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brgans of digestion and circulation, etc., must be kept in good 

 order for its preparation and distribution. In short, whatever 

 tends to produce a healthy body also tends, indirectly, to main- 

 tain a good condition in the nervous system. Exercise, therefore, 

 is as valuable to the brain worker as it is to the laborer, and per- 

 haps even more so, in that the latter is apt to neglect muscular 

 activity, while the very work of the laborer tends, to keep his 

 system in order. 



Air supply. — The chemical changes which take place in the 

 nerve cells are essentially similar to those in the muscle cells, in 

 that the production of energy or action involves the oxidation of 

 cell substance and food. It follows, therefore that not only must 

 the nerve cells receive food but also a plentiful supply of oxygen. 

 The brain responds very quickly to a lack of air by a feeling of 

 dullness and headache, and it is extremely important that our 

 school and living rooms be well ventilated. Exercise that tends 

 to develop the lung power is likewise valuable. 



Rest. — Like the muscle cells, again, the nerve cells accumu- 

 late wastes and consume food by continued activity. It is imper- 

 ative, therefore, that they be allowed periods of rest when the 

 supply of food may be renewed and the excess of waste removed. 

 Sometimes, as with the muscles, a change of work will permit one 

 set of Cells to rest while another is working, and thus a change 

 of occupation is a rest. But no person can work continuously 

 and maintain a healthy nervous system, and for that reason sleep 

 is nature's greatest remedy for tired nerves. Children whose 

 nerve cells are growing should have plenty of sleep in order that 

 their nerve cells may store up sufficient food in these rest periods 

 to meet the daily needs, and at the same time permit of growth 

 and branching. On this account adults whose cells have attained 

 their normal size need less sleep than children. 



Nerve cells are like muscle cells in another particular, in that 

 they degenerate by disuse and lose their irritability. The person 

 who is too careful of overtasking his nervous system may carry 

 this care to excess and lose his mental power entirely. It is this 

 need of constant nerve exercise which gives especial value to a 

 general education, since the variety of subjects in such a coiirse 

 insures the normal development of all parts of the system. 



