On the Reason of the Movement of the Muscles (review)

William Croone. On the Reason of the Movement of the Muscles. Translated by Paul Maquet. Introduction by Margaret Nayler. Transactions of the American Philosophical Society, vol. 90, part 1. Philadelphia: American Philosophical Society, 2000. 130 pp. Ill. $20.00 (paperbound, 0-87169-901-X).

William Croone (1633-84) was a physician-polymath, the first Register of the Royal Society, a practicing physician who occupied his mind with efforts to answer many interesting questions about nature. He was a rationalist who believed in experimentation. His name is remembered today largely as attached to two Croonian Lectures--one addressed to the Royal Society, the other to the College of Physicians--established by his will and funded by his wife's estate. During his lifetime there was considerable interest in the mystery of the mechanism by which muscles moved. What was tantalizing was that there were many organs whose function was unknown (the liver, for example), but here was a tissue, muscle, about whose function there was no doubt; yet no one understood how it was able to carry out that function.

Croone seized upon an idea that had been in the wind for several decades--perhaps beginning with an observation by Robert Boyle--that an animal bladder filled with air was able to push up a weight. John Wilkins reported a similar observation to the Royal Society in 1661, and suggested that the phenomenon might be a model for the mechanism of muscle movement. Croone's contribution was to formulate a specific hypothesis to explain the mechanism by which muscle caused movement about a joint. In 1664 he published anonymously, in Latin, a treatise De ratione motus musculorum. His hypothesis was that muscles, particularly the fleshy part (muscle fibers), were filled with fluid, injected into them by nerves--which themselves were at all times filled with a liquid, proposed to be formed by the filtration of blood in the brain, through brain tissues into nerves. This injection of liquid into muscle fibers caused swelling of the muscle belly, which was capable of lifting a weight. Croone studied various directions at which a fluid-swollen animal bladder exerted various forces, and from this proposed a geometric model of forces that such a muscle could exploit to, for example, flex an arm at the elbow.

The American Philosophical Society has just republished Croone's treatise, a facsimile of each page of the original Latin with an English translation on the facing page. The thirty-two pages of the Latin treatise are overmatched by a thoughtful, critical, and thorough introduction, by Margaret Nayler, that not only places Croone's hypothesis in the context of his times, but also extends its material to cover observations and hypotheses made by Croone and his contemporaries after 1664.

There are many faults with this hypothesis, but in 1664 it was plausible. Croone did not have the benefit of Galvani's discovery, a century later, that muscle contraction is caused by an electric current (Galvani retained the notion that nerves transported a fluid, but supposed that this fluid was what he called "animal electricity"). By chance, at the time I received this book for review I was reading The Elegant Universe (1999) by the physicist Brian Greene, a popular description and explanation of quantum mechanics and relativity, and of superstring theory, that is intended to eliminate the contradictions between the two. No one has seen this fundamental particle, the supposed string, which is held to be of the size of a quantum length (10^-33 cm). It seemed to me that the quality of intellectual activity brought to his hypothesis by Croone was no less than that of our modern physicists who ask us to accept a construct that at the moment appears to be beyond critical test of its possible uniqueness.

Croone's hypothesis was not beyond critical test even in his time. The hypothesis required that the volume of...