HOW DIGESTION TAKES PLACE 



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know. This is an organ of much harm and little use, because 

 of the disease appendicitis which results from its inflam- 

 mation. 



How digestion takes place. It is not so easy for us to 

 understand how solid foods are made liquid in the food 

 tube, but perhaps the following experiments will help. 

 If we take unsweetened cracker and chew it for some time, 

 we notice it begins to taste sweet. A cracker is composed 

 largely of starch. 

 Mix some powdered 

 cracker, or starch, 

 with a small quantity 

 of water. Pour this 

 mixture into a fun- 

 nel lined with filter 

 paper, and allow the 

 substances to trickle 

 through into a test 

 tube. Take grape 

 sugar of equal weight 

 with the starch. Mix 

 with as much water as before and filter in like manner. 

 We can prove that no starch comes through the filter. If 

 we test the water that drips through with iodine, it does 

 not turn dark blue. If we taste the water which has 

 dropped through from the funnel containing the sugar, 

 we find it is sweet. Evidently sugar passes through 

 this wall, while starch does not. An experiment per- 

 formed with unsweetened crackers shows that mixing a 

 cracker thoroughly with saliva causes some of the starch 

 to change to grape sugar (a kind of digested starch) while 

 cracker moistened with water will not be changed. This 



What does this experiment prove ? 



