CHAPTER XII 

 THE HYGIENE OF THE NERVOUS SYSTEM 



In previous chapters we have given some accbunt 

 of the nervous system and the sense-organs. We 

 have seen that, from an objective point of view, the 

 purpose of the nervous system is to transmit impulses 

 derived from external stimuli and to apply them through 

 the effectors (muscles and glands) to secure useful 

 adaptive reactions. The health or normality of a sys- 

 tem with such a duty is clearly all-important. In 

 this chapter we shall treat of its conservation in the 

 briefest fashion. 



Habit. It is a property of the brain to be modified 

 by use. We say that paths of easy transmission are 

 formed in it when certain acts have been repeatedly 

 performed. This is the basis of skill and economy of 

 power. It is nearly related to the formation of habits. 

 A habit may be considered an acquired, personal re- 

 flex, as we have already suggested. Things which are 

 habitual we speak of as " second nature" and if we stop 

 to consider what this means we shall find the idea to be 

 that certain circumstances lead regularly to certain 

 performances. 



The capacity to form habits is of the greatest value. 

 As we master one accomplishment after another we 

 are set free from irksome attention to details and can 

 attempt something new. A child that is putting on its 

 clothes may not be able to think of anything but the 

 task at hand; the same is true of the youth who first 

 applies the razor. Thanks to the emancipating virtue 

 of habit-formation, the grown man dresses and shaves 

 while his mind is busy with more interesting matters. 



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