50 Bacteria in Relation to Countnj Life 



edly affected not only by conditions more favorable 

 for their development, but, also, by the degree of ven- 

 tilation. Buildings whose air is renewed more frequently, 

 and whose windows allow a free access of sunshine, con- 

 tain fewer germs than similar buildings that are less 

 favorably situated. 



The dust of the city streets is very rich in bacteria. 

 It is natural to expect, therefore, that the air overlying 

 the streets will also be well stocked with them. An 

 examination of the air over the London streets showed 

 it to contain approximately from 300,000 to 500,000 dust 

 particles per cubic centimeter, while the corresponding 

 determination of the bacteria showed that there was 

 only one germ to every 38,300,000 dust particles. As 

 stated by Fischer, an examination of the street dust 

 in the city of Freiburg showed it to contain from 5 to 

 17 different species of bacteria included in from 24,000 

 to 2,000,000 germs per gram. 



This examination brought out the interesting fact 

 that the sprinkling of streets increases to a very marked 

 extent the number of bacteria in the dust. The sprinkled 

 streets contained a minimum of 1,450,000 germs, and 

 a maximum of 2,896,000 per gram of dust, while the 

 unsprinkled streets contained a minimum of 24,000 

 and a maximum of 48,000 germs. There is a difference, 

 not only in the number of germs in the sprinkled and 

 unsprinkled dust, but, also, in their resistance to the 

 destructive effect of drying. The less resistant forms 

 perished in the unsprinkled dust in four days, while, 

 in the sprinkled dust, they survived for fourteen days. 

 Fischer observes, with much justice, that the sprinkling 



