On the Movement of Animals, Part Two

PROPOS. XII.

The vital contraction of a muscle does not occur through the corrugation of fibers, as it appears in earthworms.

Those who are suddenly moved by appearances without prior examination are often deceived; not indeed because experiences are not useful for acquiring knowledge, but because the experiences themselves are either not exact due to the imperfection of the senses, which cannot discern the smallest differences of things; or because the sense, without the criterion of reason, is often fallacious.

This happens in earthworms, which seem to be moved through the corrugation or bending of their long body into the most minute folds following one another alternately. And because it is accepted that the movement of animals does not occur except through the action of muscles, one could be persuaded here that the fibers of all muscles are contracted through a similar corrugation, like the coils of serpents.

Truly, because the mechanical doctrine and reason itself sufficiently declare the absurdity of the aforementioned corrugation in the fibers of muscles, we are plainly persuaded that muscles do not contract by corrugating themselves, neither in earthworms nor in other animals.

a Tab. 15. Fig. 6.

This is deduced from the three preceding lemmas, in which it was shown that to effect the complete corrugation GDCE of the rope AB, two powers, S and R, are required, which pull the ropes to opposite parts, namely S upward and R downward, and the forces of both are quadruple of the resistance of the weight