GAS DISEASE IN FISHES. 375 
5. The form of the disease caused by the reduction of pressure alone 
occurs only experimentally, or possibly in the case of some deep-sea 
fishes brought to the surface. 
6. The form of the disease caused by an excess of dissolved air alone 
is the normal one. Nitrogen excess is more important than oxygen 
excess and ean singly cause the disease process. 
7. An excess of about 2 c. c. of nitrogen per liter of water is sufli- 
cient to cause symptoms. An excess of about 6c. ¢. per liter, accom- 
panied by an excess of about 2 c. c. of oxygen, experimentally 
produced, has been observed in sea water, and kills most adult fishes 
in a few hours. 
8. A certain increase of pressure will prevent the gas disease where 
otherwise it would oecur, and may cure affected fishes. It acts by 
changing the saturation point so that the excess of air no longer exists. 
9, The supersaturated water may be corrected and become harmless 
by deaeration. This occurs spontaneously upon standing or may be 
more quickly accomplished by subdividing the water mechanically to 
offer a great area of exposure to the atmosphere. This process cor- 
rects either an excess or a deficiency of air. The water of shallow 
brooks arising in supersaturated springs or wells is soon corrected by 
the natural flow. 
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