222 'THE HUMAN BOLT. 



feet. The work done daily by the ventricles of the heart 

 together is equal to that required to raise one pound 434,112 

 feet from the earth's surface, or, what comes to the same 

 thing, more than 193 tons one foot high. 



If a man weighing 165 pounds climbed up a mountain 

 2644 feet high the muscles of his legs would probably be 

 greatly tired at the end of his journey,, and yet in lifting 

 his body that height they would only have done as much 

 work as his heart does every day without fatigue in pump- 

 ing his blood. 



No doubt the fact that more than half of every round 

 of the heart's activity is taken up by the pause during 

 which its muscles are relaxed and its cavities filling with 

 blood, has a great deal to do with the patient and tireless 

 manner in which it pumps along, minute after minute, 

 hour after hour, and day after day, from birth to death. 



The Pulse, When the left ventricle of the heart con- 

 tracts it forces on about six ounces of blood into the aorta, 

 which, with its branches, is already quite full of blood. 

 The elastic arteries are consequently stretched by the extra 

 blood, and the finger laid on one feels it dilating; this dila- 

 tation of an artery following each beat of the heart is called 

 the pulse; it is easiest felt on arteries which lie near the 

 surface of the body, as the radial artery, near the wrist, 

 and the temporal artery, on the brow. 



The arteries at their ends furthest from the heart lead 



How much both ventricles together? 



How high would a man have to climb in order to do as much 

 work by the muscles of his legs as the heart does in a day? 



How may we account for the fact that the heart does not become 

 fatigued and unable to work? 



What happens when the left ventricle of the heart contracts? 

 What results in the arteries? What is the pulse? Name arteries or 

 which the pulse is easily felt. 



