At the time, the medical profession was wrestling with emerging theories of inoculation. This simply involved injecting a dose of an actual disease, like a modern chickenpox party – where parents bring their toddlers together to deliberately pass the infection at an early age and infer immunity against later cases, which can have much more serious consequences. The early inoculators simply gave the full disease to patients when they were young and strong. They hopefully survived… and then would be immune.