As early as 1959, physics Nobel Prize winner Feynman once said that he had a fantasy that if we could swallow a surgeon, then many complex operations could be made very interesting and simple.
At the time, it was just an idea for him and he wanted to leave it to us to make it happen. Ten years later, in 1966, the Americans made a movie about it.
The story is about a Soviet scientist who escapes to the United States and is dying because his brain vessels have been damaged by spies. Then they came up with a way to shrink five doctors down to one part in a million and inject them into the blood vessels of Soviet scientists.
The five surgeons went through a series of adventures in his body, fighting the monster to upgrade, and finally found the bleeding point, successfully saving the life of the scientist. It sounds like a feature of the Cold War, but Cold War movies are all about the most high-tech things, and it was at that time that the concept of microdoctors in the body was first promoted to the general public.