Next we shall take one fact from physics. We all hear of electricity and various other forces connected with it. What electricity is no one knows, but so far as it is known, it is a sort of motion. There are various other motions in the universe; what is the difference between them and electricity? Suppose this table moves — that the molecules which compose this table are moving in different directions; if they are all made to move in the same direction, it will be through electricity. Electric motion makes the molecules of a body move in the same direction. If all the air molecules in a room are made to move in the same direction, it will make a gigantic battery of electricity of the room. Another point from physiology we must remember, that the centre which regulates the respiratory system, the breathing system, has a sort of controlling action over the system of nerve currents.