228 FIRST YEAR SCIENCE 



In order that all parts of the body may be provided 

 with the materials used in building their cells and in doing 

 the work necessary for continued existence there must be 

 a distributor}^ system. This is necessary wherever diver- 

 sified work is to be carried on. This necessity has brought 

 into effect the railway and canal systems of the world. 

 The body is a little world by itself, and it has a most com- 

 plete and wonderfully adapted system for supplying the 

 material needed and for removing the waste. The center 

 and motive power of this system is the heart. The medium 

 of circulation is the blood. 



When the blood is examined, it is found to consist of a 

 watery liquid, called the plasma, & great number of little 



disk -shaped bodies, the red cor- 

 puscles, and some irregular 

 " $ o whitish bodies, the white cor- 



puscles (Fig. 108). The white 

 corpuscles are protoplasmic cells 



GO?* o &>gj oo o'Jo having various functions and 

 o -o> oop o O QO o possessing the power of move- 

 o ment and even of working their 



Fi - way out of the blood vessels. 



The main function of the red 



corpuscles is to carry oxygen from the lungs to the different 

 living cells of the body. They contain a pigment, hcemo- 

 globin, which carries the oxygen and gives the blood its 

 color. The plasma, an exceedingly complex fluid, is com- 

 posed largely of water, but contains the nutrient and waste 

 materials supplied by the different organs of the body. 



The blood passes through different kinds of vessels. 

 Those leading from the heart are called arteries, and those 

 returning to the heart are called veins. As the arteries 

 proceed out from the heart they divide continually, becom- 

 ing smaller and smaller until they terminate in very small 



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