THE NERVOUS SYSTEM 



avoidance of worry promotes sound sleep at night. The 

 sleeping room should be cool, but it is not necessary that 

 water freeze in the pitcher. It 

 should be well ventilated, a win- 

 dow being left partly open even 

 in moderately cold weather in the 

 northern states, and in very cold 

 weather in the Gulf states, unless 

 the room is loosely built. 



570. Effect of Activity of Nerv- 

 ous System. If the cells of any 

 tissues are not active, they become 

 weakened. It is the same with 

 the nervous system. Fresh and 

 new sensations are necessary for 

 the health of the brain ; those 

 mental faculties that are used be- 

 come strong. Unused muscles FIG. 210. A study of Fatigue. 



flabby and ill-nourished Portions of nerve cells from the spinal 



ganglia. A, resting cell. , cell 



because the circulation in them 



from a ganglion that had been elec- 

 trically eliminated for five hours. 

 The shrinkage of the nucleus and 

 structure of the fatigued cell is 

 marked. 



is weakened ; the circulation in 

 inactive nervous tissue also be- 

 comes less active. Mental activity 

 strengthens the nervous system and the body in general. 

 If one protects his sensory nerves by too warm clothing 

 and never lets the cold air strike them, they become weak- 

 ened and unreliable and allow the blood vessels to lose 

 tone. They are likely to do strange things with the 

 circulation, causing colds and disease. If, because of 

 pulpy or soft food, the nerves of the alimentary canal are 

 not stimulated mechanically, peristalsis is weakened and 

 the intestine becomes clogged. The loss of tone in the 

 circulation and the sluggish peristalsis, with the troubles 

 that follow, can often be cured by taking a cold bath every 

 morning. The stimulus to the sensory nerves spreads 



