John Carreyrou

The first commercial spectrophotometer was developed in 1941 by the American chemist Arnold Beckman, founder of the lab equipment maker Beckman Coulter. It works by beaming rays of colored light through a blood

sample and measuring how much of the light the sample absorbs. The concentration of a molecule in the blood is then inferred from the level of light absorption. Spectrophotometers are used to measure substances like cholesterol, glucose, and hemoglobin. Cytometry, a way of counting blood cells, was invented in the nineteenth century. It’s used to diagnose anemia and blood cancers, among other disorders.