6 THE ENGINES OF THE HUMAN BODY 



thought that the only people who should become rich 

 were the families and the men who gave their lives for 

 our country, but we could not find out a plan that would 

 bring that about. But I hope the boys and girls for whom 

 I am now writing — if war should ever come again — will 

 find out a way and put it into practice when they grow up 

 to be men and women. Well, at that Christmas time one 

 of those men who had become very rich had an only son 

 whom he spoiled by giving him everything that he asked 

 for, and as a Christmas gift gave him a new motor cycle 

 of the latest pattern. Now you will scarcely believe me 

 when I tell you that this boy, whom you think so fortunate, 

 was very discontented. He wanted to mount the machine 

 at once and go careering along the streets and roads but 

 could not because he did not know anything about 

 how engines are made, how they work, how they are 

 started or how they are stopped. If I ask you, What 

 is a boy in a case like this to do ? — 1 think I can guess 

 your answer. You will say that he must seek help from 

 books, consult men who are expert drivers, learn the use 

 of each part — how petrol and air are drawn into the 

 combustion chamber of the engine to form an explosive 

 mixture, how that mixture is fired, and how the force thus 

 set free is made to turn the back wheel with a power that 

 will carry the rider up the steepest hill. You will say 

 that this boy is unreasonable in expecting to be able to 

 work so complex a machine all at once seeing that it has 

 taken thousands of clever men, working through many 

 centuries, to invent and perfect the one which has now 

 come into his possession. I have no doubt that such will 

 be the answer you will make, and I for one shall agree with 

 you. Now it so happens that you and I have been pre- 

 sented with a machine — you only a few years ago, I a great 

 while since — the human machine ; one which you and 1 

 have to mount and drive every day of our lives. It is 

 full of the most cunningly contrived inventions ever seen 

 or dreamt of, inventions which have taken millions of 

 years to work out and perfect. Clearly, then, if it is 

 necessary to understand a machine which we mount only 



