CHAPTER III 

 HOW FOOD IS DIGESTED 



Making Ready for Digestion. Digestion is more 

 than chewing" and swallowing. Both of these are 

 important, but they are only the beginning of a 

 complicated act that has to do with every con- 

 stituent taken into the mouth as food, regardless 

 of its nature, whether of vegetable or animal origin. 

 Before the several ingredients composing the plant 

 can be used as food they must be prepared for ab- 

 sorption into the system of the animal. This prep- 

 aration takes place in the mouth, the oesophagus 

 tube, the stomach and the intestines. Throughout 

 the process various secretions are supplied to mak& 

 assimilation and absorption into the system pos- 

 sible. 



What Is Done in the Mouth. When food is 

 taken into the mouth, it is masticated by the teeth. 

 While this is going on there are poured into the 

 mouth large quantities of saliva, which soften and 

 soak the foods and start digestion. The active 

 principle of saliva is a soluble ferment called ptyalin 

 that converts the starch into sugar. One authority 

 states that the saliva of a horse will convert raw 

 starch into sugar in 15 minutes. The organic mat- 

 ter contained in this secretion is formed by the cells 

 comprising the structure of the salivary glands. 



A large amount of saliva is soaked up by the food. 

 This is often expressed as being as much as one- 



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