CHAPTER II. 

 MOTION. 



Motion and Life. Motion is the most manifest sign of 

 life. While we are sitting still, as we say, there are fre- 

 quent slight motions of the head, body, and limbs. Even 

 during sleep the movements of breathing may be seen ; 

 the hand laid upon the chest may feel .the beating of the 

 heart, and the finger detect the pulse in a number of 

 places. 



We must move to get our food, or at least to eat and 

 digest it. Motion is necessary for breathing, for circu- 

 lating the blood, for getting rid of wastes. We often move 

 to avoid injury. 



Motion is necessary for seeing : we must turn the face 

 toward the object; we move the eyeballs; within the eye 

 are motions to regulate the amount of light admitted, and 

 to adapt the eye for seeing at different distances. 



In feeling, we put forth the hand to touch the object. 

 In tasting, we touch the tongue to the object. In smelling, 

 we sniff ; and sniffing is a respiratory motion. In hearing 

 and in speech there is also motion. 



How are all these motions produced ? 



Experiments with the Muscles in our own Bodies. i. Clasp 

 the front of the right upper arm ; draw up the forearm strongly 

 and as far as possible. Note what changes are felt in the biceps 

 muscle. 



2. Repeat the experiment, and with the thumb and finger feel the 

 cord, or tendon, at the lower end of the muscle, just within the angle of 

 the elbow. 



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