44 PLAIN FACTS FOR OLD AND YOUNG 



opecl; and how they become diseased when not properly 

 exercised is considered elsewhere in this work. 



A Live Pump.— Place your hand upon the left side 

 of the chest, just above the lower border of the ribs. 

 You feel something which goes thump, thump, thump. 

 Get a friend to let you place your ear upon his chest 

 at the same spot. You hear something saying lub-tup', 

 ]ub-tup'. There is a live pump in there, the heart, 

 which keeps working away all your life, from infancy 

 to old age, making sixty to seventy strokes every min- 

 ute, never stopping to rest even for five seconds, though 

 sometimes it becomes tired and flags a little, and at 

 other times gets excited and runs away at a frightful 

 rate, sometimes so fast one can scarcely count it. 



The heart, as already stated, is a hollow muscle. 

 A man has a little more heart than a woman. His 

 heart weighs about ten ounces, while a woman's heart 

 weighs but eight. Roughly estimated, the heart may 

 be said to be as large as the fist. A man with a big fist 

 has a large heart to furnish the brawny arm with an 

 abundance of blood. The heart of a whale is as large 

 as a wash-tub, while that of some small creatures is 

 microscopic in size. 



The Two Hearts. —The heart has a partition 

 through the middle, the longest way, which divides it 

 into halves, each of which is again separated into 

 two chambers. Each side of the heart may be con- 

 sidered as a distinct heart. In some lower animals, as 

 a dugong, the two sides are connected only by a band 

 of tissue. Some insects have three or four hearts. The 

 cavities of the heart are connected with every part of 

 the body by means of a set of tubes, which at the heart 

 are as large as the thumb, but by subdivision become 

 so minute in the tissues as to be invisible to the naked 



