THE BODY TEMPLE 45 



eye. Some of these are so small that more than a 

 hundred would be required to equal an ordinary pin 

 in size. 



Arteries and Veins.— There are two sets of these 

 tubes, one, called arteries, communicating with the 

 lower chambers of the heart ; the other, the veins, com- 

 municating with the upper chambers of the heart. 

 These two sets of tubes run side by side through the 

 various parts of the body, finally joining at the small 

 ends by means of very small tubes, the capillaries. 

 Thus they become, virtually, a single set of tubes, 

 which are large at the heart ends, and small in the 

 remote middle. 



The lower chambers of the heart pump the blood out 

 into the various parts of the body through the arteries ; 

 while the upper chambers receive it back through the 

 veins. The blood which leaves the left side of the heart 

 returns through the veins to the right side of the heart, 

 while the blood which leaves the right side of the heart 

 after passing through the lungs, returns to the upper 

 chamber of the left side. By means of openings 

 guarded by valves, the blood is enabled to pass from 

 the upper to the lower chamber on each side of the 

 heart, but cannot pass from one side to the other, ex- 

 cept by going the roundabout road of the arteries, 

 capillaries and veins. 



Six Quarts of Blood.— The arteries and veins of 

 a body of average size contain about twelve pounds, 

 or six quarts, of blood. If you wish to know something 

 about this wonderful fluid, you must thrust a pin into 

 the end of your finger, squeeze out a tiny drop, spread 

 it upon a slip of glass, and put it under a microscope. 

 Looking at it through the instrument, you will see that 

 it is no longer red, but of a light amber color, and on 



