CHAPTER XV 



CLASSIFICATION OF FOOD. — DIGESTIVE PROCESSES; CHANGES 

 THE FOOD UNDERGOES IN THE MOUTH, STOMACH, SMALL 

 AND LARGE INTESTINE; ABSORPTION 



Digestion. — The process of digestion takes place in the ali- 

 mentary canal, and the purpose of it, as stated in a previous chapter, 

 is to change the food that we eat into a soluble form, so that it can 

 pass through the intestinal membranes and be absorbed by the 

 blood. 



Definition of food. — A food may be defined as a substance that 

 contains one or more of the constituents found in the body, or a 

 substance which the tissues of the body can act upon and convert 

 into material for the production or repair of living tissue, or to 

 yield energy. 



CLASSIFICATION OF FOOD 



As commonly used the term food includes everything that we 

 eat and drink and comprises a great variety of substances. 

 Chemical analysis enables us to divide all these substances into 

 two great classes, and these are further subdivided as follows : — 



1. Inorganic I ^' . . 



[ Alnierai matter or salts. 



I" Proteins. 



2. Organic < Carbohydrates. 



[ Fats. 



Water. — Water (HoO) is a very stable compound of hydrogen 

 and oxygen. It does not yield energy, but it does enter into the 

 composition of all the tissues, supplies fluid for the body, acts as 

 a solvent for food, and aids in the elimination of waste. Next 

 to air it is the most necessary principle of life and constitutes about 

 two-thirds of the body weight (66 per cent). 



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