CHAPTER XVI 



A SURVEY OF THE WORKSHOPS AND LABORATORIES OF THE 

 HUMAN BODY, WHERE FOOD IS TURNED INTO FUEL 

 FOR THE TISSUES 



In order that a machine may perform work, be it made of 

 metal or of living flesh, it must be provided with a system 

 of parts which will maintain a constant supply of the food, 

 aliment, or fuel consumed in the combustion chambers 

 of the machine. To an arrangement of parts of this kind 

 human physiologists give the name of alimentary system. 

 In the human machine we shall find that this system is 

 made up of a series of workshops or laboratories linked 

 together by a novel and cleverly contrived transport 

 system, while in the motor cycle the parts are few and 

 arranged in the simplest plan conceivable. 



Before proceeding to compare the alimentary system of 

 a motor cycle with that of the human body, it may be 

 well to answer an objection which is likely to be raised by 

 the reader at this point. He may question whether the 

 word fuel — a substance which can be burned in an engine 

 — may be applied rightly to the food or aliment which is 

 consumed by human beings. The answer of the modern 

 physiologist on this point is decisive. He has found that 

 a pound of sugar, whether consumed in the combustion 

 chamber of an engine or in the myriad recesses of the 

 human body, gives off in each case exactly the same 

 amount of heat. He estimates the value of a food just 

 as an engineer estimates the value of a fuel by measuring 

 the amount of heat it gives off when burned. A human 

 machine of medium size and doing strenuous manual 



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