As already intimated, this book adopts the view that education is a process of forming habits in the brain. In the formation of habits there are several principles that must be observed. Accordingly we shall devote a chapter to the consideration of habits in general before discussing the specific habits involved in various kinds of study. Habit may be defined roughly as the tendency to act time after time in the same way. Thus defined, you see that the force of habit extends throughout the entire universe. It is a habit for the earth to revolve on its axis once every twenty-four hours and to encircle the sun once every year. When a pencil falls from your hand it has a habit of dropping to the floor. A piece of paper once folded tends to crease in the same place. These are examples of the force of habit in nonliving matter. Living matter shows its power even more clearly. If you assume a petulant expression for some time, it gets fixed and the expression becomes habitual. The hair may be trained to lie this way or that. These are examples of habit in living tissue. But there is one particular form of living tissue which is most susceptible to habit; that is nerve tissue. Let us review briefly the facts which underlie this characteristic. In nerve tissue, impressibility, conductivity and modifiability are developed to a marked degree. The nerve-cells in the sense organs are impressed by stimulations from the outside world. The nervous current thus generated is conducted over long nerve fibers, through the spinal cord to the brain where it is received and we experience a sensation. Thence it pushes on, over association neurones in the brain to motor neurones, over which it passes down the spinal cord again to muscles, and ends in some movement. In the pathway which it traverses it leaves its impression, and, thereafter, when the first neurone is excited, the nervous current tends to take the same pathway and to end in the same movement.