This will be only for a time, however, for the additional strain will slowly but surely have a bad effect on the rest of the engine, and through it on the other parts of the machine. One by one these will give way, and have to be compensated in turn. If still neglected and left to take care of itself, there will come a time when so many sections are affected, that the remainder cannot overcome the mischief, and compensation will fail. The car will become practically useless. Perhaps, like the one-hoss shay, it will collapse _en masse_. It has gone beyond the stage of running badly, it has broken down. [Sidenote: The human machine.] The human system is much like a motor-car, in that it consists of a vast number of parts acting in unison. Yet it is infinitely more wonderful, for it is much more complicated, and can create its own supply of energy. It is made, roughly speaking, of a framework of bone and muscle, a delicately-adjusted alimentary system, whereby it takes in and assimilates food, and of a circulatory apparatus which drives blood and nourishment to all parts of the body. It contains also a nervous system, compared with which these other parts are crude, mechanical contrivances. For it is on their nervous supply that they depend for their usefulness. Cut the nerves that go to a limb, and the finest muscles in the world are as helpless as the meat in a butcher’s shop. Deprive the heart of its nerve supply for a single minute, and it will never beat again. Yet we pay vastly more attention to a weak heart, as it is called, or still more so to a broken leg, than we do to a threatened failure in the nervous system, which outweighs them all in importance. Once that has got out of order, the driving power is gone. Not only the heart and muscles, but every other faculty we possess loses its energy and usefulness. So closely allied, however, are the different parts, that the nervous system itself, which governs all else, is dependent for its welfare on the very organs it governs. Like the power of a king, it rests not only on its own intrinsic qualities, but also on the strength and harmony of the units over which it rules. [Sidenote: Interplay.] And there is a constant interplay going on between the various parts of the body. No one organ or system can stand alone. If it is working badly, it affects other parts, and disturbs the harmony on which the health of the whole depends. One of the most marked examples of this is to be found in the action and reaction which take place between the digestive organs and the nervous system. The presence of congenial company at meal-times is one of the best aids to digestion; a cantankerous discussion is the very opposite. Similarly, if a man sits down to his dinner with a grievance or a worry on his mind, it is safe to predict dyspepsia.