These telegraph wires, you will observe, are just like the nerves which branch out from your brain to the uttermost parts of your body. Along them comes all the information which your brain can receive from outside. Your brain decides what action you will take, and messages flash along the nerves to the muscles which set the various parts of your body in motion. If you think of the commander and his staff as the brain of the army, and of the telegraph, telephone, motor car, motor cycle, and aircraft as the nerves of the army, you will have a good idea of how hundreds of thousands of men are moved and controlled by one master mind. * * * * * Another important term which you continually meet with is the word _communications_. Every army moves forward from what is called its base--that is, the place where its ammunition, food, and general supplies are stored. These stores must be continually brought up to the army as it needs them; otherwise it would starve. There must, then, be a speedy and safe road or system of roads and railways between the army and its base. As the army advances this _line of communications_ becomes longer and longer. It must be kept safe from the attacks of the enemy: for if a part of it between the _base_ and the _army_ were to be captured, the army would be cut off from its food and stores; and if it could not find a new line of communication, it would very soon be forced to surrender. Large numbers of soldiers are required to guard these lines of communications. You may think of them as the air-tube which supplies a diver with air. If by any means the air-tube should be cut or stopped up, the diver must immediately come to the surface, or perish. Along the lines of communication there is a constant coming and going. Food, ammunition, general supplies, and new bodies of men are continually passing from the base to the front, and the wounded and the empty trains are continually being moved from the front to the base. When an army so spreads out that it has a wide front, it must have several parallel lines of communication, so as to keep itself supplied with the necessities of war. So vastly important are these lines of communication that the opposing generals strive to cut them, and by so doing deprive their enemy of his supplies of food and ammunition. Another important way in which a general seeks to overcome his enemy is by breaking through the line opposed to him in one or more places. If he succeeds in doing this, he has no longer a strong, united force opposed to him, but two or more fragments which he can overcome separately with his own united and unbroken force.