SOME PHYSIOLOGY YOU OUGHT TO KNOW 29 



If in the former, it is carried to the thoracic duct, 

 which extends along the spinal column and enters 

 one of the main blood vessels. If collected by the 

 capillary system, it is carried to the portable vein, 

 thence to the liver and finally to the heart, where 

 it meets with the blue blood collected from all parts 

 of the bod} 



At this point, the blood contams both the nutri- 

 ment and the waste matter of the body. Before it 

 can be sent through the body again the waste ma- 

 terial must be thrown out of the system by means 

 of the lungs. This is accomplished by the heart 

 forcing to the lungs the impure blood with its im- 

 purities collected from all parts of the body and 

 also the nutriment collected from the digestive 

 tract. 



The chief organs, therefore, of the circulatory 

 system are the blood and lymphatic vessels contain- 

 ing respectively blood and lymph. The only dif- 

 ference between these two materials is in the fact 

 that lymph is blood without the red-blood corpuscles. 

 The body, after all, really depends upon this lymph 

 for nourishment, since it wanders to all parts of 

 the body, surrounds all the cells in all of the tissues 

 and in this way carries to the cells the very kinds of 

 food that they need. 



Lymph Passes Through Cell Walls. — The blood 

 vessels have no openings into the body at all. In 

 this respect the blood system is like the digestive 

 system ; it is separate and distinct in itself. The 

 blood, however, does creep through the walls of the 

 blood vessels. In so doing the blood corpuscles 

 are left behind and lymph is the result. 



The center of the blood system is the heart. It 

 is the engine of the body. Going out from it is the 

 great aorta, which subdivides into arteries and 



