the same, though more complicated. The message is transmitted to the brain, where it is received by a cluster of small sensory cells or nerve-centres, which are connected with another cluster of fewer and larger motor-centres, often at some distance from them, by a network of interlacing fibres. But it is always a case of a single circuit of wires, batteries, and accumulators, adapted for receiving, recording, and transmitting one sort of vibrations caused by and producing one sort of energy, and one only. The brain does not act as a whole, receiving indiscriminately impressions of light, sound, and heat; but by separate organs for each, located in separate parts of it. It is like a great central office, in one room of which you have a printing instrument reading off and recording messages sent through an electric telegraph; in another a telephone; in a third a self-registering thermometer, and so on. And the same for the motor-centres and nerves. One set is told off to move the muscles of the face, another those of the arms, others for the legs and body, and so forth. This is further complicated by the fact that the brain like the rest of the body has two sides, a right and left, and that in some cases the motor-apparatus is doubled, each working only on one side, while in others the same battery and wires serve for both. As a rule the right hemisphere of the brain works the muscles of the left side of the body, and _vice versâ_, so that an injury to one side of the brain may paralyse the voluntary motion of the limbs on the opposite side, leaving in a perfect condition those on its own side.