CLEANLINESS IN BUTTER AND CHEESE FACTORIES. 129 



The bacteria content of well-water depends to a 

 large extent on its origin. If it comes directly from the 

 surface it will, especially during the hot season, be very 

 rich in bacteria, since surface-water generally goes through 

 fields, roads, and other places rich in bacterial life. In a 

 good many of our factories this danger of surface-water 

 leaking into the well has not been realized. Such water 

 may in several creameries run directly into the well or 

 down through the leaky woodwork; this explains why 

 many creamery-men complain that they cannot use the 

 well-water after a heavy rain. 



Even if the surface-water does not run into the well, 

 the water may contain bacteria in large number, according 

 to the stratum of the earth from which it is derived. 



The earth acts on the whole as a filter, retaining the 

 bacteria. We therefore find the largest number of such 

 organisms in its upper layers. In the surface layer of 

 sandy soil (in Berlin) Frankel found 45,000-350,000 bac- 

 teria per cubic centimeter, while Keimers in the surface 

 layer of a clayey soil (in Jena) found 160,000-2,500,000 

 per cubic centimeter; both investigators ascertained that 

 the largest quantity was not found directly on the surface, 

 but a little below the same a fact which is perhaps ex- 

 plained by the fatal action of the light on the surface bac- 

 teria. From maximum at a few inches below the surface 

 the bacteria content of the soil decreases rapidly as we go 

 down. Frankel found only 200-2000 bacteria in soil 

 three feet deep, and four and a half feet below the sur- 

 face the soil was generally free from bacteria. In Jena 

 absolute sterility of the soil does not appear until at a 

 depth of six feet. These facts corroborate the observation 

 made by both investigators mentioned, that the deep 



