2OO Physiology. 



all the particles are changed. But in the body the more 

 permanent parts change slowly. 



Nutrition. Nutrition includes all the changes that take 

 place in the body from the reception of food to the excre- 

 tion of the waste matter. It includes digestion, absorption, 

 circulation, assimilation, respiration (oxidation), and excre- 

 tion. The first four of these processes are stages in build- 

 ing up the tissues ; the last two are process of tearing doivn. 



We cannot destroy Matter. When a stick of wood is 

 burned it is no longer wood. But the matter is not de- 

 stroyed. It could all be obtained again from the smoke 

 and ashes. So, in the continual wasting away of our 

 bodies, there is no real loss of matter. Our weight is re- 

 duced, but the wastes are still part of the earth or the air, 

 and are of use in the world. We are as unable to destroy 

 matter as we are to create it. 



The Ceaseless Round of Matter. A particle of carbon 

 in the carbon dioxid of the expired breath may be taken in 

 by a blade of grass. A cow eats the grass, and we may 

 before long take the very same particle of carbon in the 

 milk or the flesh of the cow. Or the particle of carbon 

 may become part of a grain of wheat, and be made into 

 flour and be eaten as bread and be a part of the body 

 once more. Thus, there is a ceaseless round of matter 

 into and out of our bodies. No one has a monopoly of 

 any portion of matter ; it is now ours, now some one else's. 



We cannot create Force. We get our energy from the 

 food we eat, just as an engine gets its energy from fuel. 

 This is saying nothing against the superiority of the 

 human body and is not in the least degrading. We are 

 living, growing, self-directing, and self-maintaining ma- 



