CHAPTER XIII. 

 EXCRETION. 



The Formation of Waste Matter in the Body. All the 



force, or energy, of the body is produced by oxidation in 

 the tissues; thought by oxidation in the brain; motion by 

 oxidation in the muscles; and heat wherever oxidation 

 goes on. This oxidation produces waste matter in our 

 bodies just as we have seen that oxidation in a stove 

 produces waste matter. 



The Need of Removal of Waste. When we waken on a 

 cold winter morning we are likely to find that the fire in 

 our hard coal stove has burned low. Not enough heat is 

 given out. What is the trouble? Is it merely that more 

 coal is needed ? We put another hod of coal in the maga- 

 zine (though usually some remains). Does this bring the 

 desired result ? No. We open the draft. Is this suffi- 

 cient ? It is not. We must shake down the grate and 

 clean out the clinkers. The removal of waste is as neces- 

 sary as the addition of a fresh supply of fuel. In this case 

 more necessary, for no amount of fuel will do any good so 

 long as the ashes shut off the draft. In our bodies the 

 removal of waste is still more important, because waste 

 matter not only clogs the system, but, if present in any 

 great amount, acts as a poison to the tissues. 



The Skin throws off Waste Matter. The skin is 

 constantly throwing off waste matter called sweat, or 

 perspiration. 



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