How horrific was yellow fever in Texas? Between 1839 and 1867, Galveston was hit by no fewer than nine epidemics of this terrible disease. One of the worst came in 1853, when roughly six out of every ten Galvestonians fell ill and more than 500 died --- roughly one in ten residents. Think of how grim it must have been living in such a place and not knowing exactly what the source of the killer is. For decades, doctors believed yellow fever spread through contaminated air, rotting vegetation, sewage, or contact with infected people. Nobody understood that the real culprit was a mosquito. Walter Reed solved the puzzle in 1903. The last major outbreak was in New Orleans in 1905, when 400 people died. Shown here: Galveston in 1910