CHAPTER IV. 



CIRCULATION OF THE BLOOD. 



The Blood and its Work. If the supply of blood to 

 a muscle be shut off by tying or otherwise compressing the 

 arteries leading to it, the muscle soon loses its power to act. 

 If the blood supply is not too long checked, its readmission 

 will restore the muscle to normal condition. If the blood is 

 wholly shut off, say from one of the lower limbs, there would 

 soon be loss, not only of muscular power, but of sensibility as 

 well. 



We know that if any animal is bled freely, it becomes 

 weak, then unconscious, and soon dies, if the escape of blood 

 is 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. Our comfort, health, and often life itself, may de- 

 pend on our knowledge upon this subject. 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 inflam- 

 mations 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, 



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