44 THE ENGINES OF THE HUMAN BODY 



difficulty of balancing the action of our muscles, for all of 

 them have to act as perfectly adjusted reciprocal engines. 

 No wonder it is difficult to become expert at games or at 

 skilled work ! We see, too, what a wonderful machine the 

 human body is. When we take even a single step we 

 set three hundred engines in motion, we set each going at 

 the right instant, and from each of the three hundred 

 messages are streaming into the brain and an equally 

 great number are being dispatched outwards from auto- 

 matic control centres. 



Perhaps I have extolled the merits of muscular engines 

 quite enough already, although I have not exhausted all 

 their merits. They run so silently that they do not seem 

 to make any noise at all, and yet if you apply your ear 

 to -the biceps when it is set in motion, or especially 

 if you listen to it with a physician's stethoscope, you 

 will find that a muscle is not altogether a noiseless engine. 

 Nor do muscular engines throw out ill-smelling gases ! 

 Then they never really stop ; even if they are not 

 actually performing mechanical work their engines are still 

 kept running free, with their clutches off ; but the clutch 

 slips in automatically when we want to set the human 

 machine in motion. Moreover, they are so wonderfully 

 geared that we can change the speed as often as we like 

 and to what degree we choose. Muscular engines always 

 have their " steam up " and are ready to start work at 

 an instant's notice. At the time these lectures were being 

 given the ships of the British Fleet, which were lying in 

 harbour, had to keep their furnaces alight day and night and 

 their steam up, because no one knew the hour or minute 

 they might have to sail. In order that the fleet might be 

 ready on an instant to protect the life of Britain, endless 

 tons of coal and oil had to be burned — wasted. The 

 ideal engine would be one that completely stopped when 

 not wanted, and yet was ready for action in the hundredth 

 fraction of the time taken to twitch an eyelash. Muscular 

 engines must often work quite as quickly as that to save 

 the life of the human body. But even Nature has not 

 invented so perfect an engine. Muscular engines have 



