19$ REFLEX MOVEMENTS. 



messages to all the muscles instead of only to those 

 whose contraction would be useful. 



Nerves merely carry messages to and fro. Nerve- 

 centres do much more than this; they guide the mes- 

 sages to the various organs, and, in all ordinary circum- 

 stances, make them work for the general welfare of the 

 body. Most nerve-centres do this independently of our 

 will; they set the proper muscles at work whether we 

 like it or not, though the cerebrum, which is the largest 

 nerve-centre and only one where the will acts, sends 

 out most of its messages in answer to the will. When 

 food goes the wrong way and gets into your larynx 

 (p. in) you cannot help coughing; when something 

 comes rapidly close up to your eye you cannot help 

 winking; when you chew food you cannot prevent your 

 salivary glands (p. 109) from pouring out extra secretion. 

 All such useful movements, guided by nerve-centres, and 

 not dependent on our will, are known as re flex movements. 

 Sometimes we notice them, though we cannot hinder 

 them, but far oftener we know nothing about them. 

 These unconscious reflex movements, guided by the 

 nerve-centres, carry on nearly all the regular daily work 

 of the body necessary to keep it alive. They regulate 

 the circulation and the breathing, and the secretion of 

 the digestive liquids, and so on. The medulla oblongata 

 especially regulates the beat of the heart and the breath- 

 ing movements; if it is seriously injured, death occurs 

 very quickly. 



If we had to think about and will every beat of the 



what are " convulsions" due? What is the function of nerves? Of 

 nerve-centres ? How do most nerve-centres behave as regards our 

 Will? Illustrate. Explain what is meant by reflex movements. What 

 is said of our consciousness of them ? Of their use ? 



