I'm not sure there's just one. X-rays are interesting. I had never considered that. Consumption is no longer deadly with proper treatment Ah. And penicillin, which is apparently a very handy antibiotic. But the technology is a little beyond me. They can do minimally invasive surgeries with very small incisions and tools. There are ways to scan the brain and the body and monitor the heart.
It is quite a lot. Admittedly, I have been reading books on things that I found on the internet. If it seemed curious enough to read more about, I decided to do so.