CLEANLINESS IK BUTTER AND CHEESE FACTORIES. 133 



in dairy work must be spoken of a little more at length. 

 Many investigators have proved that ice may contain a 

 large number of bacteria. Frankel found ice from the river 

 Spree to contain between 20 and 6000 bacteria per cubic 

 centimeter. Ice from rivers and lakes close by cities and 

 factories will contain a large number of bacteria; conditions, 

 as whether the ice sampled was formed near by the shore or 

 out in the open lake, at the surface or farther down, will also 

 cause great variability in the results found by analysis. 



Bacteria in Ice. Although we may find a considerable 

 number of bacteria in ice under certain conditions, it is, 

 however, a fact that every time water freezes its bacterial 

 content is considerably diminished. FrankeFs investiga- 

 tions show this plainly. Water from the river Spree 

 containing 6000 bacteria per cubic centimeter froze at 

 10-18 F. After two days one cubic centimeter con- 

 tained only 1200 bacteria, and after nine days only 14. In 

 another sample 3300 bacteria were found per cubic centi- 

 meter at the beginning of the experiment and after three 

 days' freezing only 20 bacteria in the same volume. A 

 third sample, which was highly infected with bacteria, con- 

 taining not less than 500,000 bacteria per cubic centimeter, 

 showed only 36,000 per cubic centimeter after six days' 

 freezing. The freezing is therefore a powerful means 

 against the development of the bacteria in the water.* It 

 is in reality of no great importance that absolute sterility 

 cannot be obtained in the water in this way, as the bacterial 

 content by this method will be extremely small, provided 

 the water is not highly infected before the freezing. 



In the bacteriological analysis of ice which I have 

 made I have obtained greatly varying results, according to 

 * See foot-note on p. 134. 



