THEIR many friends on this side of the Atlantic will have been delighted to hear of the award of the Nobel Prize for Physiology and Medicine for 1944 to Dr. Joseph Erlanger, formerly professor of physiology at Washington University, St. Louis, and Dr. Herbert S. Gasser, director of the Rockefeller Institute, New York. The award recognizes a fundamental advance in the analysis of the nervous system. Nowadays, amplifiers and cathode ray oscillographs are part of the standard equipment of the neuro-physiologist; the passage of the waves of activity in the peripheral nerve fibres can be timed to the nearest ten thousandth of a second and followed through the networks of the central nervous system with the same accuracy. It is to Gasser and Erlanger that we owe the introduction of this precision. They were the first to make effective application of new electrical techniques, after the War of 1914–18. By 1922 their cathode ray records had shown an unexpected complexity in the 'action potential' of a nerve trunk, and soon after they were able to prove that this was due to different groups of nerve fibres conducting at different rates.