An experiment of Billinies, since repeated with success by Doctor Monro, goes far to establish a positive effect exercised by the nerves in muscular motion. “After opening the thorax of a living dog, catch hold of, and press both the phrenic nerves with the fingers, the diaphragm ceases immediately to contract. Let go the hold of the nerves and the muscle acts again, pinch a second time the nerve or nerves, some way above the diaphragm, the muscle again ceases to act, keep firm hold of the nerves, with the fingers of the other hand strip or milch it down from the griping fingers towards the diaphragm, and the muscle is made to contract; and for three or four strippings or milchings, the action follows or obeys the motion of the fingers which strip it down, then it becomes disobedient and contracts no more, strip as you will, unless the finger, griping the nerves let go their hold and pinch farther up, when the muscle may again be made to contract, by stripping down towards the diaphragm.”――Also, an experiment performed by Dr. Whytt, in which he injected a strong solution of opium into the stomach and intestines of a living frog, after his heart was taken out; “in thirty minutes he appeared quite dead, and neither pricking or tearing its muscles produced any motion in them, or the members to which they were attached” but the doctor tells us, on irritating the spinal marrow with a probe, the limbs contracted feebly. Here there could have been no vis insita, or it would have evinced itself on the application of the mechanical stimulus to the muscles. And indeed the whole experiment rather serves to prove the entire dependence of the muscles for irritability on the nerves, for when rendered incapable of being excited, they were again brought into action by the remains of nervous energy, in the medulla oblongata, (called forth by the probe.) These considerations will I judge establish the direct influence of the nerves in muscular motion. And though its peculiar nature and qualities be unknown, an impenetrable veil shrouding it from observation, we may remain satisfied with a knowledge of the existence of an effectual cause. And as far as we may be allowed to infer from the general plans and regulations of nature surrounding us, seeing she delights in simplicity and uniformity, producing the greatest number of effects by the varied combination of a few elementary principles, we may rationally refer all the apparent complexness of the animal economy to the diversified influence of this nervous agent, particularly modified and applied to the variety of operations in the body, yet all tending to a unity of effect. And as simplification in our particular science appears the order of the day, I may be justified in supposing the irritability, sensibility, &c. of authors, but varieties in the action of this principle. Thus far we move with reason, beyond this point all is conjecture “and shadows, clouds and darkness rest upon it.”