Circulation, Assimilation and Excretion 425 



out the body, after the blood has delivered the nutrient to the 

 cells. Each cell of the body takes up a bit of this food and trans- 

 forms it into a substance similar to itself. In this way the body 

 of a growing child increases in size. Some of the digested 

 food is immediately oxidized in the blood, producing heat 

 energy. 



Sugar in the form of glucose and protein in the form of pep- 

 tone are carried directly to the 

 liver after absorption from the 

 intestines, reaching this organ 

 through the portal vein. As the 

 blood leaves the liver it con- 

 tains a small amount of glucose 

 which is quickly oxidized in the 

 blood, producing heat energy. 

 Peptone, on reaching the liver, 

 undergoes certain changes. 

 Some of it is oxidized, but the 

 greater part is carried in the 

 blood current to the cells of the 

 body, where each cell assimilates 

 as much as is needed for its 

 growth and repair. 



Excretion. Excretion is 

 the process of throwing off the 

 waste substances of the body. 

 These substances consist of 

 water, carbon dioxide, urea, 

 mineral matter and undigested 

 material. All wastes except un- 

 digested material are primarily 

 excreted in solution from the 

 cells of the body by osmosis. 

 They pass into the blood current and are carried to the different 

 organs of excretion. 



The organs of excretion are the kidneys, the skin, the lungs, 

 the liver and the large intestine. 



THE KIDNEYS AND THE BLADDER 

 They eliminate waste. 



