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THE HUMAN MACHINE 



the words you read, and in the cells of the brain which 

 you use in thinking about what you read. Hundreds, 

 perhaps thousands, of cells are involved in the simplest 

 processes of daily life. So you see it is far from simple 



How does food get to the cells ? What happens to food in the cells ? 



to explain just how the human machine makes use of the 

 food it takes in. Not only must the food be put into a 

 condition so that it can get out of the digestive tract into 

 the cells, but it must also be carried to these cells. In 

 addition, if the food is to be oxidized, oxygen is used. 

 This must get in from the air and be passed to the cells. 

 Three systems of organs accomplish this work. First, 

 the digestive tract prepares the food, or digests it, so that 



oxyg&n. 



a capillary 

 Cccrries " 

 useful 

 materials 

 to needy cells 



it contracts 

 and as 

 it Vorks 



it to *ork 



wastes 



a capillary 

 carries ' 

 Wastes from 

 Cells at 

 Vork- 



How does a muscle work ? 



