CHAPTER VIII 

 THE CIRCULATION (continued) 



165. How the Heart is aided in its Work. The heart 

 seems to be constantly at work, but such is not the case. 

 As a matter of fact, the heart occupies nearly as much 

 time in resting as in working. It works for about half a 

 second and rests for about half a second. Yet it does 

 work in a day equivalent to raising a ton of coal nearly 

 two hundred feet. 



166. Increase the circulation in the arm by exercising it 

 for a few minutes. The veins in the front of the wrist will 

 then be plainly visible. The skin and walls of the veins 

 make the blood in the veins appear blue, but it is dark 

 purplish red. (Did you ever see "blue" blood?) Place 

 the tip of the forefinger on one of the large veins ; with the 

 middle finger then stroke the vein toward the hand so as 

 to push the blood from a portion of it, keeping the two 

 fingers in place. The vein remains empty between the 

 fingers. Lift the finger nearer the heart and no blood 

 enters the vein ; there is a valve above which holds it 

 back. Lift the other finger, and the vein fills instantly. 

 Stroke a vein toward the hand, and see the blood cause 

 the veins to swell up into little knots where the valves are. 

 (Experiments upon veins are plainest with adults whose 

 veins are large.) The veins have valves placed frequently 

 along their course. The valves are pockets made by a 

 fold in the inner coat of the wall of the vein (Fig. 93). 

 When you place your hand in your pocket, the latter 



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