3i6 



MICROBIOLOGY OF WATER AND SEWAGE 



source than those of typhoid fever, owing to the "explosive" character 

 .of the disease. At the time of the outbreak of cholera in Hamburg, in 

 1892, the cholera vibrios were frequently isolated from the water of the 

 river Elbe, which was used to furnish the regular supply of the city. 

 The adjoining city of Altona also obtained its water from the same 

 river, after it had received some of the Hamburg sewage; yet it remained 

 practically free from the scourge, owing to the efficiency of sand filters 

 which were used to purify the water (Fig. 122). In times of epidemic, 

 the organism has been isolated from rivers, wells, and reservoirs in 

 India, a country in which the disease is endemic. 



THE NUMBER OF BACTERIA IN RAIN, SNOW, HAIL, ETC., AND IN WATER 

 FROM WELLS, UPLAND SURFACE WATERS, RIVERS, AND LAKES 



RAIN. The number of bacteria found in rain depends upon the 

 month of the year and the dryness of the air. When considerable dust 

 is present in the air, the first rain beats it back to the soil; and at 

 such time rain water contains more organisms than usual. Rain falling 

 in densely inhabited cities always contains more microbes than rain 

 falling on open farm land or upland pastures. A few figures will be 

 sufficient to illustrate. 



NUMBER OF BACTERIA PER LITER OF RAIN WATER 

 Figures for Montsouris Park, Paris, France, and the average for two years 



Yearly average 5,300 per liter per month. 



The average for the interior of Paris corresponds with the larger 

 amount of dust in the air, and reaches a total of 19,000 organisms per L. 

 With a yearly rainfall of 609.6 mm. (24 inches), the rain washes 

 down during the year some 5,000,000 organisms to the square yard. 



