Microbe

In Microbe: The Anatomical Adventure, published by Synergistic Software, the games manual states:

"You command the crew of the submarine Microbe, which has been shrunk to microscopic size and injected into the human body. Perhaps a blood clot in the brain threatens your patient's life. Find a way through the maze-like lungs, liver, heart, etcc, and fight off bacteria, funcgi, parasties, viruses, body defenses, and more!"