Life of the Waters 381 



water, but bacteria also suffer a ' ' freeze out, ' ' so that ice har- 

 vested from sewage-contaminated water may be fit for drink- 

 ing. Analyses made by the Massachusetts State Board of 

 Health and the North Dakota Public Health Laboratory have 

 shown that clear ice taken from polluted water may contain 

 as low as 1% of the number of bacteria present in the water. 

 This is not true in all cases however as there are many fac- 

 tors influencing the result. 



Small bodies of water may undergo other changes than 

 those due to cold and heat, freezing and thawing. Many 

 pools, formed in spring from rain or melting snow, and 

 swarming with life in the early months of summer, dry up 

 completely during late summer or early autumn, with re- 

 sultant destruction of the life which they contain, except 

 those forms which are able to survive long periods of drouth 

 with consequent extremes of heat and cold. 



But in spite of the destruction of life, which occurs in 

 these temporary ponds each year, every succeeding year they 

 are swarming with living things again as though nothing 

 had happened. "What has become of this life meanwhile, and 

 how is its cycle maintained in winter when Jack Frost seizes 

 the waters of the North in his icy grasp ? 



Some aquatic animals and plants can over-winter in their 

 ordinary condition, their rate of increase being merely slowed 

 down temporarily. Many fresh water copepods may be 

 found beneath the ice in winter oftentimes even carrying eggs, 

 and consequently actively reproducing. Fresh water beetles 

 and some other insects live over winter, and the same is true 

 of rotifers, molluscs and other fresh water forms of both 

 plants and animals. There is a case on record of a frog re- 

 viving even after being frozen in a solid block of ice. Sir 

 John Franklin records the revival of frogs and fish after 

 freezing, a specimen of carp recovering sufficiently to "leap 

 about with much vigor after it had been frozen thirty-six 

 hours." An Alaskan fish has been reported by one observer 

 to survive freezing for "weeks" and "when thawed out they 

 will be as lively as ever. The pieces (which have been 

 chopped out of a frozen mass with an axe) which are thrown 

 to the ravenous dogs are eagerly swallowed, the animal heat 

 of the dog's stomach thaws the fish out, whereupon its move- 

 ments cause the dog to vomit it up alive." A Jonah among 

 the fishes! 5 



On the other hand some algaa have been found living in 

 hot springs with a temperature of about 170F. and some 



'The writer would hesitate to accept this story without corroborative 

 evidence. It has been cited however by Eigenmann in Ward & Whip- 

 pie's "Fresh Water Biology." 



