98 Bacteria in Relation to Country Life 



variable number of bacteria, depending on the purity 

 of the water employed. 



Bacteriological examinations of thick cakes of natural 

 ice have shown that, as the freezing proceeds from the 

 top downward, the number of bacteria included in the 

 ice diminishes. The greatest proportion of bacteria has 

 been found to occur in the snow-ice, although, on the 

 whole, there seems to be no uniform distribution of the 

 bacteria in any one layer. Their number may vary 

 from less than one hundred to several thousand per 

 cubic centimeter. As the ice melts, the number of bac- 

 teria in the ice-water begins to increase, attaining at 

 times, very considerable proportions. One instance is 

 reported in which a piece of ice was melted and im- 

 mediately examined. The number of organisms per 

 cubic centimeter was 1,020, whereas, eleven days later 

 the ice-water was found to contain 220,000 bacteria. 



The partial destruction of the bacteria by freezing, 

 and their subsequent multiplication in the ice-water, 

 may have a direct bearing on the typhoid question, 

 since it has been observed that not all of the bacteria 

 are affected to the same extent by freezing. It is quite 

 possible that the disease germs may survive in much 

 greater proportion than the harmless bacteria, and may 

 subsequently multiply as the ice melts. Typhoid germs 

 do not appear to suffer from the competition of other 

 bacteria at lower temperatures so much as they suffer 

 from it at higher temperatures. Savage states that "At 

 the temperature of the ice-chest, the typhoid germ may 

 grow in the by-products of other germs, which, at higher 

 temperatures, are quickly fatal to it." 



