CHAPTER XVIII 



THE SPECIAL SENSES AND SENSATIONS 



171. Sensations. We have learned that the general 

 plan of the nervous system is to have nerves run to the 

 brain and spinal cord, which convey impressions from 

 all parts of the body to the central organs, and then 

 another class of nerves to convey messages issued by 

 the central organs to the muscles and glands in all 

 parts of the body. The first are sensory nerves and the 

 second motor nerves. In this chapter we shall study 

 the organs from which the sensory nerves start, and 

 learn what the brain does with the impressions which it 

 receives. 



The brain receives impressions, and, in some way 

 not understood by scientists, gives them meaning. We 

 say the mind has the power to interpret these impres- 

 sions or transform them into sensations. Every sen- 

 sory nerve, whether from the eye or stomach, the ear 

 or lungs, the tongue or toes, brings impressions from 

 which we gain a knowledge of our own bodies and of 

 the world about us. The moment an object comes in 

 contact with the hand, certain little organs in the skin 

 receive the impressions, and nerves carry these impres- 

 sions to the sensory areas of the brain, and we become 



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