SOME PHYSIOLOGY YOU OUGHT TO KNOW 33 



The cells of the blood, however, have a great at- 

 traction for oxygen, consequently the cells absorb 

 oxygen with greediness, so that when the blood 

 returns to the heart it is fresh and bright and 

 ready to take its journey back over the body again. 

 This is done just about every three minutes. This 

 endless round continues until stopped forever by 

 death. 



The relation existing between the animal and 

 plant functions is brought to light in another way. 

 AVhen the plant was building tissue it released 

 oxygen and exhaled it into the air. At the same 

 time, by means of leaves, it gathered in the car- 

 bonic acid to use in plant building. Of course this 

 was got from the air. The animal in performing 

 its functions and in building its tissue inhales oxy- 

 gen from and exhales carbonic acid gas into the air. 

 Thus it is that animals take up what is unnecessary 

 to the plant and the plant uses what is waste and 

 poison to the animal. 



