CHAPTEP XIII. 

 BLOOD AND LYMPH, 



Why we need Biood. Some very small animals of simple 

 structure require no blood; every part catches its own food 

 and gives off its own wastes to the air or water in which 

 the creature lives. When, however, an animal is larger and 

 more complex, made up of many organs, some of which are 

 far away from, the surface of its body, this is impossible; 

 some organs are therefore set apart to catch food, and 

 arrangements made to carry some of this food to the others. 

 In our own bodies many parts lie faraway from the stomach 

 and intestines which receive, digest, and absorb our food, 

 and from the lungs which take oxygen gas out of the air 

 we breathe; yet every part, bone and muscle, brain and 

 nerve, skin and gland, needs a steady supply of both of these 

 things to keep it alive. The division of labor, in accordance 

 with which some organs are especially set apart for the 

 purpose of receiving substances from the outside world 

 to build up, nourish, and repair the body, necessitates 

 an arrangement by which the matters received shall be 

 distributed to other parts. This distribution is accomplished 

 by the blood, which flows into every organ from the crown 

 of the head to the sole of the foot. Being pumped round 



What kind of animals do not need blood? How are their want* 

 supplied and their wastes removed? Why do we find special recep- 

 tive organs in larger animals? Illustrate from the human body,, 

 What arrangement is necessitated by the fact that special organs are 

 set apart in the body for receiving food and oxygen? How is the 

 distribution effected? 



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