REFLEX MOVEMENTS. 197 



which carry towards a centre are usually called sensory 

 fibres, because when they work they very often cause 

 some sensation or feeling. The fibres which carry from 

 a centre are named motor fibres, because they usually 

 cause some muscle to contract, and thus produce move- 

 ment. The first set of nerves is also sometimes called 

 afferent (from a Latin word meaning bringing to), and 

 the other set efferent (from a Latin word meaning to 

 bring from). These names are better than sensory and 

 motor, because many nerves carry messages to centres 

 without our having any sensation of them, and many 

 nerves carry messages from centres to other organs than 

 muscles, for example to glands. 



9. Reflex Movements. As we have seen, a great deal 

 of the orderly working of our organs is brought about 

 without our will, or even without our knowing about it. 

 When a message comes to a nerve-centre, the centre does 

 not merely send out random messages along any outgo- 

 ing nerve-fibres, but, as it were, first selects the organs 

 to be set at work, and then sends the proper messages. 

 As, for instance, in the case of sneezing. If the centre, 

 warned by the sensory nerves of the nose, should set at 

 work any or every outgoing fibre joined to it, the result 

 would not be a sneeze, but some sort of a shaking-up or 

 convulsion of the whole body. It might once in a thou- 

 sand times be useful, but in most cases would do more 

 harm than good. The disease known as " convulsions" 

 is due to the fact that the nerve-centres, whenever a 

 nerve-fibre brings a message to them, send out random 



9. How is the involuntary working of our organs managed by the 

 nerve-centres ? Illustrate from the case of sneezing. What happens 

 if the nerve centres send out messages to the wrong organs? To 



