86 ILLINOIS STATE ACADEMY OF SCIENCE 



mecium, Ameba, and other protozoa were common in the 

 water and mud cultures. 



On February 22, four samples of ice and two of water 

 were collected and treated the same as before. Three cul- 

 tures of sterilized lake water and nutrient agar were 

 made at the same time and subjected to the same con- 

 ditions in order to determine if infection from the air 

 could account for any of the resulting forms. Observa- 

 tions on all these cultures were made February 27 and 

 March 4. In the ice cultures, Chlamydomonas and bac- 

 teria appeared. In the water cultures, Chlamydomonas, 

 Pleuromonas, Ameba, and other protozoa were common. 

 In the sterilized lake water culture used as an additional 

 check, no forms of life were present, indicating that the 

 probability of the origin of any of these forms from the 

 atmosphere was slight. 



On February 7, four cultures of Chlamydomonas, con- 

 taining also Paramecium, were frozen from twelve to 

 twenty-four hours and then thawed. The cultures were 

 kept isolated and were observed February 14. The on y 

 forms observed after thawing were Chlamydomonas and 

 bacteria. These organisms were present in all four cul- 

 tures. The Paramecium which were common before 

 freezing never appeared after freezing and thawing. 



In the eight samples of ice collected from Lake Decatur 

 at three different dates, bacteria and Chlamydomonas 

 seemed the only forms present. From the water just 

 under the ice, many different protozoa were obtained. 

 In all the cultures, except those of sterilized lake water, 

 bacteria were observed, but were not regarded as of much 

 significance as they easily withstand freezing and thaw- 

 ing. It seems that Chlamydomonas is the only form of 

 protozoa in Lake Decatur able to survive freezing and 

 thawing. 



