148 ELEMENTS OF WATER BACTERIOLOGY 



91 per cent of the 135 samples examined and grains 

 in 55 per cent of 300 samples. 



Colon Bacilli in Dust and Soil. Winslow and Kligler 

 (1912) have shown that colon bacilli may be very 

 abundant in the dust of city streets and houses, as 

 might naturally be expected from the fact that such 

 dust is largely made up of horse droppings. They 

 examined 24 samples of street dust and 72 samples of 

 house dust (all in New York City). All of the street 

 dusts and 63 of the 72 house dusts contained colon 

 bacilli in at least one of three duplicate i<U gram 

 portions. In two street samples the numbers rose to 

 330,000 and 660,000 per gram respectively, while the 

 largest indoor result was 60,000. The average for the 

 indoor dusts was between 1000 and 2000 per gram and 

 for the street dusts over 50,000 per gram. This dust 

 was dust deposited on surfaces and would only be 

 carried up into the air by currents of some force. It 

 is well known that colon bacilli are, as a matter of fact, 

 rarely present in street or house air. Konrich (1910) 

 exposed open Petri dishes of dextrose broth to the air 

 of Jena streets for 24-hour periods, daily, for 3 months 

 and found colon bacilli only n times. The colon 

 bacilli in street dust may, however, perhaps account 

 for the anomalous positive results sometimes obtained 

 in reservoirs bordered by roadways. 



Konrich (1910) has also made important contribu- 

 tions to the study of colon bacilli in the earth. Out 

 of 547 samples of soil, 65% showed B. coli in por- 

 tions of between .1 and .5 gm. The farther removed 

 from cultivation a sample was, the less were the chances 



