=Habit and Nervous Action.=--The general flow of the nervous energy during such processes as the above, in which there is an interchange between conscious and habitual control, may be illustrated by the following figures. In these figures the heavy lines indicate the process actually going on, while the broken lines indicate that although such nerve courses are established, they are not being brought into active operation in the particular case. [Illustration: FIG. 1, FIG. 2, FIG. 3 A. Sensory Stimulus B. Lower Sensory Centre C. Higher Sensory Centre A' Higher Motor Centre B' Lower Motor Centre C' Motor Response] The arrows in Figure 1 indicate the course of sensory stimulation and motor response during the first efforts to acquire skill in any movement. No connections are yet set up between lower centres and the acts are under conscious control. The arrows in Figure 2 indicate the course of sensory stimulus and motor response in an ordinary habitual act, as when an expert fingers the piano keys or controls a bicycle while his mind is occupied with other matters. The arrows in Figure 3 indicate how, even in performing what is ordinarily an habitual act, the mind may at any time assume control of the movement. This is illustrated in the case of a person who, when unconsciously directing his bicycle along the road, comes to a narrow plank over a culvert. Hereupon full attention may be given to the movements, that is, the acts may come under conscious control. FORMATION OF HABITS It is evident from the nature of the structure and properties of the nervous system, that man cannot possibly avoid the formation of habits. Any act once performed will not only leave an indelible trace within the nervous system, but will also set up in the system a tendency to repeat the act. It is this fact that always makes the first false step exceedingly dangerous. Moreover, every repetition further breaks down the present resistance and, therefore, in a sense further enslaves the individual to that mode of action. The word poorly articulated for the first time, the letter incorrectly formed, the impatient shrug of the shoulder--these set up their various tracks, create a tendency, and soon, through the establishment of lower connections, become unconscious habits. Thus it is that every one soon becomes a bundle of habits.