CHAPTER XV 

 HOW FOOD IS PREPARED FOR BODY USES 



Problems : To learn about digestion by studying — 



(a) The functions of glands. 



(b) The work done in the mouth. 



(c) The work done in the stomach. 



(d) The work done in the small intestine. 



(e) The function of the liver. 



To discover the absorbing apparatus and how it is used. 



Laboratory Suggestions 



Demonstration of the food tube of man (with a manikin) . Comparison with 

 the food tube of the frog. Drawing (comparative) of the food tube and diges- 

 tive glands of frog and man. 



Demonstration of a simple gland. (Microscopic preparation.) 



Home experiment and laboratory demonstration. The digestion of starch by 

 saHva. Conditions favorable and unfavorable. 



Demonstration experiment. The digestion of proteins with artificial gastric 

 juice. Conditions favorable and unfavorable. 



Demonstration. An emulsion as seen under the compound microscope. 



Demonstration. Emulsification of fats with artificial pancreatic fluid. 

 Digestion of starch and of protein with artificial pancreatic fluid. 



Demonstration. Saponification, or making soaps from fats. 



Demonstration of tripe to show increased surface of the digestive tube. 



Laboratory or home exercise. Make a table showing the changes produced 

 upon the nutrients by each digestive fluid, the reaction (acid or alkaline) of 

 the fluid, where the fluid acts, and what results from its action. 



Purpose of Digestion. — We have learned that organic food 

 substances are found in the leaves of plants. This food must be 

 taken to other parts of the plant in order to be used. Before it 

 can be transported from one part of the plant to another, it is 

 changed by enzymes into a soluble form, so that it can pass from 

 cell to cell by the process of diffusion through a membrane. Much 



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