Apothecary Zelana at Reaver's Fall wants you to speak with Wing Commander Brack to take a wyvern to Spinebreaker Post, and then bring the Bleeding Hollow Blood Sample to Apothecary Albreck at Spinebreaker Post.
[player], my equipment here is, unfortunately, not configured for all the tests I'd like to perform. However, my colleague at Spinebreaker Post, Apothecary Albreck, possesses the required implements.
I have acquired a sample of bleeding hollow blood -- gained from a past mission of Thrallmar's agents. Take the sample to Albreck and allow him to study it.
To reach Spinebreaker Post, speak with Wing Commander Brack, near the wyverns to the south.