Attention, Earthlings! This is Captain Blastoff, coming to you from a gallery in the future, talking about the great popular art form of the past: Cheap Science Fiction Paperback Book Covers!
This posting I present: From Outer Space (previously The Needle) by Hal Clement, Avon 1950
Cover artist uncredited. (boo!) But the art tells the story well:
Two rockets crash in the ocean near an island. From one comes a detective amoeba from outer space who takes up residence inside a boy by sending tentacles throughout his body. Why? Because he’s chasing a criminal amoeba from outer space who is hiding in some other earthling, of course!
A lot of the fun comes from two life forms sharing the same body. For instance, “Hunter,” the detective amoeba, gets rid of other animals in the boy’s body, like viruses and germs. I guess it wouldn’t be so bad having an “inner doctor,” huh? But the whole idea of an intelligent jelly-alien inside my bod’ makes me feel kind’a squirmy.
The amoeba’s tentacles communicates to the boy by enlarging blood vessels on the inside of his eyes to write messages he then sees “written in the air!” They call this “inner net.”
Just kidding! (About the “inner net” part. The method of communication really is part of the book, believe it or not.)
This has been Captain Blastoff, ending transmission.