THE NERVOUS SYSTEM 319 



30. Why do you throw cold water upon a fainting person? 



31. Nightmares are caused by poor circulation of the blood about 

 the solar plexus, which is just behind the stomach. Explain how sleep- 

 ing on the back may bring them on. How eating a heavy supper may 

 cause them. 



32. What is the effect of a thin skin and of a thick skin upon the 

 disposition of a person ? 



33. Why may cold feet cause sleeplessness? 



34. Why does constant moderate drinking undermine the health 

 more than occasional intoxication? 



35. The vasomotor nerves control the size of the blood vessels. 

 Which nerve centers control these nerves ? Why does a draught blow- 

 ing on the back of the neck often cause a cold (Fig. 200) ? 



