Friday, September 27, 2013

Hermann von Helmholtz, Biological Physicist

Who was the greatest biological physicist ever? That’s a difficult question, but one candidate is the German scientist Hermann von Helmholtz (1821-1894). Helmholtz was both a physician and physicist who made important contributions to physiology. Russ Hobbie and I mention him briefly in the 4th edition of Intermediate Physics for Medicine and Biology. In Chapter 6 on Impulses in Nerve and Muscle Cells, we write
“The action potential was first measured by Helmholtz around 1850”
That is true, but he made many other contributions to biological physics. To highlight some of these, I turn to Asimov’s Biographical Encyclopedia of Science and Technology. Asimov first describes Helmholtz’s work on vision (some of which I have described previously in this blog).
“Like [Thomas] Young, Helmholtz made a close study of the function of the eye, and in 1851 he invented an ophthalmoscope, with which one could peer into the eye’s interior—an instrument without which the modern eye specialist would be all but helpless…In addition he revived Young’s theory of three-color vision and expanded it, so that it is now known as the Young-Helmholtz theory.”
He also studied sound, the ear, and music (he was a fine musician).
“Helmholtz studied that other sense organ, the ear, as well. He advanced the theory that the ear detected differences in pitch through the action of the cochlea, a spiral organ in the inner ear. It contained, he explained, a series of progressively smaller resonators, each of which responded to a sound wave of progressively higher frequency. The pitch we detected depended on which resonator responded.”
And as Russ and I noted, he made pioneering measurements in nerve electrophysiology.
“Helmholtz was the first to measure the speed of the nerve impulse. His teacher, Muller, was fond of presenting this as an example of something science could never accomplish because the impulse moved so quickly over so short a path. In 1852, however, Helmholtz stimulated a nerve connected to a frog muscle, stimulating it first near the muscle, then farther away. He managed to measure the added time required for the muscle to respond in the latter case.”
He also helped formulate the principle of the conservation of energy, an idea he came upon when studying the behavior of muscle.
“But he is best known for his contributions to physics and in particular for his treatment of the conservation of energy, something to which he was led by his studies of muscle action. He was the first to show that animal heat was produced chiefly by contracting muscle and that an acid—which we now know to be lactic acid—was formed in the working muscle.”
Given my admiration for 19th century physicists, I’m a little surprised that I don’t know more about Helmholtz. This is probably because I am more familiar with the great British physicists—Faraday, Maxwell, Kelvin—than with the Germans of that era (this is odd, given that I am half German). I would not go so far as to claim Helmholtz was as great a physicist as my Victorian heroes, but I do suggest that he was a greater biological physicist. In fact, I think a good argument could be made that he is the greatest of all biological physicists.

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