That the voluntary muscles are controlled by the central nervous mechanism needs no proof beyond the appeal to our personal experiences of every moment. You desire some object that lies on the table in front of you, and immediately your hand, thanks to the elaborate muscular mechanism, reaches out and grasps it. And this act is but typical of the thousand activities that make up our every-day life. Everyone is aware that the channel of communication between the brain and the muscular system is found in a system of nerves, which it is natural now-a-days to liken to a system of telegraph wires. We speak of the impulse generated in the brain as being transmitted along the nerves to the muscle, causing that to contract. We are even able to measure the speed of transfer of such an impulse. It is found to move with relative slowness, compassing only about one hundred and twelve feet per second, being in this regard very unlike the electric current with which it is so often compared. But the precise nature of this impulse is unknown. Its effect, however, is made tangible in the muscular contraction which it is its sole purpose to produce. The essential influence of the nerve impulse in the transaction is easily demonstrable; for if the nerve cord is severed, as often happens in accidents, the muscle supplied by that nerve immediately loses its power of voluntary contraction. It becomes paralyzed, as the saying is. THE NATURE OF MUSCULAR ACTION Paying heed, now, to the muscle itself, it must be freely admitted that, in the last analysis, the activities of the substance are as mysterious and as inexplicable as are those involved in the nervous mechanism. It is easy to demonstrate that what we have just spoken of as a muscle fibre consists in reality of a little tube of liquid protoplasm, and that the change in shape of this protoplasm constitutes the contraction of which we are all along speaking. But just what molecular and atomic changes are involved in this change of form of the protoplasm, we cannot say. We know that the power to contract is the one universal attribute of living protoplasm. This power is equally wonderful and equally inexplicable, whether manifested in the case of the muscle cell or in the case of such a formless single-celled creature as the amoeba. When we know more of molecular and atomic force, we may perhaps be able to form a mental picture of what goes on in the structure of protoplasm when it thus changes the shape of its mass. Until then, we must be content to accept the fact as being the vital one upon which all the movements of animate creatures depend.