The power to perceive things present without the use of the ordinary organs, and to become aware of events happening at a distance, has been frequently ascribed to an additional sense, possibly the Common Sense of Aristotle. Its fainter operations are seen in the almost marvelous power possessed by bats to fly through minute meshes of silk nets, stretched out for the purpose, even when deprived of sight, and to find their way to their nests without a moment's hesitation. Cuvier ascribed this remarkable power to their exquisitely developed sense of touch, which would make them aware of an almost imperceptible pressure of the air; but while this might explain their avoiding walls and trees, it could not well apply to slender silk threads. Another familiar illustration is found in the perfectly amazing ability often possessed by blind, or blind and deaf persons, who distinguish visitors by means neither granted nor known to their more fortunate brethren. It is generally believed that in such cases the missing senses are supplied by a superior development of the remaining senses, but even this assertion has never yet been fully proved, nor if proved, would it supply a key to some of the almost marvelous achievements of blind people. This new or general sense seems only to awaken in exceptional cases and under peculiar circumstances. That it never shows itself in healthy life is due to the simple fact that its power is then obscured by the unceasing activity of the ordinary senses. A peculiar, and as yet unexplained feature of this power is the tendency to ascribe its results, not to the ordinary organs, but by a curious transposition to some other part of the body, so that persons in magnetic sleep believe, as the magnetizer may choose, that they see, or smell, or hear by means of the finger-tips, the pit of the stomach, the forehead, or even the back of the head. It is true that savants like Alfred Maury (_Revue des Deux Mondes_, 1860, t. 25) and Dr. Michéa ascribe these new powers only to an increased activity of the senses; but nothing is gained by this reasoning, as such an astounding increase of the irritability of the retina or the tympanum is as much of a magic phenomenon as the presumed new sense. The simple explanation is that it is not the eye which sees nor the ear which hears, but that images and sound-waves are carried by these organs to the great nervous centre, where we must look for the true source of all our perceptions. If in magnetic sleep the same images and waves can be conveyed by other means, the result will be precisely the same as if the patient was observing with open eyes and ears.