For years physiologists have been endeavoring to discover the nature of nerve impulses and many theories, more or less elaborate, have been advanced, only to fail of acceptance because of insufficient foundation on known facts. The idea that all other physiologic activities with which we are familiar are associated with, if not caused by, chemical changes has sustained most investigators in the belief that this function also would some day be explained on chemical grounds—and this in spite of the fact that neither thermal nor chemical changes have ever been shown in nerves as a result of physiologic activity, unless changes in electromotor responsiveness be considered evidence of a chemical change. While this argument ignores some of the slower physiologic processes, such as diffusion and osmosis, which arc of a distinctly physical nature, it may with some degree of fairness be applied to a phenomenon such as a nerve impulse.
THE NATURE OF NERVE IMPULSES.. JAMA. 1907;XLIX(19):1610. doi:10.1001/jama.1907.02530190044007