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In the mid-nineteenth century Hermann von Helmholtz proved for the first time experimentally that nervous impulses are transmitted not directly by means of a "vital force" but at a finite, measurable velocity in the nerve tracts. Helmholtz's findings were a major step forward towards a comprehensive, scientific understanding of the specific nature of life processes. He demonstrated, for example, that life functions such as perception and desire, rather than being attributable to any vis vitalis, were the product of chemical and physical processes which could be quantified scientifically. Helmholtz's experiments were initially confined to frogs but later extended to human beings. His work on frogs has been published, unlike the results of the studies he undertook on human subjects. However, his first report - presented by his friend Emil du Bois-Reymond at a conference of the Physikalische Gesellschaft on 20 December 1850 - has survived as a draft in which Helmholtz gives a detailed description of this method. This document from the history of science is published here for the first time along with a brief introduction on its origin.