28 THE MUSCLES. 



their shape, that their extremities are brought nearer to- 

 gether. The bending of the arm, or of a finger, is effected 

 in this manner, by the will; but the will is not the only 

 means of producing this effect. Electricity, a sharp blow 

 over a muscle, and other stimuli, also cause it. Contrac- 

 tion does not always cease with life. In man , : .after death 

 from cholera, automatic movements of hands and feet 

 have been observed, lasting not less than an hour. In 

 certain cold-blooded animals, as the turtle, contraction 

 has been known to take place for several days after the 

 head has been cut off. 



7. The property which, in muscle, enables these move- 

 ments to take place is called contractility. If we grasp a 

 muscle while in exercise (for example, the large muscle in 

 the front of the arm), we notice the alternate swelling and 

 decrease of the muscle, as we move the forearm to and fro. 

 It was at one time supposed that the muscle actually in- 

 creased in volume during contraction. This, however, is 

 not the case ; for the muscle, while gaining in thickness, 

 loses in length in the same proportion; and thus, the 

 volume remains the same in action and at rest. 



8. Contraction is not the permanent, or normal, state 

 of a muscle. It cannot long remain contracted, but after 

 a shorter or longer time, it wearies and is obliged to relax. 

 After a short rest, it can then again contract. It is for 

 this reason that the heart can beat all through life, night 

 and day, by having, as we shall hereafter see, a brief inter- 

 val of rest between successive pulsations. For the same 

 reason, it is more fatiguing to stand for any great length of 

 time in one position, than to be walking the same period. 



9. Relative Strength of Animals. The amount 

 of muscular power which different animals can exert, has 



7. Contractility? Give the illustration. What was supposed? What is the 

 case? 



8. What further in relation to contraction ? Weariness of a muscle ? Beating 

 of the heart ? Standing and walking ? 



9. Muscular power of animals ? How tested ? Man's power ? Worse's ? The 

 comparison ? 



