CHAPTER XII 



WORKING OVER THE BODY'S INCOME 



Questions. 1. What happens to food after it is eaten? 2. How does 

 the food which we place in the mouth and swallow get to the other 

 organs of the body? 3. What connection is there between the stomach 

 and the other inside organs ? 4. Why are some kinds of food more easily 

 digested than others ? 5. What causes indigestion ? 



107. The human food tube. The mouth is the beginning of 

 a long tube inside of which all the digestion takes place. This 

 tube is called the food tube, or alimentary canal. It consists of 

 several fairly distinct regions. It gets to be ten or eleven yards 

 long and is coiled or twisted in parts (see ;, k, Fig. 74). 



108. Mouth digestion. After the food enters the mouth it is 

 crushed and ground by the teeth. The taste of the food, the 

 movement of the jaws, and the rubbing of the food against the 

 inside of the mouth stimulate the saliva glands, that is, set them 

 in action (see Fig. 75). As a result a quantity of saliva is 

 poured into the mouth and becomes mixed with the food. The 

 action of the saliva upon the starch changes it into sugar (see 

 section 105). The other materials in the food are probably not 

 changed, except that salts and sugars are dissolved in water, of 

 which the saliva contains over 99 per cent. 



As the amount of ferment is very small, the effectiveness of 

 saliva in digesting starch depends upon (i) the ferment's reach- 

 ing every particle of starch, and (2) its having sufficient time to 

 act. Mixing saliva thoroughly with the food makes it easier for 

 the mass to slide along into the throat, and down the gullet, since 

 the mass is thus coated with the slippery mucin of the saliva. 



109. Swallowing. After the mouthful of food has been thor- 

 oughly chewed, it is pushed back by the tongue and passed into 

 the throat chamber, or pharynx (see b, Fig. 74), from which it 



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