Effect of Freezing 97 



such cisterns, and the large amount of filth that may 

 have accumulated in them. 



BACTERIA IN ICE 



Freezing temperatures destroy a large proportion 

 of the bacteria in the water. They cannot, however, 

 be depended upon to destroy all of the bacteria, and 

 thus render the water sterile. This has been repeatedly 

 demonstrated by various investigators. Careful studies 

 have been made in this connection with the typhoid 

 bacillus, the cholera germ, the anthrax bacillus, and a 

 number of non-pathogenic organisms. It has been proved 

 that ice may become a source of infection and disease. 

 The process of freezing is often, in itself, insufficient 

 for the complete destruction of all the bacteria present 

 in the water. 



Under certain conditions, the longevity of the typhoid 

 germs and other bacteria may be considerably reduced. 

 This is particularly so when the process of freezing is 

 not continuous, but consists of alternate periods of freez- 

 ing and thawing. 



Such intermittent freezing may lead to the destruc- 

 tion of the typhoid, cholera, and other organisms within 

 a few days; whereas, spore-producing species, like the 

 anthrax bacillus, are not thus destroyed, owing to the 

 great resistance of the spores. Everything considered, 

 then, ice made from polluted water must be regarded 

 with suspicion. Artificial ice, on the other hand, when 

 made from distilled water, is almost free from bacteria, 

 and may be used safely in the household. Artificial 

 ice made from river-, well-, or spring-water contains a 



