402 THE NERVES AND THE SENSE ORGANS 



operation. But if the sensation in the stomach is not a 

 normal one, but one of injury, the message goes to the 

 cerebrum, and we feel pain. 



The action of the sympathetic system upon the blood vessels of the 

 skin is well illustrated by the phenomenon of blushing. When we 

 have some unusual emotion (it may come from an insult or a com- 

 pliment), the sympathetic nerves cease, for a time, to control the blood 

 vessels that come to the skin. As a result, the blood rushes into them, 

 until the skin is red and hot. Then the sympathetic system gets back 

 its control over the blood vessels, causes them to contract, and turns 

 the excess of blood away from the skin. There is a very close con- 

 nection between our emotions and the way in which our internal 

 organs carry out their work. Thus, unpleasant emotions, such as 

 anger, fear, and worry, seriously affect the digestive system. They 

 cause a partial paralysis of the nerve structures that control the 

 digestive organs, and make good digestion impossible. 



403. The Nervous System as a Whole. If we could 

 remove all the remainder of the body : muscles, bones, and 

 organs, leaving only the nerve structures, we should have 

 a " nerve skeleton," which would preserve the general 

 outline of the body. This is another way of saying that 

 "nerves" go to all parts of the body. How are the 

 "nerve connections" made that put an organ (the foot, 

 for example) into communication with the brain? We 

 might guess at the answer, and say that the nerve fibers 

 (axons) are fastened together, much as pieces of rope are 

 spliced, or as wires are soldered together. But this does 

 not seem to be true. So far as we know, there is no 

 actual joining (or at most only a slight joining) of the 

 neurons. The axon has, at the end farthest from the 

 cell body, a number of short branches, called the end 



