200 RESPIRATION, BLOOD, AND EXCRETION 



carried by the plasma, although some of it unites with the 

 haemoglobin. 



White blood corpuscles are much like the amoeba in 

 that they are colorless and can change their form. They 

 move about in the body and often leave the blood vessels 

 and collect at one place to aid the body in destroying 

 disease germs. 



The blood plasma is straw-colored and varies in compo- 

 sition from day to day, and hour to hour. It contains the 

 foods on their way to the cells and waste products on their 

 way to the kidneys, lungs, or skin. 



The volume of blood in the average person is about six 

 quarts. 



When exposed to the air, blood forms a clot, because of 

 the presence of a substance (fibrinogen) which produces 

 fibers that hold the red and white corpuscles. 



Student Report on Blood 



Name of Animals 



03 



159. Heart and Blood Vessels. — The blood is carried 

 from the heart to all the cells of the bodv and back to the 

 heart again and again. The heart serves as a pump to 

 force the blood along. The heart is about the size of 

 the fist and has strong muscular walls. In a healthy 

 person, it contracts regularly about seventy times a min- 



