46 .THE ENGINES OF THE HUMAN BODY 



some hours, the available store of fuel is used up, and 

 then if pushed to do more it has to fall back on the fuel 

 of its own substance — to use its decks for fuel, as it were. 

 Hence rest is absolutely necessary for muscular engines 

 to give them leisure to restore the supply of material 

 which they change into work — in other words, to fill 

 their bunkers. 



• I have tried to make clear the marvels of the machine 

 which every one of us has to drive. It is a machine 

 which works so easily and so well, especially when we are 

 young, that we think it needs no care or study, and that 

 not even rough usage will damage it. Every night sweet 

 sleep comes when those wonderful muscular engines 

 of ours mend themselves and prepare for the morrow. 

 There is no need for us to spend laborious hours over- 

 hauling them, seeing to their bearings, nuts, and fittings. 

 They do their own repairs. And yet no one can make a 

 greater mistake in life than to suppose that these engines 

 may be neglected with impunity. There is one law which 

 cannot be broken without our being sentenced or punished. 

 That is the law of exercise ; the law that disuse and abuse 

 will ruin any and every muscular engine beyond repair. 

 If a muscle is neglected, if it is not used regularly, it first 

 becomes weak, then it begins to waste, and ultimately it 

 will become useless. Every one of them should be 

 exercised moderately and daily. In the great game of 

 life much of our happiness and our success depends on 

 the treatment we meet out to our muscular engines. 



