300 



DIGESTION AND ABSORPTION 



starch paste, saliva, and a few 

 drops of any weak acid, the starch 

 will be found not to have changed. 

 The digestion or change of starch 

 to grape sugar is caused by the 

 presence in the saliva of an enzyme, 

 or digestive ferment. You will re 

 member that starch in the grow 

 ing corn grain was changed to 

 grape sugar by an enzyme called 

 diastase. Here a similar action is 

 caused by an enzyme called ptyalin. 



Experiment showing non-osmosis of This ferment acts only in an alka- 

 starch in tube A, and osmosis of line medium at about the tempera- 



sugar in tube B. Q th 



Mouth Cavity in Man. 

 In our study of a frog we 

 find that the mouth cavity 

 has two unpaired and four 

 paired tubes leading from 

 it. These are (a) the gullet 

 or food tube, (b) the wind 

 pipe (in the frog opening 

 through the glottis), (c) the 

 paired nostril holes (pos 

 terior nares), (d) the paired 

 Eustachian tubes, leading to 

 the car. All of these open 

 ings are found in man. 



In man the mouth cavity, 

 and all internal surfaces of 

 the food tube, are lined 



With a muCOUS membrane. T he mouth cavity of man. e, 



The mucus secreted from tube; h P> hard palate; 8 p, sott paiate; 



ut, upper teeth ; be, buccal cavity ; k, lower 



It 



gland cells in this lining 

 makes a slippery surface so 



teeth ; /, tongue ; ph, pharynx ; ep, epiglot 

 tis ; Ix, voice box ; oe, gullet ; tr, trachea. 



