246 



RESPIRATION AND EXCRETION 



In which dish has the greatest number of colonies developed? 

 Conclusion. 1. In which room was the most dust (and 

 bacteria) stirred up? 



2. What do you consider the best method of cleaning a room? 



Problem 217 : What makes a crowded, closed room uncom- 

 fortable? 



NOTE. It has recently been discovered that other factors besides the presence 

 of carbon dioxide in the air of a room make it uncomfortable. A little thought on 

 the following questions will convince you of this. 



Observations. When a candle burns, what is given off be- 

 sides carbon dioxide? When a number of people are in a closed 

 room, what then would be given off from their 

 bodies ? 



NOTE. The use of a wet and dry bulb thermometer 

 in a closed room containing people will show a decided in- 

 crease in the water content (humidity) of the air. 



Where does this water come from? In 

 what condition does it get into the air ? 



What is your normal temperature ? Is that 

 the temperature of the air of the room? 

 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? 

 What similar condition exists in a closed 

 room? 



A WET AND DKY 

 BULB THERMOMETER. 



NOTE. The close odor noticeable in a closed room 

 containing people is due to certain organic wastes given 

 off from the body into the air. 



Conclusion. What factors cause discomfort in closed rooms 

 where there are many people? 



Problem 218 : To study the structure of the kidney. 

 Material. A sheep kidney. 



Method and Observations. An idea of the internal structure 

 of the kidney of man may be gained by examination of a sheep's 



