THE CIRCULATION 59 



onally and a knot tied in the middle. Opposite ends are 

 then tied, making a loose-fitting loop around the limb. 

 The knot is placed directly over the blood vessel to be 

 compressed and a short stick inserted in the loop. The 

 necessary pressure is then applied by twisting the hand- 

 kerchief with the stick. Time must not be lost, however, 

 in the preparation of a suitable bandage. The blood 

 vessel should be compressed with the fingers while the 

 bandage is being prepared. 



Summary. The blood, to serve as a transporting agent, 

 must be kept continually moving through all parts of the 

 body. The blood vessels hold the blood, supply the chan- 

 nels and force necessary for its circulation, and provide con- 

 ditions which enable materials both to enter and to leave 

 the blood stream. The heart is the chief factor in propel- 

 ling the blood, although the muscles and the elastic tissue 

 in the walls of the arteries and the valves in the veins are 

 necessary aids in the process. In the capillaries the blood 

 takes on and gives off materials, while the arteries and 

 veins serve chiefly as tubes for conveying the blood from 

 one system of capillaries to another. 



Exercises. i. Of what special value in the study of the body was 

 the discovery of the circulation of the blood? 



2. State the necessity for a circulating liquid in the body. 



3. Show by a drawing the general plan of the heart, locating and 

 naming the essential parts. Show also the connection of the large 

 blood vessels with the cavities of the heart. 



4. Compare the purpose served by the chordae tendineae to that 

 served by doorstops (the strips against which the door strikes in 

 closing). 



5. Explain how the heart propels the blood. To what class of 

 pumps does it belong? What special work is performed by each 

 of its divisions? 



6. Define a valve. Of what use are the valves in the heart? In 

 the veins? 



