HUMAN STRUCTURE AND LIFE-ACTIVITIES 465 



384. Foods are Combinations of the Nutrients. From 

 the foregoing experiments, it is evident that one or more 

 of the nutrients is present in each of the common foods. 

 Chemists have proved that the useful constituents of all our 

 foods are carbohydrates, fats, proteins, mineral salts, and 

 water. The above experiments also showed that some 

 foods have a preponderance of certain nutrients; e.g., white- 

 of-egg is chiefly protein, potato is chiefly starch, corn-syrup 

 is almost pure sugar, butter and beef-suet are largely fat. It 

 is evident that if all the nutrients are needed in human diet, 

 they can best be obtained by a mixture of foods ; that is, a 

 meal composed of lean meat, potato, bread, butter, and some 

 form of sugar might be arranged to supply equal amounts of 

 protein, fat, sugar, and starch. We shall see later that equal 

 amounts of these nutrients are not needed; but that a 

 mixture of foods is necessary in order to give the proper 

 amount of each of the nutrients of which our common articles 

 of food are composed. 



STRUCTURE OF HUMAN DIGESTIVE ORGANS 



In order to understand many points concerning the work 

 of the organs which deal with foods, we must first get a clear 

 idea of the general structure of the alimentary canal and of 

 its attached organs which secrete digestive fluids (liver, 

 pancreas, salivary glands). Therefore, we must for a time 

 turn aside from considerations of function and study the 

 structure of these organs. 



385. The Mouth-Cavity. (L) Turn your back to a window or 

 a lamp, and with a hand-mirror reflect the light into your open 

 mouth. Notice the hard palate forming the roof of the mouth- 

 cavity. At the back of the mouth-cavity is the soft palate, which 

 separates the mouth-cavity from the post-nasal cavity; and this 

 cavity in turn communicates with the cavities of the nose. Take 

 "short breaths" and notice the effect upon the soft palate. Apply 

 your tongue to the roof of the mouth and slowly move it backward 



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