VII. DIGESTION. 



The purpose of food as shown in the preceding chapter, 

 is to furnish the cells of the body with material out of which 

 they may either make new cells or develop energy. It is 

 evident that a piece of beef, while it may contain all the 

 nutrients necessary to these two processes, is not in the 

 condition to be taken up by the tiny cells of the body and 

 used hj them for these purposes. The beef also contains 

 matter which is of value neither as tissue building material 

 nor as fuel. 



In general, then, all foods require special preparation in 

 order to fit them for use by the cells of the body, and the 

 steps included in such preparation are called digestive 

 processes or collectively, digestion. The processes of diges- 

 tion are of three kinds: First, the separation of a food 

 stuff into its nutrient and non-nutrient parts. Second, 

 the transformation of the nutrients into a liquid form 

 which the cell can absorb. Third, the elimination of the 

 non-nutrient matter. These three processes are prelimi- 

 nary to the use of food by any living cell, and while the 

 means employed must vary with the food, digestion is com- 

 mon to all living forms as the first step in the manufacture 

 of food into living matter and activity. 



In man the processes of digestion take place in a part of 

 the body known as the alimentary canal. 



The alimentary canal. — This canal is a continuous tube 

 extending through the body and having two openings, the 

 mouth at one end and the anus at the other. In some of 



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