2 24 How a Complex Animal Uses Food unit iv 



2. What is the composition of blood? Wash your hands in soap and 

 water. Sterihze the tip of one of your fingers bv washing it with alcohol. 

 Press the blood toward the tip and then prick it with a sterile needle. 

 Smear a drop of blood on a clean slide and cover with a cover glass. 

 Examine under low and high powers. What is the color of the blood as 

 you see it now? How do the corpuscles differ in appearance when they 

 are massed in the drop? What is the name of the substance in which the 

 red corpuscles are floating? Examine, if you can, a stained slide of blood. 

 What other type of cell do you now see? In what ways does it differ 

 from the red corpuscle? 



3. Do oxygen and carbon dioxide in blood change its color? Obtain 

 fresh blood from the slaughter house. To keep it from clotting add 10 cc 

 of a 2 per cent potassium oxalate solution to every 100 cc of blood. Let 

 it stand and observe. Then bubble oxygen through it. Does it change? 

 Now do the same with carbon dioxide. Does the blood lose its color? 



4. What is the structure of the heart? Examine a manikin or chart 

 showing the heart in its normal position. Where does it lie? If the chart 

 is carefully drawn, estimate the actual size of the heart. Examine a fresh 

 beef or lamb's heart, which is similar to yours. If necessary use chicken's 

 heart. In general, what is the color of the heart? Find the auricles; these 

 are the light-colored structures, shaped like bent ears, at the broad end 

 of the heart. Ask your teacher to help you distinguish the right auricle 

 from the left. How do auricles compare with ventricles in size? Feel the 

 auricles and ventricles. What do you notice? Explain. There is usually 

 fatty tissue along the line where left and right ventricles touch. Unless 

 the heart has been cut open when you buy it, make incisions (cuts) about 

 three inches long in the right and in the left ventricle. Compare the mus- 

 cular walls of the ventricles with those of the auricles. Compare the right 

 ventricle wall with the left. What differences do you note? How thick are 

 the walls of the blood vessels attached to the heart? Are they all the same 

 thickness? Insert a glass rod into each blood vessel to determine the 

 chamber with which it connects. Find the vessels which enter the heart 

 substance itself. Study the valves. Notice the flaps of tissue held do\\'n 

 against the sides of the ventricle by thin cords. These are the valves. When 

 the valves close, what position is taken by the flaps? WTiat effect would 

 this have on the blood which tends to go back into the auricles? 



5. Find and describe the tissue that forms the covering of the heart. 

 What is it called? You would probably be unable to separate this from 

 the tissues underneath. What kind of tissue makes up the walls of the 

 heart? Feel it and describe. If possible, examine some prepared slides of 

 heart muscle. How do these cells differ from voluntary muscle fibers? 

 How do they resemble them? This kind of muscle, called cardiac muscle, 

 is found onl\^ in the heart. Examine the inside lining of the heart. Does it 

 seem to be mucous membrane or serous membrane? Explain. In examining 

 the outside of the heart you saw fat tissue. And you know there must be 

 blood among the cells. Name at least five tissues that make up this organ. 



