HOW THE HUMAN BODY USES FOOD 



93 



about two days. Examine the contents of each tube. Did 

 digestion take place in tube A? In B? In C? In D? By 

 what two agents are proteins digested in the stomach? 

 Record the notes of this experiment in your notebook. 1 



Experiment 65. Is your heart a pump? 



Practice counting the beat of your pulse. Find the pulse 

 on the inside of your left wrist by placing the first finger 

 of your right hand across it. The pulse beat is caused by 

 the pumping of blood through the arteries by the heart. 



Salary Stand 



Vermiform Jfpendix 



Courtesy P. Blakiston's Sim 



FIG. 133. DIGESTIVE SYSTEM 



Using the second hand of a watch, practice counting the 

 number of heart beats per minute. How many times does 

 your heart beat a minute while you are standing up? 



Exercise vigorously for several minutes. What is the num- 

 ber of heart beats per minute just after exercising? 



Count the number of times you breathe a minute before 

 exercising. Count the number of times you breathe a minute 

 after vigorous exercise. Is there any relation between breath- 

 ing and heart action? 



In your notebook 2 record the notes of this experiment 

 and answer the questions. 



OTHER INVESTIGATIONS WHICH YOU CAN MAKE 

 1. Learn how to apply artificial respiration. 



1 See workbook, p. 34. 

 ' See workbook, p. 34. 



2. Make a study of patent medicines and their effect on 

 the human body. Collect clippings about them from news- 

 papers and magazines. 



READINGS WHICH WILL HELP ANSWER THE 

 PROBLEM QUESTIONS 



Most of the foods we eat cannot be used by our 

 bodies in their natural form because they are not 

 soluble. The foods will not dissolve, hence the human 

 body is not able to absorb and assimilate 3 them. The 

 process by which our bodies change foods into a sol- 

 uble form so that they can be absorbed by the body 

 cells is called digestion. 



How is our food digested? Food is taken into the 

 mouth, chewed, and then swallowed. It then passes 

 through the gullet to the stomach. From the stomach 

 it passes through the small intestines, then through 

 the large intestine. During this time the food is mixed 

 with various digestive juices which change insoluble 

 substances to soluble forms. See Figure 133. 



In the mouth the food is ground fine and mixed 

 with saliva secreted by three pairs of salivary glands. 

 Substances in the saliva change some of the starch 

 in the foods to sugar. By the act of swallowing, the 

 food passes into the gul- 

 let, a long tube that con- 

 nects the mouth with the 

 stomach. 



In the walls of the stom- 

 ach are small glands that 

 secrete gastric juice. Through 

 the action of muscles in the 

 walls of the stomach the 

 food is thoroughly mixed 

 with the gastric juice. The digestion of starch stops, 

 while the materials in the gastric juice begin the di- 

 gestion of proteins in the food. At intervals portions 

 of the partly digested food are forced out of the stom- 

 ach into the small intestine. 



In the small intestine the food is mixed with bile from 

 the liver, pancreatic juice from the pancreas, and in- 

 testinal juices secreted from the walls of the intestine. 

 These digestive juices complete the process of diges- 

 tion. The starch and proteins are further acted upon 

 and the fats are also digested. All undigested ma- 

 terials pass into the large intestine and are expelled 

 from the body as waste matter. 



How can we keep our digestive system in good 

 working order? Retaining food in the mouth and 

 chewing it well is beneficial to digestion. Small pieces 

 of food particles are more easily acted upon by the 



'Assimilate, to convert nourishing material into the fluid or 

 solid substance of the body. It is the last stage in the process of 

 nutrition, following after digestion. 



\ 



FIG. 134. CROSS SECTION 

 OF INTESTINE 



