Ugh, I said that wrong. I meant the realization that washing hands with soap is useful to prevent infections. Post Semmelweis.

That was a medical advancement. Part of modern medicine.

I'm pretty sure that counts as modern medical science. It's an early example, but the establishment of germ theory and being able to trace the vectors of disease of pretty fundamental to today's medical practices.

Yep, the doctor's dirty, unwashed hands (back then it was a 'mark of honor' to have bloody hands and apron) rooting around McKinley's abdomen to find the bullet was what killed him. He might well have lived if the dr's left him alone.