There was a Golden Age of Microbiology, and then at the tail end of the 1800s, new fields of science related to microbiology were being born left and right.
After studying the propagation of diseases like cholera, a man named John Snow took it upon himself to sanitize a region of London that, at the time, was going through a cholera outbreak. He noticed that the water pump in the street was close to and possibly contaminated with human feces. He took the hand pump off and everyone was miffed that they had to travel further to get water, however, cholera rate decreased. He founded infection control and epidemiology.
Jenner is the father of vaccination. He noticed that milkmaids weren’t getting smallpox, like everyone else. He notices abrasions on the utters of cows and on the hands of the maids, leading him to the conclusion that the two were related. He exposed a child to the pus that was inside the abrasion on the cow’s utter and then to a smallpox-infected person. Normally, the child would have contracted smallpox from this exposure, however, he remained immune. This was the birth of virology and the invention of vaccines.
Gram’s discovery that stained bacteria could be differentiated by stains suggested to the German Biologist that chemicals could affect bacteria individually. And if this was true, he concluded, then maybe we could use certain chemicals to kill some bacteria in a system without harming others, like our own. He searched for a “Magic Bullet” by surveying an exhaustive amount of chemicals and pathogens. Though he never quite found this ‘bullet’, he did discover the chemical that worked actively against syphilis, although it is no longer used due to it’s toxicity to humans.