waking up some fine morning, to find himself one of the competent ones of his generation, in whatever pursuit he may have singled out."--JAMES, _Psychology_. Some Rules for Forming Good Habits.--Professor Horne gives several rules for making good or breaking bad habits. They are: "First, _act on every opportunity_. Second, _make a strong start_. Third, _allow no exception_. Fourth, _for the bad habit establish a good one_. Fifth, summoning all the man within, _use effort of will_." Why not try these out in forming some good habit? You will find them effective. [Illustration: The effect of fatigue on nerve cells. _a_, healthy brain cell; _b_, fatigued brain cell.] Necessity of Food, Fresh Air, and Rest.--The nerve cells, like all other cells in the body, are continually wasting away and being rebuilt. Oxidation of food material is more rapid when we do mental work. The cells of the brain, like muscle cells, are not only capable of fatigue, but show this in changes of form and of contents. _Food_ brought to them in the blood, plenty of _fresh air_, especially when engaged in active brain work, and _rest_ at proper times, are essential in keeping the nervous system in condition. One of the best methods of resting the brain cells is a change of occupation. Tennis, golf, baseball, and other outdoor sports combine muscular exercise with brain activity of a different sort from that of business or school work. But change of occupation will not rest exhausted neurones. For this, sleep is necessary. Especially is sleep an important factor in the health of the nervous system of growing children. Necessity of Sleep.--Most brain cells attain their growth early in life. Changes occur, however, until some time after the school age. Ten hours of sleep should be allowed for a child, and at least eight hours for an adult. At this time, only, do the brain cells have opportunity to rest and store food and energy for their working period. Sleep is one way in which all cells in the body, and particularly those of the nervous system, get their rest. The nervous system, by far the most delicate and hardest-worked set of tissues in the body, needs rest more than do other tissues, for its work directing the body only ends with sleep or unconsciousness. The afternoon nap, snatched by the brain worker, gives him renewed energy for his evening's work. It is not hard application to a task that wearies the brain; it is _continuous_ work without rest. THE SENSES Touch.--In animals having a hard outside covering, such as certain worms, insects, and crustaceans, minute hairs, which are sensitive to touch, are found growing out from the body covering. At the base of these hairs are found neurones which send axons inward to the central nervous system. [Illustration: Nerves in the skin: _a_, nerve fiber; _b_, tactile papillae, containing a tactile corpuscle; _c_, papillae containing blood vessels. (After Benda.)]