Q28 What work is considered as a healthy maintenance system? A The immunity system and the self-restoration system have come to be alike of an important role in a healthy maintenance system. It is the structure corresponding to various accidents which happen by the cause of the exterior or an inside. Not only man but all living things have this system. In connection with evolution of a living thing, as for this system, updating procedure is taken continuously. The case in which a new type of the detrimental microbe appeared is supposed. There is also an individual which becomes extinct by it. But, a tolerant individual also appears and opposes. The weak race of an immunity system or a self-restoration system retreats from the center of biota by the law of natural selection.