Given the task definition and input, reply with output. In this task, you're given passages that contain mentions of names of people, places, or things. Some of these mentions refer to the same person, place, or thing. Your job is to write questions that evaluate one's understanding of such references. Good questions are expected to link pronouns (she, her, him, his, their, etc.) or other mentions to people, places, or things to which they may refer. Do not ask questions that can be answered correctly without understanding the paragraph or having multiple answers. Avoid questions that do not link phrases referring to the same entity. For each of your questions, the answer should be one or more phrases in the paragraph, and it should be unambiguous.

Passage: During a Mardi Gras parade in New Orleans, a girl becomes the latest victim of the deadly virus "XB". Dr. Clinton Earnshaw has been following the outbreak but only is able to diagnose it. The federal government assigns him Jeff Adams, who has no medical or scientific training. Though Earnshaw is initially bemused by the assignment, Adams' value emerges when he remembers the 19th century discovery of a virus with similar characteristics. Known at the time as "Wood's Fever", it was discovered by Dr. Joshua P. Henderson. Both men know that Henderson's notes were destroyed in the 1871 Great Chicago Fire, his only remaining artifact a gold pocket watch. 
Adams introduces Earnshaw to a former NASA physicist and Nobel laureate, Dr. Amos Cummings, and his colleague Dr. Helen Sanders. The physicists have been experimenting with time travel and reveal their plan to send Earnshaw and Adams back in time to find Henderson's cure for Wood's Fever. After being outfitted with period gear, clothing, a small microscope and portable centrifuge, Earnshaw and Adams are briefed on the dangers of time travel. They step through a vault-like door into a room with a view of endless cloud-filled sky, and the process begins.
What virus was Clinton Earnshaw trying to find a cure for?