414 FOODS CIRCULATED AND USED IN THE BODY 



be oxidized, so, combined with other elements into urea and 

 other wastes, it is eliminated through the kidneys. 



Laboratory Exercise. To study the skin as an organ of excretion 

 and of heat control. Examine the diagram of a cross section of skin. 

 Locate the epidermis, dermis, sweat glands, oil glands, nerves, and 

 blood vessels. 



Examine the surface of your skin with a hand lens. Where is the 

 epidermis and what structures does it contain? What structures 

 are found in the dermis ? 



Insert your hand in a clean, dry fruit jar. Wrap a towel over the 

 opening of the jar so as to allow no air to get in between your hand 

 and the sides of the jar. What happens in the jar? What is given 

 off from the hand? 



Weigh yourself. Note the weight. Exercise violently for half an 

 hour. Weigh yourself again. Note the weight. Was there any 

 change in weight? How must the change of weight have been 

 brought about ? Remember that when oxidation of food or tissue takes 



f place in the body, three prod- 



at least, 



organic 



are formed : 

 wastes, and 



anct 



ucts, 

 heat, 

 water. 



(Food + oxygen = carbon 

 dioxide + water + organic 

 wastes + heat + muscular 

 energy.) 



Take the temperature of 

 the body before and after 

 exercise by placing a clinical 

 thermometer in the mouth. 

 Account for any change in 

 temperature. 



What three substances are 

 given off from human bodies 

 that might affect the air of 

 a closed room? Are you 

 more comfortable on a hot 

 humid day or on a hot dry 

 day? Explain. 



The skin as an organ of 

 excretion. We have already 

 learned that the skin is an 

 organ of protection. Let 

 us now see how it aids in 

 excretion. The glands already studied form the excretion known 

 as perspiration, a watery solution containing little carbon dioxide, 



A sweat gland. Explain, with reference to the text, 

 where the water that is given off comes from. The 

 waste materials. 



