To view the digestive structures, open on the ventral side to expose the diges- 

 tive organs in their normal position within the body. Note the relative arrange- 

 ment of the liver, stomach and intestines. Also, note the fine connective tissue 

 carrying blood vessels, which connects with the folds of the small intestine and 

 holds them in position. Beginning at the anus, cut out the intestinal tract of each 

 of the animals and sever connective tissues so that the intestines may be stretched 

 out full length; compare the organs in the several animals. 



8 To show the effect of pancreatic enzyme on fat, place a few drops of feebly 

 alkaline emulsion of olive oil containing blue litmus upon a microscope slide, and 

 add a little pancreatic juice. Under the microscope note that the tissue becomes sur- 

 rounded by a red halo. This shows a formation of acid; it is due to the fatty acids 

 set free from the fat by the enzymes present. 



QUESTIONS 



1 Why cannot the cells of our body make use of the food as we receive it 

 from the kitchen.? 



2 What kind of nutrient is digested by the mouth juices? 



3 Why is it necessary to chew food that is not digested by the mouth juices? 



4 How can plants, which have no stomachs, digest food? 



5 How can we show that saliva acts upon starch but not upon protein? 



6 In what respects are enzymes like vitamins? In what respects are they 

 different ? 



7 How do digested nutrients reach the body cells? 



8 How are undigested portions of food moved along through the food tube ? 



9 What glands secrete digestive juices, and what effects are produced by 

 each juice? 



10 What functions other than digestion do gland products carry on in the 

 body? 



11 In what ways are the digestive systems of various animals especially 

 adapted to digesting distinctive kinds of foods? 



12 What makes plant tissues, as a rule, harder to digest than animal tissues? 



13 How is it possible for a person to live after a surgeon has removed his 

 stomach ? 



14 How are various species able to survive on an intermittent food supply? 



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