As a matter of fact, this is not the case, for if one of your arms should be amputated, you would still feel a tingling in the fingers of the amputated arm. Thus has arisen a superstition that leads many people to bury any part of the body lost in this way, thinking that they will never be entirely relieved of pain until the absent member is finally at rest. Of course, the fact is that you would only _seem_ to have feeling in the amputated arm. The sensation would really occur in the central brain tissue as the organ of the governing intelligence, the organ of consciousness. [Sidenote: _Laboratory Proof of Sense-Perceptive Process_] And you may set it down as an established principle that _all states of consciousness, whether seemingly localized on the surface of the body or not, are connected with the brain as the dominant center_. The facts we have been recounting have been established by the experiments of physiological psychology. Thus, the work of the laboratory has shown that between the moment when a sense vibration reaches the body and the moment when sensation occurs a measurable interval of time intervenes. If your eyes were to be blindfolded and your hand unexpectedly pricked with a white-hot needle, the time that would elapse before you could jerk your hand away could be readily measured in fractions of a second with appropriate instruments. [Sidenote: _Reaction Time_] This interval is known as _reaction-time_. It varies greatly with different persons. During this reaction-time, the cell or cells attacked upon the surface of the hand have conveyed news of the assault through numberless intermediate sensory nerve cells to the brain. The brain in turn has sent out its mandate through the appropriate motor nerve cells to all the muscle and other cells surrounding the injured cell, commanding them to remove it from the point of danger. The work of the nervous system in dealing with the ether vibrations that are constantly impinging upon the surface of the body has been likened to that of the transmitter, connecting wire and receiver of a telephone. Air-waves striking against the transmitter of the telephone awaken a similar vibratory movement in the transmitter itself. This movement is passed along the wire to the receiver, which vibrates responsively and imparts a corresponding wave-like motion to the air. [Sidenote: _The Human Telephone_] These air-waves when heard are what we call _sound_. In the same way, air-waves striking the ear are communicated by the auditory nerve to the brain, where they awaken a corresponding sensation of sound. But these waves must be vibrating at between 30 and 20,000 times a second. If they are vibrating so slowly or so rapidly as not to come within this range, we cannot hear them. [Sidenote: _The Living Telegraph_]