At first, then, most people will find it necessary to do something in order to attract their attention and guide their thoughts to something quite different from the forbidden subject. Later on, however, when they become more advanced in the science of right thinking, they will be able to direct their thoughts into any desired direction. This necessitates constant vigilance. Each thought has to be carefully scrutinized before being allowed to pass the threshold of the mind. By reversing every negative or unworthy or ignoble thought into its opposite, a change is wrought in the brain and nervous system. The cells formerly used for wrong thinking and for the production of wrong action go out of use as new cells are brought into use for the production of right action. This stage leads to one higher still, when it becomes a settled habit to reverse bad thoughts into good ones and perform right actions instead of bad or weak ones. The power of the sub-conscious mind, which at one time seemed so evil, produces right action more or less automatically. When once the habit of cleaning the teeth is established there is experienced an uncomfortable feeling until they have been attended to. When once a dirty person has learnt to wash himself thoroughly and keep himself decent, he will feel uncomfortable if he gets dirty. The same rule applies in the more important things and habits of life. If those who are in the bondage of habit will only direct their thoughts and attention to the building up of good habits, their old weaknesses will die a natural death.