Story of Psychology - Morton Hunt [72]
Helmholtz, firmly opposed to this quasi-mystical view, wrote a paper titled “The Conservation of Force,” based on his frog data and his knowledge of physics, and presented it before the Berlin Physical Society in 1847. His thesis was that all machines obey the law of conservation of energy; therefore, perpetual motion is impossible. He then argued that this is true of organic processes, too, and that vital force, having no source of energy, would violate that law and hence did not exist. In short, he put physiology on a firmly Newtonian footing. The paper won him such respect that the Prussian government excused him from further military service, made him a lecturer on anatomy at the Berlin Academy of Arts, and a year later appointed him professor of physiology at the University of Königsberg.
For the next two decades, Helmholtz devoted himself largely to studies of the physiology of sensation and perception. (From then on, he concerned himself chiefly with physics, at the University of Berlin.)
His historic first research achievement was to measure the speed with which the nerve impulse travels along the nerve fiber. His mentor, Müller, like most other physiologists of the time, had taken Galvani’s discovery of the electrical nature of the nerve impulse to mean that the nervous system was somewhat like a set of continuous wires through which the current flowed at extremely high speed—roughly the speed of light, according to one reckoning. But Helmholtz’s friend Du Bois-Reymond had chemically analyzed nerve fibers and suggested that the impulse might be not purely electrical but electrochemical; if so, it would be relatively slow.
In his laboratory at Königsberg, Helmholtz undertook to measure the speed of the impulse in a frog’s motor nerve. Since the high-speed chronoscope was not yet generally available—the first one was then in development—he ingeniously rigged a galvanometer to a frog’s leg (with the motor nerve attached) in such a way that a needle drawing a line on a revolving drum would show the time elapsed between the instant a current was applied to the upper end of the nerve and the subsequent kick of the foot. Knowing the distance between stimulus and the foot muscle, Helmholtz could then calculate the speed of the nerve impulse; it proved to be remarkably slow, about ninety feet per second.
He also measured the speed of the nerve impulse in human subjects, asking volunteers to signal with a hand as soon as they felt a tiny current he applied either to toe or thigh. These experiments yielded figures ranging from 165 to 330 feet per second, but Helmholtz considered them less reliable than those based on the frog’s leg; something about the testing of humans made for wide variability.
At first his results, published in 1850, were not widely accepted; they were too hard to believe. Physiologists were still wedded to the notion that either immaterial animal spirits or electricity flowed through the nervous system, and Helmholtz’s data supported a different theory, namely, that the nerve impulse consisted of the complex movements of particles. Moreover, his findings contradicted common experience. We seem to feel a touch on finger or toe the instant the contact is made; we seem to move a finger or toe the instant we mean to.
Yet his evidence could not be gainsaid, and after initial resistance, his theory won general acceptance. Had he done nothing else, this alone would have made him one of the immortals of psychology, since it prepared the