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APPLIED PHYSIOLOGY 



tooth is decaying and needs filling. If we could not feel 

 pain, an arm or a leg might be burned or cut without our 

 knowing it. 



283. Temperature. We feel heat or cold by special 

 nerves in the skin. Draw a cold pencil point slowly over 

 the face. You feel its touch as it moves over your face, 

 but at a few points you feel only a coldness. These points 

 are scattered over the skin so close together that the whole 

 skin seems to feel the sensation. Whenever heat or cold 

 is great enough to harm the body, we feel only a pain. 



a bone of the orbit. 

 b muscle which moves 



the eyeball. 

 c sclerotic coat. 

 d choroid coat. 



The human eye. 



e retina. 

 / eyelid. 

 g ins. 

 h lens. 



t cornea. 



j muscle which changes 



the shape of the 



lens. 

 k optic nerve. 



284. The eye. The eye is a round white globe filled 

 with a clear fluid. In its front is a clear round window, 

 behind which is a muscular curtain called the iris. The 

 iris is blue or brown, and gives the color to the eye. In its 

 center is a round black hole called the pupil. The pupil 



