And Campbell's most famous story, "Who Goes There?", which was made into "The Thing" in the 1950's and again in the 1980's. The 1980's version was closer to the original story, although Campbell's story is even more "out there". Worth reading.
Not sure of the copyright, but this site has had it posted for about three years:
http://www.scaryforkids.com/who-goes...hn-w-campbell/