The antibacterial properties of the sulfonamides were discovered in the mid-1930s following an incorrect
hypothesis but after observing the results carefully and drawing correct conclusions. Prontosil rubrum, a red
dye, was one of a series of dyes examined by Gerhard Domagk of Bayer of Germany in the belief that it
might be taken up selectively by certain pathogenic bacteria and not by human cells, in a manner analogous
to the way in which the Gram stain works, and, therefore, serve as a selective poison to kill these cells. The
dye, indeed, proved to be active in vivo against streptococcal infections in mice. Curiously, it was not active
in vitro.
