220 MENTAL AND PHYSICAL EXERCISE* 



The action of the muscles depend upon the Brain. 

 We have said that the muscles have the power of con- 

 traction, and relaxation, at the will of the animal. We 

 can by no means trace the connection between the ac- 

 tion of the brain in willing, and the action of the muscle 

 in contracting. We know that if all nervous communi- 

 cation between the brain and the muscle be cut off, there 

 will no effect be produced by the action of the brain ; 

 that is, we may will to raise the arm, but the muscles re- 

 main inactive, without the intervention of the nerves. 

 This proves that the nerves, in some way, transmit to 

 the muscles the mandate of the brain ; but how this is 

 done, is a mystery which has never been solved, and 

 most probably will always remain beyond the limits of 

 human knowledge. 



Muscular contraction. When a muscle contracts, the 

 swell becomes enlarged or thickened, and the two ends 

 approach each other. By grasping the thick part of the 

 arm, above the elbow, and bringing the hand towards 

 the mouth, the bulk of the part grasped, will be felt to 

 enlarge, and grow hard, as though it actually contained 

 more matter than before the contraction. 



In this act, the absolute bulk of the muscle is however 

 supposed not to change, though its shape is considerably 

 modified, a part of the bulk towards the extremities, 

 being thrown into the centre ; hence the increased hard- 

 ness, and swelling of this part. The contraction of the 

 muscle appears to consist in the shortening of all the fibres 

 individually, by which, the whole bundle is diminished 

 in length. On the contrary, relaxation appears to be 

 simply the want of contraction, or a passive state in 

 which the muscle ceases to act. 



During sleep all the muscles are in a relaxed and pas- 

 sive state, but when awake we can take no position, 

 except the recumbent one, in which, more or less of the 

 organs are not in an active state. In the standing pos- 



Can we trace any connection between the action of the brain in swel- 

 ling, and the action of the muscle in contracting ? When a muscle con- 

 tracts, how is its shape altered 7 In what does the contraction of a 

 muscle consist 1 In what does relaxation consist ? 



