On the Movement of Animals, Part Two

PROPOS. VIII.

Muscles are not contracted by vital motion through desiccation or an alteration similar to that which occurs in singed hair.

Chap. 1. Concerning the modes and mechanical operations by which the contraction of muscles can occur.

There is no lack of other modes in nature by which filaments are contracted and shortened. For we see that hair, bristles, nervous and tendinous fibers, intestines, skins, and all membranes are corrugated and shortened by the heat of fire; indeed, the very fibers of muscles themselves, when roasted and singed, are evidently contracted. Hence some suspect that the muscles of an animal could be contracted and shortened at its will in a similar way. We shall show, however, that this is entirely improbable and absurd. First, because these operations are performed by fire drying and burning, insofar as it draws out the fluid and slippery parts from the aforementioned glutinous substances, on account of the lack of which the remaining tenacious parts are united and bind themselves mutually, and hence the diminution of their mass and their contraction follows, as happens in clay and innumerable similar bodies. But in our case, such an operation has no place; for no desiccation or combustion is effected in the muscles when they are violently contracted. But if they say that dryness and combustion are not required for nerves and tendons to contract, but a simple heating alteration is sufficient—for in boiling water, boiled muscles are greatly shortened, even though they are always moist—

I answer them that, in truth, in boiled nerves and tendons, their internal parts have been made closer to one another and more solid, and constipated due to the expulsion