PROBLEM 201 235 



tube from a stoppered bottle containing a little piece of oxone 

 (which gives off oxygen) into the second tube. 



Observations. Note the change of color in both test tubes. 

 The change from a deep purple to a scarlet occurs in the lungs 

 as blood passes through them. 



Conclusion. 1. How can we know of the presence of oxygen 

 in the blood? Of carbon dioxide? 



2. How and when would carbon dioxide get into the blood? 

 (Remember the cells of the body do work.) 



NOTE. The red corpuscles contain a substance known as haemoglobin which 

 readily unites with oxygen. When the corpuscles take up oxygen, their color 

 changes to a brighter red. 



3. How is the oxygen carried in the blood ? 



Problem 2O1 : To study the structure of the heart. 



Materials. Model of a human heart, beef heart (opened), 

 and charts. 



Method. Refer to chart of circulation, page 321, Civic Biology. 

 Find the heart, arteries, and veins connected with it. Find out 

 where the chief arteries lead and from where the large veins 

 come. Also examine a beef heart or a good model and note the 

 four chambers, the valves, and the blood tubes leading to and 

 from it. 



NOTE. The upper chambers (see model) are called the right and left auricles 

 respectively ; the lower chambers the right and left ventricles. 



Observations. Which have the thicker walls ? What is prob- 

 ably the use of these walls ? Notice the position of the valves and 

 the direction of their movement. In what direction do arteries 

 lead? Veins? Into how many chambers is the heart divided? 

 Do these chambers all connect with one another? Can you find 

 a solid wall between the right and left sides? Can you show the 

 heart to be a double force pump? Where does the right side of 

 the heart send the blood? The left? 



Conclusion. Write a paragraph describing the structure of 

 the heart. 



Drawing. Make a drawing from the model. Label all parts. 



