Likely a sterile medium means an uncontaminated culture (food free of living organisms) that will grow only the new bacteria introduced for analysis. Source(s): http://www.thefreedictionary.com/sterile
Stonepelt was Bluestar's first mentor and a very well-respected senior warrior of ThunderClan. It is revealed in this book that he took her to the Gathering on her second day as an apprentice because she had caught a squirrel very well for a new apprentice, and the squirrel had been as big as she was.
Cat - Cats are aloof, cunning, graceful creatures. A cat-a-mountain (or wildcat) is one of the creatures turned into stone by the White Witch (LWW). One talking cat named Ginger is in league with the evil Calormenes and Shift the ape (who had the Narnians and the Calormenes believe that Aslan and Tash are one being).