The scientist who discovered the chemical structure of hemin, the iron-laden compound in red blood cells that gives blood its color, was born on this day in 1881. Hans Fischer studied medicine and chemistry simultaneously, but decided to be an organic chemist rather than a doctor. Fischer tackled a problem that had stumped scientists for decades: how the oxygen, nitrogen, iron, and chlorine atoms in a hemin molecule are arranged. Having solved this mystery, Fischer began studying two other pigments: those in bile, and those in the chlorophyll that makes plants green. He found that their molecular structures were surprisingly similar to that of hemin. In 1930, Fischer was awarded the Nobel Prize in chemistry. He died 15 years later.