336 



RESPIRATION AND EXCRETION 



of ventilation for the home is to place a board two or three 

 inches high between the lower sash and the frame of a window 

 or to have the window open an inch or so at the top and the 

 bottom. An open fireplace in a room aids in ventilation because 

 of the constant draft up the flue. 



Sweeping and Dusting. - - It is very easy to demonstrate the 

 amount of dust in the air by following the course of a beam of 

 light in a darkened room. We have already proved that spores of 



mold and yeast exist in 

 the air. That bacteria 

 are also present can be 

 proved by exposing a 

 sterilized gelatin plate 

 to the air in a school- 

 room for a few mo- 

 ments. 1 



Many of the bacteria 

 present in the air are 

 active in causing dis- 

 eases of the respiratory 

 tract, such as diph- 

 theria, membranous 

 croup, and tubercu- 

 losis. Other diseases, 

 as colds, bronchitis 

 (inflammation of the 

 bronchial tubes), and 



pneumonia (inflammation of the tiny air sacs of the lungs), are 

 also caused by bacteria. 



Dust, with its load of bacteria, will settle on any horizontal sur- 

 face in a room not used for three or four hours. Dusting and 

 sweeping should always be done with a damp cloth or broom, 

 otherwise the bacteria are simply stirred up and sent into the air 



1 Expose two sterilized dishes containing culture media ; one in a room being 

 swept with a damp broom, and the other in a room which is being swept in the usual 

 manner. Note the formation of colonies of bacteria in each dish. In which dish 

 does the more abundant growth take place ? 



Plate culture exposed for five minutes in a school 

 hall where pupils were passing to recitations. 

 Each spot is a colony of bacteria or mold. 



