GAS DISEASE IN FISHES. 371 
only after it has flowed a considerable distance from its source in a 
shallow open stream. Failing this it may be carried through a circuit 
of a long and wide trough, to pass finally through perforated deaerat- 
ing pans. In general a complete exposure to the atmosphere is neces- 
sary and the means for accomplishing this will vary with the conditions 
of each individual case. The deficit of oxygen is more readily supplied 
than the excess of nitrogen removed. The water eagerly takes up the 
oxygen it lacks, but the last traces of excess of nitrogen come away 
with difficulty. 
When water rises as springs or wells in the bottom of the fish ponds 
themselves, it is still more difficult of correction, and quite impossi- 
ble unless the head is strong enough to lift the water above the level 
of the surface of the pond, and so permit the adoption of the above 
measures. 
It isa fact of significance and importance, to be considered from 
the standpoint of fish culture, that spring waters may vary consider- 
ably from time to time in the amount of dissolved air they contain. 
An instance of this, recently observed, concerned the oxygen alone, a 
marked deficiency being followed after several days and subsequent to 
a heavy rain, by a fairly abundant supply. It is inferred that nitro- 
gen variations may likewise occur, and presumably changes in the 
solids in solution. Weather and seasonal conditions probably are con- 
tributing causes of this variability, but not many observations have 
been made and little is known beyond the fact, which makes it neces- 
sary not to place entire reliance on one examination of a given water. 
In three instances of gas disease at government fish-cultural stations 
the excess of air has been actually determined by analysis. In others 
similar symptoms make a presumption of a similar cause. Meager 
information of other cases of disease or mortality among fishes with 
gas symptoms indicate with more or less probability the presence of 
supersaturation. A spring at an abandoned private trout cultural 
establishment in Vermont was found to be constantly giving up large 
bubbles of air (Table I, page 372, sample 5). Trout culture was not 
successful] in this water, and the former superintendent gave a history 
of bulging eyes. Analyses were not made, but it seems extremely 
probable that this water was supersaturated. 
In 1902, at the exhibit of the United States Fish Commission at the 
Charleston Exposition, a sudden and severe loss occurred among the 
marine fishes of the aquaria. The water precipitated quantities of 
gas, and the fishes were described as showing external bubbles and 
blisters of gas. The water supply was obtained by pumps with a long 
suction. The presumption is strong that the mortality was from 
excess of air, and that its sudden disappearance was caused by a change 
in the suction pipe, which, though unwittingly, corrected undetected 
leaks. The trouble was not explainable on other grounds than these. 
