DUST AND ITS DANGERS. 2$ 



ious places in New York on a clear, dry, mod- 

 erately breezy day, in April, 1890. Each one 

 of the spots represents a colony of bacteria, 

 which has grown from the single germ which 

 settled on to the moist surface during the five 

 minutes exposure to the air. 



1. Ball Ground, Central Park. A mod- 

 erate westerly wind bringing dust over from 

 the Eighth Avenue and its cross streets. 



2. Union Square. At the edge of the 

 fountain basin. 



3. The library of a private house not far 

 from 34th Street and Broadway. 



4. A large retail dry-goods store on one of 

 the uptown cross streets near Broadway, during 

 a busy hour of the day, when there was much 

 stir and bustle. 



5. Railing of the small park at Broadway 

 and 35th Street. 



6. A cross street through which the carts of 

 the Street-Cleaning Department were passing 

 collecting the dry heaps of street dirt. 



If we translate into numbers the appearances 

 of the cultures shown in Plate III., we find that 

 during five minutes the number of living germs 



