is performed by vibrations also. And conversely, if vibrations can be shown to take place in muscular motion, they must also be instrumental in sensation and intellectual perception.
Cor. II. There are certain experiments and observations which favour the supposition of the performance of muscular motion by subtle agitations in the small particles of the muscular fibres, i.e. by vibratory motions. It follows therefore, that these experiments and observations are some additional evidence for the existence of sensory and ideal vibrations, as above explained. Such are, that the motion of the heart, and of other muscles, may be renewed in dying animals, and those that are newly dead, by heat, injection of a fluid, and punctures, it being easy to be conceived, that the two last causes should put the particles of the fibres into agitations for a short time, i.e. till they can recover their equilibrium, by altering their distances, and mutual actions: and the first cause, i.e. heat, is, by the common consent of all, judged to consist in, and to cause, subtle vibratory motions. It is also difficult to assign any other action which these causes can have. In like manner, the alternate contractions and relaxations of the hearts of frogs, vipers, and some other animals, which continue for long spaces of time after these have been entirely separated from their bodies, seem utterly inexplicable upon any of the common suppositions, but follow easily from the doctrine of vibrations, as it is applied to muscular motion, in the two next propositions.
Cor. III. Since the same motion which occasions sensation, and intellectual perception, passes through the seats of these into the motory nerves, in order to excite there the automatic and voluntary motions, thus pervading the whole medullary substance, in various ways, according to the variety of the circumstances, but in all with the greatest precision and exactness; it follows, that this must be a vibratory one, and that of the most subtle kind. For the same excess of softness, which renders the medullary substance totally inelastic as to sense, and consequently unfit for the grosser vibrations of the particles of the first or largest order (by the vibrations of which, in sonorous bodies, it seems that sound is excited in the air), may render it more susceptible of vibrations, in the particles of the second, third, &c. orders; and if we suppose a proper ultimate structure in the several parts of the medullary substance, these vibrations may be conveyed with all that precision and variety which the phænomena require. And unless we do suppose some such subtle vibrations as these, it will be extremely difficult to conceive, how so soft a pulp as the medullary substance is, should be the common instrument of sensation, thought, and motion; which yet all physicians and philosophers must allow, according to the first and second propositions. If we set aside subtle vibratory motions, the impulse of the objects of sense can communicate nothing, as it seems, to so soft a
