CHAPTER VI. 



EXCRETION. 

 THE SKIN AND ITS FUNCTIONS. 



WE have seen that the energies of the body heat and 

 motion are produced by the oxidation in its tissues. Dur- 

 ing this oxidation waste products are formed, which if retained 

 in the body would cause very injurious effects. 



How does the 



body get rid Of Sweat Pore 



these substances ? 

 We have already 

 learned that the 

 lungs throw off 

 carbon dioxid, 

 water, and cer- 

 tain putmscible 

 organic matter. 



The skin is 

 constantly throw- 

 ing off wastes, 

 collectively called 

 Sweat, or perspi- 

 ration. Let us first 

 study the struc- 

 ture of the skin. 



The Structure of the Skin. The skin has two layers, 

 the inner, or Dermis, and the outer, or Epidermis. A bruise 



151 



Hair 

 Bulb 



Fig. 50. Vertical Section of the Shin. 



