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VICTOR E. SHELFORD AND W. C. ALLEE 



water and ascribed the results to the carbon dioxide though all 

 the gases were affected. Loeb in his experiments on Amphipods, 

 says that the water had an acidity equal to M/500, which is 

 about 44.8 cc. per liter. None of the others give carbon dioxide 

 determinations. The presence of fishes modifies the results of 

 bubbling. 



TABLE 3 



Showing the results of bubbling gas through jars of water containing fishes, the jars 

 being 50 cm. high, with an exposed surface area of about ^S sq. cm. and holding 

 about 2.2 liters. The gas was introduced at the bottom. The nitrogen was not 

 determined because of the small quantity of water. Average flow 50 cc. per min. 



d. The reduction of gas content and the addition of particular gases 



A laboratory water supply is usually supersaturated with gases 

 when it comes from a body of water exposed to the atmosphere. 

 It is often unsuitable for animals because of its low oxygen and 

 high nitrogen content when it comes from wells (Marsh '10). In 

 the first case the animals suffer ill effects from the excessive 

 amount of gas, while in the second they suffer from the deficiency 

 of oxygen. Either of these difficulties may be remedied by pass- 

 ing the water through a series of perforated vessels or allowing 

 it to flow in thin sheets over large rough surfaces (Marsh '10). 

 To reduce the gas content to a point below saturation, requires 

 either the use of a vacuum pump or boiling. In either case all 

 the gases are affected and it is often necessary to add certain 

 gases in order to obtain the desired conditions. The exhausting 



