"_On carefully observing the countenances of the two females it is evident that they involve an effort of the will. They evidently attempted to conceal any indications of voluntary effort, but did not succeed. A voluntary effort was manifested, and it was plain that it could not be continued very long without fatigue._ Assuming, then, this _positive fact_, the inquiry arises, how can the will be exerted to produce sounds ('rappings') without obvious movements of the body? The voluntary muscles themselves are the only organs, save those which belong to the mind itself, over which volition can exercise any direct control. But contractions of the muscles do not, in the muscles themselves, occasion obvious sounds. The muscles, therefore, to develop audible vibrations, must act upon parts with which they are connected. Now, it was sufficiently clear that the 'rappings' were not _vocal_ sounds; these could not be produced without movements of the respiratory muscles, which would at once lead to detection. Hence, excluding vocal sounds, _the only possible source of the noises in question, produced as we have seen that they must be, by voluntary muscular contraction, is in one or more of the movable articulations of the skeleton_, from the anatomical construction of the voluntary muscles. This explanation remains as _the only alternative_. "By an analysis prosecuted in this manner we arrive at the conviction that the 'rappings,' assuming that they are not spiritual, _are produced by the action of the will, through voluntary action on the joints_. "Various facts may be cited to show that the motion of the joints, under certain circumstances, is adequate to produce the phenomena of the 'rappings.' * * * By a curious coincidence, after arriving at the above conclusion respecting the source of the sounds, _an instance has fallen under our observation, which demonstrates the fact that noises precisely identical with the spiritual 'rappings' may be produced in the knee-joints_." The doctors then describe how the sounds may be produced in certain subjects by the partial dislocation of the knee joint; and they add: "The visible vibrations of articles in the room, situated near the operator, occur if the limb, or any portion of the body, is _in contact with them_ at the time the sounds are produced. _The force of the semi-dislocation of the bone is sufficient to occasion distinct jarring of the doors, tables, etc., if in contact._ The intensity of the sound may be varied in proportion to the force of the muscular contractions, and this will render the apparent source of the 'rappings' more or less distinct." I have italicized the portions of these extracts which apply in a measure to the action of the toe-joints, as well as to that of the knee. No especial comment upon them is needed. The reader may easily comprehend the relation of these peculiar facts.