CHAPTER IX 

 THE DIGESTION OF THE FOODSTUFFS 



BY digestion most of the foodstuffs undergo physical and 

 chemical changes by which they are prepared for absorption 

 into the blood. Only a few foodstuffs, e.g. water, salts, 

 grape-sugar, can become part of our body without any 

 change. The most 'important alimentary principles, pro- 

 teids, fats, and many carbohydrates cannot be absorbed in 

 the form in whch they are furnished by nature. 



The digestion proper is preceded by a mechanical tritura- 

 tion of the solid foods by biting and chewing. 



Digestion itself consists of rendering the insoluble or 

 .slightly soluble and non-dialyzable foodstuffs soluble and 

 dialyzable. This is brought about by the digestive ferments 

 which, by hydrolytic splitting up, form smaller molecules 

 from the large molecules of the native foods. In this 

 manner proteids are split up into proteoses ; starch into 

 sugar; fats into glycerin and fatty acid. 



The organ in which the digestion is carried on is the 

 alimentary canal (tractus intestinalis) ; it consists of mouth 

 and esophagus, stomach, small and large intestine. 



1. DIGESTION IN THE MOUTH 



i. Mechanical changes of food in the mouth. The 



mechanical processes in the mouth consist of cutting (biting), 

 chewing, and sucking. 



Biting serves to cut off proper portions of the food. The 

 morsel is ground up more or less by chewing and, being 



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