CHAPTER IV. 

 CIRCULATION OF THE BLOOD. 



The Blood and its Work. We know that if any animal 

 is bled freely, it soon becomes weak, then unconscious, and 

 soon dies, if the escape of blood be not stopped. 



We observe the natural difference in color of different 

 parts of our bodies ; for instance, the lips and cheeks. 

 We often note varying color, as in blushing and pallor. 



We wish to understand these differences and changes ; 

 also to know what to do in case of fainting or bleeding 

 from wounds. We may prolong and make more useful 

 our own lives and those of others by knowing, in a practical 

 way, something about the causes, prevention, and remedies 

 of the colds, congestions, and inflammations to which we 

 are subject. 



Nearly every part of the body bleeds when cut. There 

 is no bleeding when we trim the nails or cut the hair, and 

 the outer skin has no blood in it. But the inner skin, and 

 almost every tissue within it, if pierced even by the finest 

 needle, yields blood. We see a little blood oozing from 

 the surface of a fresh steak or roast. 



What kind of a substance is the blood ? Is it uniformly 

 distributed through the tissues, like water soaked up into a 

 cloth, or is it in distinct cavities ? Why is it so essential to 

 life ? How does it do its work ? 



The Rate of the Heart Beat. The heart beats about 

 seventy-two times a minute in men ; in women, about 



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