CHAPTER IX 



PHYSIOLOGY OF THE DIGESTIVE ORGANS. 

 FOODS, DIGESTION, ABSORPTION 



FOODS 



The human body is a machine constantly in motion; therefore, 

 its cells continually use up their force, and continually need renew- 

 ing. The material for this renewal is supplied by the food which 

 we eat. Substances classed as foods must be able to "repair waste 

 and provide the raw materials for growth. All substances which 

 have this power are foods. . . . Thus, water salts and oxygen 

 are true foods" (Mathews). As the various parts of the body 

 are composed of quite different tissues, so the food is of a mixed 

 character. 



The composition of the tissues includes four classes of food 

 principles, as follows: 



1. Proteins. 1 



2. Carbohydrates (sugars and starches). \ organic. 



3. Fats. 



4. Mineral salts including water. inorganic. 

 In the body : 



1. Proteins are found in all tissues, but most abundantly in 

 blood, as serum-albumin, fibrinogen, hemoglobin; lymph, as serum- 

 albumin; muscles, as myosinogin; milk, as caseinogen. 



2. Carbohydrates (sugars and starches) are found principally 

 in blood, as dextrose; liver and muscles, as glycogen; 1 milk as 

 lactose. 



3. Fats are found principally in milk, as an emulsion; nerves, 

 lymph, blood cells; bones, a? marrow; subcutaneous fascia and 

 adipose tissue around organs. 



4. Mineral salts are found in all tissues and fluids of the body; 



1 Glycogen is an animal starch formed within the body, the others are sugars. 

 Dextrose, grape sugar and glucose have the same composition. 



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