CHAPTER XLII 

 NERVES AND THE REACTIONS OF ORGANISMS 



250. What we cannot help doing. No child can keep his 

 face composed and look unconcerned when he is properly 

 tickled. He bursts out laughing, or he draws away the tickled 

 part, or he does both. And when he does any of these things, 

 he cannot help it. When something suddenly approaches your 

 eyes, you wink, and you cannot help it. 



251. Reflexes. Movements of the kind mentioned, which take 

 place without any intention or desire on the part of the agent, 

 in direct response to some disturbance or stimulation, are called 

 reflexes. Some reflexes are useful, as winking, or sneezing, or 

 coughing, or withdrawing the hand when " it hurts." 



Reflexes need not result in movements. The " funny-bone " reflex 

 carries with it a definite sensation. Indeed, that is about all that we 

 are aware of when the funny bone is struck. This suggests that there 

 are some reflexes that are not altogether confined to movements. We 

 have already come across reflexes that do not involve movements at 

 all. The increased flow of gastric juice in response to the stimulation 

 of pleasant food, and the watering of the mouth on the mere sight of 

 pleasant food, are examples of reflexes that let themselves out in 

 glandular activity. 



252. Using an animal's reflex. If you ever catch a fish with 

 a hook and line, you depend upon a reflex for your success. 

 The fish responds to the vision of certain kinds of objects by 

 snapping at them with his mouth. You simply have to make 

 sure that you have the right kind of bait, and that it is properly 

 fastened to the hook, and that it is dropped into the water at 

 a suitable depth. Your "luck" depends upon the fish seeing 

 the bait, and the reflex does the rest. 



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