244 How a Complex Afiimal Uses Food unit iv 



2. How much variation is there in the temperature of a normal healthy 

 body? Take your temperature after strenuous exercise. If possible take 

 your temperature at some time when the atmosphere is cold and you are 

 feeling chilly. How much difference do you note? How can you explain 

 your observations? 



3. What part of SM^eat remains on the skin? Using an evaporating dish, 

 heat water in which are dissolved small amounts of salts such as are com- 

 monly excreted by the human body (sodium chloride and calcium chlo- 

 ride). Continue until all the water has disappeared. What is left? Have 

 you used a control? What is constantly happening on a small scale on the 

 surface of your body? Can you explain why it is desirable to clean the 

 skin with soap and warm water every day? 



4. How does evaporation affect the temperature of an object? Use 

 three thermometers with equal temperature readings. Wrap the bulb of 

 each with a small piece of cotton. Either absorbent cotton or cotton cloth 

 will do. Hang up the three thermometers side by side about three inches 

 apart. With a medium dropper put a drop of alcohol on one bulb and a 

 drop of water on another. After two minutes add another drop of alcohol 

 and of water. Leave the third dry. Read the temperatures. Explain the 

 differences in the readings. 



5. The answers to all the following questions grow out of your under- 

 standing of the paragraph you have just read. Remember that rapid evapo- 

 ration cools you much more than slow evaporation, (a) What might be 

 the danger of going right out after a hot bath on a cold day? Explain. 

 (Hint: What effect does heat have on the blood supply to the skin?) (b) 

 What is the advantage of a cool shower after a hot bath? (c) What might 

 be the danger of sitting in a strong cool breeze after vigorous exercise has 

 made you hot? (d) Why is so much more discomfort felt on a warm 

 "muggy" day than on a warm dry day? (e) Is an electric fan of any real 

 benefit or does the user merely imagine that it helps him? 



6. Summarize your information by formulating as many rules as you 

 can think of for keeping cool on a hot day and keeping warm on a cold 

 day. Give your reason for each. 



7. What is an important function of the skin besides regulation of body 

 temperature? As you sit still at your desk, close your eyes and move 

 your hand until it touches something on your desk. What did it touch? 

 How did you know? Examine Figure 236 for some structure which makes 

 it possible for the skin to do this. 



Further Activities in Biology 



I. How can you measure the percentage of moisture in the air of your 

 room? Construct a wet and dry bulb thermometer. This piece of ap- 

 paratus consists of two thermometers, one of which has a thoroughly wet 

 piece of cotton cloth wrapped around its bulb. If the air can hold more 

 moisture, water will evaporate from the wet bulb thermometer, and its 



