384 THE HUMAN MACHINE 



Although the human body is like an engine, it differs from it 



in the way it uses its (1) All work is done in the (2) of 



the body. Food is (3) to release energy. Food must be 



made (4) or digested so that it can get into the cells. Digestion 



takes place in the food tube and is brought about by the action of 



substances called (5) Starches, fats, and proteins are each 



(6) by different (7) After the foods are digested, they are 



(8) into the blood, taken to the cells, and then (9) there. 



Oxygen from the air is taken into the (10) and from there 



carried by the (11) to the cells, where it (12) with the 



food substances and releases (13) The (14) products 



are carried away by the blood. 



STORY TEST 



PHILIP TELLS ABOUT AN EXPERIMENT 

 Read carefully and critically. List all the errors and suggest corrections. 



We saw an experiment the other day that showed why we should 

 chew food. The teacher took two pieces of hard-boiled egg exactly 

 the same size. Then he chopped one piece up fine and left the 

 other as it was and then put the two lots of egg into two test tubes. 

 Each tube was about half full of some stuff he called artificial 

 digestive juice. I think this juice contained an acid, for, after he 

 left the tubes for half an hour in warm water, we looked again 

 and found that the big piece of egg was not changed but the little 

 pieces were all gone and the substance in one tube looked milky. 

 I guessed that the acid dissolved the small pieces of egg. I don't 

 see why it didn't break down the big piece of egg, unless it was 

 because it wasn't strong enough. 



PROBLEM V. HOW DO WE CONTROL 

 THE HUMAN MACHINE? 



How the Nervous System Works. You have all seen 

 a race of sprinters. At the start all is attention. The 

 runners get set. Every muscle is tense awaiting the 

 starter's gun. Then off they go. What has happened? 

 The boys in the race have been alert to listen for the sound 

 of the starter's gun. Then the messages travel from the 

 ear to the brain, and from there messages go to the muscles 



