CHAPTER VI 

 A STUDY OF BLOOD MANUFACTURE 



Definition of Digestion. In the preceding chapter we dis- 

 cussed the composition of foods, the methods of cooking, 

 and the uses of foods to the body. We shall now follow 

 the changes that take place in these foods, for before the 

 different nutrients can be supplied to the brain, the muscles, 

 or the bones, they must be changed from a solid or semi-fluid 

 condition into liquids that can be absorbed. This process is 

 called digestion. It is carried on within our bodies in a 

 complicated tube nearly thirty feet in length, which is 

 called the al-i-men'ta-ry canal (Latin alimentum = nourish- 

 ment). Digestion, then, may be defined as the series of changes 

 within the alimentary canal by which food is made ready to 

 become a part of the blood. 



Parts of the Alimentary Canal. The alimentary canal be- 

 gins at the mouth opening, enlarges to form the mouth cavity, 

 and this in turn communicates behind with a somewhat smaller 

 throat cavity. Posterior to the throat is the e-soph'a-gus or 

 gullet, which conducts the food into an enlarged pouch, 

 the stom'ach. Most of the lower half of the trunk is filled 

 with the much coiled in-tes' tine, which begins at the stomach 

 and opens to the outside of the body at the posterior end of 

 the trunk. 



Digestive Glands. Several important organs, called diges- 

 tive glands, lie adjacent to the alimentary canal, but con- 

 nected with it. They produce digestive juices, which flow 

 into the food canal through small pipes or ducts. The sal'- 

 i-va-ry glands pour their secretions into the mouth cavity. 



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