INTERNAL-COMBUSTION ENGINES 31 



Many millions of years before man had thought about 

 motor cycles, Nature had invented a method of making 

 each stroke of the muscular engine effective. She did 

 this by means of a wonderfully contrived pump called 

 the heart. It is this pump which maintains a constant 

 circulation through the muscular engine we are now 

 considering — the biceps. Through the arteries it pumps 

 into the muscle blood which contains both fuel and air — 

 an "explosive mixture"; the blood returns by the veins 

 laden with waste products. The biceps does not look at 

 all like the engine of a motor cycle, but when we look 

 beneath the surface we see that they have corresponding 

 parts. 



We now come to a question which is very difficult to 

 answer clearly. Does the biceps of your arm, when it 

 contracts and bends the elbow, really act as an internal- 

 combustion engine ? Long ago Faraday delighted boys 

 and girls in the Royal Institution at Christmas time by 

 showing them that all the secrets of combustion can be 

 studied in a lighted candle — the hydrogen and carbon 

 elements which, locked up in the tallow or wax of a candle, 

 begin to unite with the oxygen of the air when a lighted 

 match is applied to its wick. As every boy knows, water 

 and carbon dioxide are formed in the process of burning 

 or combustion, and heat is also given off or generated. 

 The same thing occurs in the combustion chamber of an 

 engine when an electric spark fires the mixture of petrol 

 and air. The hydrogen and carbon elements of the 

 petrol instantly unite with the oxygen of the air, causing 

 an explosion. The explosion spends its force in thrusting 

 down the piston and thus driving the engine ; heat is 

 generated, water and carbon dioxide are produced — all 

 being the results of "internal" combustion. Now, if 

 we can show, when a muscular engine is set in motion, 

 that carbon dioxide and water are formed and that heat 

 is given off, then we should have grounds for think- 

 ing that there is another point of likeness between a 

 motor cycle and a human body — both are fitted out with 

 internal-combustion engines. 



