418 



GENERAL SCIENCE 



warn 



Street Cleaning. A number of diseases may be trans- 

 mitted by means of the floating particles with which the 

 city air is charged. Air may be tested for disease-pro- 

 ducing bacteria by making a gelatin and agar culture of 

 whatever things are floating in the air. There are many 

 sources of dust in the city. The chimneys pour out some 



of it ; the traffic on 

 the streets gradually 

 grinds loose material 

 into particles that are 

 small enough to be car- 



^ SBf--* * r * ec ^ ky the wind ; and 



J * the decomposition of 



4* refuse of all sorts pro- 

 1 duces dust. The best 

 method of preventing 

 the spread of diseases 

 whose germs float in 

 the air, and eliminat- 

 ing obj ectionable street 

 odors is a thorough 



system of street cleaning (Figure 369). The streets should 

 be swept at short intervals and all refuse carted away. 

 Once each week the street should be washed clean by 

 " flushing" it. 



Garbage, Ashes, and Rubbish. --These wastes should 

 be placed in different receptacles at the homes so that 

 they may be collected most economically. Many modern 

 cities are now burning their garbage and rubbish. 

 This is an ideal way of disposing of it from a sanitary 

 standpoint. Ashes may be used for making desired 

 fills near the city. New York is building Rikers Island 

 with her ashes and street sweepings. The garbage is 



FIG. 369. A Street Cleaner. 



