American-Canadian anatomist Robert R. Bensley (1867–1956) and American anatomist Normand Louis Hoerr (1902–1958) disrupted the liver cells in a guinea pig and isolated mitochondria in 1934. Between 1938 and 1946, Albert Claude (1899–1983) continued the work of Bensley and Hoerr and isolated two fractions—a heavier fraction consisting of mitochondria and another fraction of lighter submicroscopic granules, which he called microsomes. Further developments led to the development of centrifugal techniques of cell fractionation commonly used now. The development of this procedure was one of the earliest examples of differential centrifugation. It initiated the era of modern experimental cell biology.

Centrifugation is the separation of immiscible liquids or solids from liquids by applying centrifugal force. Since the centrifugal force can be very great, it speeds the process of separating these liquids instead of relying on gravity. Biologists primarily use centrifugation to isolate and determine the biological properties and functions of subcellular organelles and large molecules. They study the effects of centrifugal forces on cells, developing embryos, and protozoa, thus allowing scientists to determine certain properties about cells, including surface tension, relative viscosity of the cytoplasm, and the spatial and functional interrelationship of cell organelles when redistributed in intact cells. (For more about cells, see the chapter “Cellular Basics.”)