Leveling rifles for Boehl's camera is a company of the Seventh Regiment, U.S. Volunteers, a unit authorized by Congress. Idea was to enlist recruits in Missouri and southern states where yellow fever had been severe. Theory was they were immune to disease, which was claiming more lives than guns. The 7th was recruited among Negroes in Missouri and neighboring states for what might very well have turned out to be a deadly assignment, five years prior to Dr. Walter Reed's discovery of the yellow fever cycle.