On the Movement of Animals, Part Two (1681) - Page 20

out boiling, without singeing or hardness, and without any persistent alteration and commutation of the bodily substance of the muscles, but rather from a certain motive and pain-perceiving force: as is evident in the aforementioned removed heart, a little after its rest and torpor, when it appears extinct, if it is pricked with a needle or irritated with an acrid juice, it suddenly revives and reassumes its omitted pulsations.

Next, it must be seen whether muscles can be contracted through the corrugation of the fibers; for the investigation of which, the following Lemmas are premised.

PROPOS. IX.

a Tab. 15. Fig. 5.

If a cord AB , affixed to a nail X, is tensed by a weight Z suspended at B, and the intermediate part is twisted by the powers R and S, and is corrugated in the same plane, so that the cord remains tensed by four tractions, and the intermediate directions DO, IC are parallel to each other and bisect the alternate angles of the cord. I say that the powers S, R have the same proportion to the weight Z as the quadruple of the sine of the angle DGO (the complement of half the angle of the cord's flexion GDF) has to the total sine.

b Par. 1. pr. 69.

Let the cord DC be bisected at F, and let the line GFE be drawn perpendicular to DO, CI. Because power S, by pulling the cords DG, DF through the direction ODS, acts against two resistances of Z itself and of that which impedes the traction of point F toward D, and the directions DG, DF are equally inclined to the elevation OD, and the confluence D is movable through the direction OD: therefore