FEELING.] PHYSIOLOGY. 131 



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you were to cut across the nervos which lead from the 

 skin of your finger along your arm up to your brain. 

 What would happen? If you pricked or touched 

 your finger, you would not feel either prick or touch. 

 You would say you had lost all sensation in your 

 finger. These nerves ending in the finger then, have 

 a different use from those ending in the muscle. 

 The latter carry impulses from the brain to 

 the muscle, and so, being instruments for 

 J , \, causing movements, are called motor nerves. 

 The former, carrying impulses from the skin 

 to the brain, and being instruments for 

 bringing about sensations, are called sensory 

 nerves. All parts of the skin are provided with 

 these sensory nerves, but not to the same extent. 

 The parts where they abound, as the fingers, are 

 said to be very sensitive ; the parts where they are 

 scanty, as the back of the trunk, are said to be less 

 sensitive. Other parts besides the skin have also 

 sensory nerves. 



Motor nerves are of one kind only ; they all have 

 one kind of work to do — to make a muscle contract. 

 But there are several kinds of sensory nerves, each 

 kind having a special work to do. The several works 

 which these different kinds of sensory nerves have to 

 do are called the senses. 



The work of the nerves of the skin, all over the 

 body, is called the sense of touch. By touch you 

 can learn whether a body is rough or smooth, wet or 

 dry, hot or cold, and so on. 



You cannot, however, by touch distinguish between 

 salt and sugar. Yet directly you place either salt or 

 sugar on your tongue you can recognize it, because 





