THE NERVOUS SYSTEM 131 



even to awaken has great presumption. If one does not rise promptly 

 upon waking naturally, the instinct to awake when enough sleep has 

 been taken will be lost, and the habit of sleeping too much will be 

 formed, and the brain, like the muscles, will become weak from 

 inactivity. Infants sleep most of the time, and it is injurious to them to 

 be waked. Adults usually require about eight hours of sleep. There is 

 a risk in going to sleep in a warm room, for the bed covering which is 

 comfortable then may not be enough to prevent taking cold when the 

 fire goes out. Sleep usually comes more promptly to one who goes to 

 bed at the same hour each night. The muscles are relaxed in sleep, 

 and relaxing them perfectly upon lying down and breathing slowly, 

 tends to bring sleep. One who is sleepless usually finds that he is 

 breathing fast and is holding the head stiff on the shoulders, the teeth 

 clenched, and the muscles contracted, even though he is lying down. 

 Excitement and worry during the day, but especially just before retiring, 

 tend to produce sleeplessness. One who overworks his mind by too 

 great attention to business is inviting ruin. A student who loses sleep 

 while preparing for an examination will probably . fail. Rested brain 

 ce.lls and pure blood are needed for good work. 



Rules for Preventing Sleepiness. (i) Do not sit close to stove or 

 especially a fireplace or in very warm room, and do not wear very 

 warm clothing in the house. (2) Let in fresh air freely. (3) Do not 

 sit in rocking chair nor with chest flattened. (4) Make the last meal a 

 very light one. 



Habits. Our habits of doing and thinking and feeling 

 really constitute our characters. This shows the impor- 

 tance of right habits. By gradually changing our habits 

 we can strengthen our characters and form them somewhat 

 as we wish. When a muscle contracts in a certain way, 

 this act makes it easier for the muscle to contract in that 

 way the next time ; thus great muscular strength may be 

 developed. When a nerve cell acts, the circulation around 

 the cell is increased, the fibers develop by use, and the act 

 is easier the next time. We cannot entirely get rid of our 

 habits, because we cannot get rid of our brains. 



Healthy fatigue is caused by the accumulation of waste 

 products resulting from the oxidation of substances in 

 nerve, muscle, and gland cells. The presence of waste in 



