CONDITIONS OF EXISTENCE 



TABLE VI 

 Showing the Solubility and Distribution of Atmospheric Gases 



37 



The oxygen content of water varies from o cc. per liter to 25 cc. 

 in the presence of green algas on sunny days. The bottoms of lakes 

 and ponds where much putrescible matter occurs are usually 

 without oxygen. The hypolimnion of lakes with a thermocline 

 is in part without oxygen in summer. Probably free oxygen is 

 usually necessary to most organisms except anaerobic bacteria. 

 Most animals that have been studied in behavior experiments 

 select water with some oxygen. While some species of fishes such 

 as suckers, small mouthed black bass, and some cyprinids appear 

 to be affected by a considerable decrease from saturation at 

 ordinary temperatures, this appears to be the exception rather 

 than the rule. Increase to 25 cc. per liter under experimental 

 conditions does not appear to have any marked effect upon fishes 

 so far as life and death are concerned. Allee working on isopods 

 found that an increase in oxygen increases size, vigor, and amount 

 of positive response to current as well as efficiency of response to 

 current. His results have been confirmed by several students 

 who have repeated the experiments using different forms. 



Juday has shown that a long list of common protozoa, worms, 



