316 THE NERVOUS SYSTEM 



use of alcohol, for instance, or fail of their due action 

 upon the food because the preceding processes are incom- 

 plete, the nutriment poured into the blood stream may 

 carry disease instead of health and vigor to brain and 

 nerve. It is just such inconsiderate habits in respect to 

 eating which, as physicians well know, have led to many 

 a serious case of " nervous prostration " among business 

 men or students. 



461. But the blood cannot be kept pure without a con- 

 stant supply of pure air hi the lungs. If that is lacking, 

 there is at once defective nutrition of the nerve cells. 

 Undoubtedly the nervousness so common among women 

 is due, more than to any other one cause, to an insufficient 

 supply of pure air for the lungs. Tight clothing which 

 restricts the capacity of the chest, lack of outdoor exer- 

 cise, and the breathing of vitiated and usually (in winter) 

 too warm air are all direct causes of nerve weakness. 



462. One more condition is necessary in order that the 

 blood may be pure, and that is a healthy activity of the ex- 

 cretory mechanisms. If the worn-out material from .the 

 wasting tissues is not removed, it will remain to clog and 

 poison the vital current. In a word, the condition of the 

 brain and spinal cord, and the vigor and readiness of nerv- 

 ous reaction, depend wholly upon the distribution and 

 quality of the blood, and those depend upon food, diges- 

 tion, respiration, and excretion. It is true that a man 

 does not die at once or become diseased because he has 

 eaten improper food or breathed foul air. The physical 

 organism has marvelous powers for contending against 

 unfavorable conditions, a wonderful way of throwing off 

 poison and rebounding from depression, so long as the 

 natural vigor of tissues is not impaired by persistent 

 abuse. But for each individual there is a point beyond 



