It is evident that some of these disturbances are not enduring, but are only temporary and therefore are due to functional disturbances of the nervous system. Physicians often see hysterical patients suffering from intense pain that requires an injection of morphine, yet after a series of such incidents, the physician is able to give an injection of plain water and produce just as good an anodyne effect. In these cases some influence of the will is enough to correct the painful disturbances. Occasionally a single member loses sensation, or motion, or both, yet the fact that its nutrition does not suffer shows that there is only disturbance in the motor connections between it and the central nervous system and not in the sensory nor trophic tracts, and that this functional defect may be restored by some favorable influence. _Nerve Supply and Health_.--We know now that when a part of the body is cut off from its connections with the central nervous system, it begins at once to be lowered in vitality and gradually tends to dissolution. This will be true in spite of the fact that the circulation continues as actively as before. It is not necessary, indeed, that the nerve trunk to a part should be cut, if it is sufficiently compressed its function is stopped and various disturbances begin to appear in the vitality of the part which it supplies. A typical example is to be seen in certain fractures of the clavicle, where a fragment presses on one of the nerves leading to the arm. After a time pains develop in the arm, a burning feeling is noticed in the skin, which becomes shiny and cold and of distinctly lowered vitality. Even a slight injury to the arm will now produce a serious ulcerative condition. There are evidently important influences for life that flow down through the nerves from the central nervous system, quite as important in their way as the nutritional elements which flow through the blood. How these influences of the mind on the body are accomplished is a portion of that larger mystery of the influence of mind, or soul, or principle of life, on the material elements of which our body is composed. Why a man receives a shock of lightning or a charge of electricity at high voltage, and without a mark on his body or a change in any cell that we can make out, be dead, though he was living an instant before, is another of these mysteries too familiar for discussion. There is no change in the weight of the body, nothing physical has happened, but what was living matter with the power to accomplish the functions of living things is now simply dead material, unable to resist the invasion of saprophytic micro-organisms which will at once, {90} unhampered, proceed to tear it down, though the preceding moment resistive vitality was completely victorious. The mystery remains, but the mechanism of the influence can now at least be studied with much more satisfaction than was the case a few years ago.