In the 1840s, a French pathologist in Paris, Gabriel Andral, looked down a microscope and found what two generations of microscopists had seemingly missed: yet another type of cell in blood. Unlike red blood cells, these cells lacked hemoglobin, possessed nuclei, and were irregularly shaped, occasionally with pseudopods—fingerlike extensions and projections. They were termed “leukocytes,” or white blood cells. (They are “white” only in the sense that they are not “red.”)
