caught Jenner's attention was that these people became immune against human smallpox.