THE CONQUEST OF NATURE 



sole function of the muscle is to contract. It can, of 

 course, relax, also, to make ready for another con- 

 traction, but this is the full extent of its activities. A 

 microscopic examination of the muscle shows that it is 

 composed of minute fibres, each of which on contraction 

 swells up into a spindle shape. A mass of such fibres 

 aggregated together constitutes a muscle, and every 

 muscle is attached at either extremity, by means of a 

 tendon, to a bone. Both extremities of a muscle are 

 never attached to the same bone otherwise the muscle 

 would be absolutely useless. Usually there is only a 

 single bone between the two ends of a muscle, but in 

 exceptional cases there may be more. As a rule, the 

 main body of a muscle lies along the bone to which 

 one end of it is attached, the other end of the muscle 

 being attached to the contiguous bone placed not far 

 from the point. The first bone, then, serves as a ful- 

 crum on which the second bone moves as a lever, and, 

 as already pointed out, the familiar laws of the lever 

 operate here as fully as in the inanimate world. But 

 a moment's reflection will make it clear that the object 

 effected by this mechanism is the increase of motion 

 with relative loss of energy. In other words, the muscu- 

 lar force is applied to the short end of the lever, and a 

 far greater expenditure of force is required when the 

 muscle contracts than the power externally manifested 

 would seem to indicate. 



A moment's consideration of the mechanism of the 

 arm, having regard to the biceps muscle which flexes 

 the elbow, will make this clear. If a weight is held 

 in the hand it is perhaps twelve inches from the elbow. 



[44] 



