THE SCIENCE OF HAPPINESS 



not for the further fact that all the various organs of 

 the human body are linked together and in some degree 

 mutually dependent. Thus the muscles, though their 

 direct and primary function is to contract, have a 

 scarcely less important secondary function in their 

 influence over the other organs. This influence is 

 exerted through two patent channels, the blood-vessels 

 and the nerves. 



Every muscular contraction, besides tending to pro- 

 duce a movement of some portion of the body, com- 

 presses the veins in and about the substance of the 

 muscle, and accelerates the flow of blood in these vessels. 

 Muscular contraction is therefore, within reasonable 

 limits, a direct aid to the heart in keeping up the circu- 

 lation of the blood. And since every organ of the body 

 (including, of course, the brain) depends absolutely 

 upon its blood-supply for its power of vital activity, the 

 indirect influence of the muscles, exerted through the 

 blood-vessels over every other organ of the body, is of 

 vast importance. 



The influence exerted through the nerves is not quite 

 so tangible, but even more important. The muscle 

 cell and the brain cell are like poles of a battery, a nerve 

 being the connecting wire. Vital impulses travel back 

 and forth over this nerve, and the integrity of these im- 

 pulses is dependent upon the integrity of the cells at 

 either end, as well as upon the integrity of the nerve it- 

 self. Let the nerve be severed, and both muscle cell 

 and brain cell will in part lose their function, and tend 

 to suffer degeneration. Under ordinary conditions the 



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