MICROORGANISMS IN WATER. 199 



With a yearly rainfall of 609 . 6 mm. (24 in.), the rain washes down during 

 the year some five million organisms to the square yard. 



SNOW. The results obtained from snow are similar to those ob- 

 tained from rain; but as a rule the numbers are larger, a result doubtless 

 due to the larger particles of the snow flakes. One investigator has 

 found from 334 to 463 bacteria per c.c. of snow water. On the summit 

 of high mountains snow is practically sterile, Binot not finding a single 

 organism in 8 c.c. of water from mountain-top snow. 



Water issuing from glaciers is of remarkable purity, containing only 

 from three to eight organisms per c.c.; but the numbers are larger as the 

 distance from the glacier increases. 



HAIL. Hail stones usually contain large numbers of bacteria, vary- 

 ing from 628 to 21,000 per c.c. of water obtained from the melting hail. 

 Fluorescing bacteria have been found in some samples; and the presence 

 of these microorganisms suggests that surface water is sometimes carried 

 up by storms and congealed. The presence of many molds in hail is 

 due to contamination from the air. 



DEEP WELLS. Deep well water and spring water contain as a rule 

 but few organisms, usually less than 50 per c.c. on gelatin at 20, and 

 less than 5 per c.c* on agar plates at blood heat. In a series of tests of 

 water taken direct from forty-three artesian wells, 1*52.4 M. (500 feet) 

 deep or more, the writer has found an average of 27 per c.c. for the 

 gelatin and 1.5 per c.c. for the agar counts. These tests have extended 

 over a period of several years; and water from deep springs has given 

 similar results. 



SHALLOW WELLS. The bacterial content of shallow wells depends 

 greatly on their location and construction. Even in those well located 

 and constructed, the number varies with the amount of rain fall, and 

 is often large. In polluted wells, very high numbers of organisms are 

 found. 



Sedgwick and Prescott found from 190 to 8,640 bacteria per c.c. in 

 unpolluted wells. 



In the same class of wells, Savage found from 10 to 100 per c.c. by 

 the blood-heat count, and 100 to 20,000 or more by the gelatin count. 



Sixty polluted wells examined by the writer gave an average gelatin 

 count of 740 bacteria per c.c.; and thirty-eight wells which were free of 

 contamination gave an average count of 400 per c.c. 



Polluted wells often give counts approximating the higher numbers 



