INFLUENCE OF EXERCISE ON THE BRAIW 



food. On the contrary, it is often the result, among 

 the higher classes, of too much or too stimulating 

 food over-exciting and ultimately impairing the di- 

 gestive powers. The proneness to morbid excite- 

 ment in the brain, induced by insufficient food, is 

 one cause why, in times of public distress, the 

 lower orders are so apt to resort to violence to re- 

 move the sources of their discontent. 



The THIRD condition of health in the brain and 

 nervous system, and that to which it is the chief 

 object of these pages to direct attention, is the 

 regular exercise of their respective functions, ac- 

 cording to the laws already so frequently referred 

 to, and so fully explained in one of the preceding 

 chapters.* 



The brain, being an organized part, is subject, in so 

 far as regards its exercise, to precisely the same laws 

 as the other organs of the body. If it be doomed to 

 inactivity, its functions languish, and its health de- 

 cays. If it be duly exercised, after regular inter- 

 vals of repose, its functions acquire readiness and 

 strength ; and, lastly, if it be over-tasked, either in 

 the force or duration of its activity, its functions 

 become impaired, and irritability and disease take the 

 place of health and vigour. 



The consequences of inadequate exercise may be 

 first explained. 



We have seen that, by disuse, muscle becomes 

 emaciated, bone softens, blood-vessels are obliter- 

 ated, and nerves lose their characteristic structure. 

 The brain is no exception to this general rule. Of 

 it also the tone is impaired by permanent inactivity, 

 and it becomes less fit to manifest the mental powers 

 with readiness and energy. Nor will this surprise 

 any reflecting person, who considers that the brain, 

 as a part of the same animal system, is nourished 

 by the same blood, and regulated by the same vital 

 laws, as the muscles, bones, and nerves. 



* See Chapter IV., and also p. Ifr. 



