Apethecary Zelana has been studying the beasts of Hellfire Peninsula in the field.  She wants a sample of the blood you gathered; with luck, she might discover what turned those Bonechewer bastards' skins red!$B$BZelana is at Reaver's Fall, southeast of Thrallmar.  Follow the road east and when you see a destroyed, green-glowing hunk of metal, you're there.  She has a camp set up behind the wyverns.