THE NERVOUS SYSTEM 313 



a process called assimilation. But suppose one does not 

 work, but is idle, or suppose one works with only a small 

 part of his bodily organs and forces the other organs to 

 loaf; the oxidation in the cells does not take place com- 

 pletely. Instead of urea, uric acid and other poisonous 

 products of incomplete oxidation result. These poisons 

 circulated by the blood to the nerves can give them a tired 

 feeling as effectually as hard work. Often with inactive, 

 idle persons the digestion also becomes sluggish, fermenta- 

 tion takes place and the food is changed to poisons. These 

 additional poisons are absorbed by the blood and carried to 

 the nerves to increase further the tired feeling. Some per- 

 sons never work, yet are always tired and are said to have 

 been "born tired." They belong to this second class. If 

 they did some honest^ vigorous work for a few days, it would 

 lead them to breathe deeply and freely and burn up this 

 refuse material. They would again have that self-confident, 

 buoyant feeling that all men may have and that every man 

 that takes care of his body does have. 



573. The Source of Pain not always where it seems to be. 

 When the " funny bone" is hit, the tingling is referred 

 to the finger, although, of course, the pain is in neither 

 the funny bone nor the finger, but in the brain. If the 

 scar grows too tight over the stump of an amputated arm, 

 the itching that seems to be in the fingers may not stop 

 until the scar is opened by a new cut, and the tightness, 

 which is the source of the pain, is removed. Some forms 

 of neuralgic pains and headaches appear to travel quickly 

 from one part of the face to another. This is because the 

 source of the trouble is not in the face at all, but in the 

 medulla. Bad headaches are not so often neuralgic as 

 from other causes (Fig. 211). When the spine is habitually 

 held crooked, or, in rare cases, some of the vertebrae are 

 displaced by a fall or jar, the circulation may be interfered 

 with near the roots of the spinal nerves, and give the feel.- 



