406 Our Surroundings 



tubes add saliva and shake the contents. Place both test tubes in 

 a pan of water at 98.5 Fahrenheit for ten or twelve minutes. 

 Remove both tubes from the water, add Fehling's solution to each 

 tube, and then heat. Observe results. 



To Show the Digestion of Protein. Place a small piece 

 of the white part of a boiled egg in a test tube containing a solu- 

 tion of pancreatin or pepsin and close the open end of the tube 

 with absorbent cotton. After shaking, leave the tube with its con- 

 tents for a few hours in a room at about normal body tempera- 

 ture. For a control, prepare a second tube in the same manner, 

 using water instead of a solution of pancreatin or pepsin, and set it 

 aside under the same conditions and for the same length of time 

 as the first tube. 



Observe that the piece of protein in the first tube has dis- 

 appeared. It has dissolved, that is, has been digested. Why did 

 the piece in the second tube not dissolve? 



To Show the Digestion of Fat. Place a small amount of 

 olive oil in a test tube containing a solution of pancreatin and 

 close the open end of the tube with absorbent cotton. After shaking 

 the tube with its contents thoroughly, set it aside for a short time. 

 For a control, prepare a second tube in the same manner, using 

 water instead of a solution of pancreatin. After shaking, set it 

 aside with the first tube. 



Observe that in the first tube an emulsion has been formed, 

 that is, the fat particles have been separated and the contents have 

 a milk-like appearance. A similar effect is produced by digestive 

 fluids on fatty food in the intestine, rendering it soluble. Observe 

 what happened in the second tube and account for the different 

 result. 



SUMMARY 



Digestion is the process by which the food we eat is so 

 changed that the nutrient substances can be absorbed into the 

 blood. 



The most important parts of the alimentary canal are the mouth, 

 the pharynx, the esophagus, the stomach, the small intestine, and 

 the large intestine. 



