American Fisheries tiociety. 195 



amount of which would never exceed that which the coldest 

 water would ahsorb at the highest atmospheric pressure. The 

 depths of such waters are of course under an increased pressure, 

 which is proportional to the depth, and if air were present at 

 these depths the water would absorb an excess of it. By excess 

 is meant always that amount over and above what the water 

 could hold if it were at the surface and therefore under atmos- 

 pheric pressure only. 



Under natural conditions water will seldom acquire an excess 

 of air. But under certain artificial conditions the water and air 

 may be brought together under a greatly increased pressure more 

 than the atmospheric. In this case an excess of air will be 

 forced into the water. The water will become supersaturated. 

 This is what occurred at Woods Hole. The arrangement of the 

 water supply you can yourselves examine. A steam pump takes 

 up water from the harbor through a long suction pipe and forces 

 it up into two reservoir tanks. It flows thence by gravity to the 

 hatchery and aquaria. The height of these tanks is about 

 eighteen feet and the pressure at the pump is about eight pounds 

 made by this eighteen foot column of water. The pump was 

 found to be forcing, not water alone, but water containing many 

 bubbles of air which entered presumably through a leak or leaks 

 in the suction pipe. This air does not dissolve in the water to 

 any great extent until it passes the pump, whereupon it enters 

 the region of increased pressure and commences to pass into solu- 

 tion. We may assume that the sea water when it enters the suc- 

 tion pipe contains all the air it will hold at the temperature 

 which prevails and at the existing atmospheric pressure. It may 

 fall somewhat short of this, but the point is immaterial. At any 

 rate, it reaches the storage tanks containing too much air — 

 invisibly present in solution. It is now exposed to the air and 

 some of the excess may pass off, but as water is constantly pass- 

 ing through the tanks there is no time for this process to accomp- 

 lish much. It reaches the aquaria and hatchery boxes with it-s 

 considerable excess of air, and it causes upon any fishes present 

 the svmptoms already described and which finally end in death. 



The processes of release of the excess of air from solution, 

 and of its appearance within the circulation of the fishes are to 

 l)e considered. The pressure being removed, air begins to leav: 



