American physiologist, corecipient (with Joseph Erlanger (Erlanger, Joseph)) of the Nobel Prize for Physiology or Medicine in 1944 for fundamental discoveries concerning the functions of different kinds of nerve fibres (axon).

At Washington University, St. Louis, Mo. (1916–31), where he was professor of pharmacology, Gasser collaborated with Erlanger in studying the barely detectable electrical impulses carried by isolated mammalian nerve fibres. By 1924 they had succeeded in adapting the oscillograph to physiological research, enabling them to visualize amplified nerve impulses on a fluorescent screen. Using this device, they demonstrated that different nerve fibres exist for the transmission of specific kinds of impulses, such as those of pain, cold, or heat. Their work also made it possible to construct improved recording machines to diagnose brain and nervous disorders and to ascertain the success of treatments for these diseases.

In 1931 Gasser was appointed professor of physiology at Cornell University, Ithaca, N.Y., and four years later he succeeded Simon Flexner as director of the Rockefeller Institute, New York City (1935–53).