GAS DISEASE IN FISHES. 359 
water outside the hatchery for twenty-four days and nosymptoms of the 
disease appeared. At the end of this time, when placed in the super- 
saturated water of the aquaria, the same scup died quickly, with all 
the symptoms of gas disease. There is a considerable reduction of 
pressure brought about in bringing scup from their natural depths 
(2 to 20 fathoms) to the surface. The pressure at 54 fathoms is twice 
that at the surface. But the fish can accommodate themselves to this 
reduction. The increased volume of gas in the air bladder is dimin- 
ished through absorption by the blood, and the gills remove it by 
osmosis to the sea water. 
Experimentally, however, reduction of pressure below that of the 
atmosphere is sufficient to produce the disease. The experiments 
reported in the previous paper (Gorham, 1899), which have beeti 
repeated and extended, demonstrate this. They were carried on by 
placing fishes in sea water in a large jar from which the air could be 
exhausted by a pump, and the vacuum secured measured by a gauge. 
Fishes could be killed very quickly (forty-four minutes) by a rapid 
reduction of the pressure to about 20 inches of vacuum, or about 
one-third of an atmosphere. These fishes gave the symptoms of gas 
disease such as the presence of a gas bubble in the heart and gas in 
the other vessels. By a less reduction, or by a series of reductions 
with periods of rest between, it was possible to bring about the for- 
mation of the external lesions of the disease, such as pop-eve, blebs in 
the fins, etc. Similarly an increase of pressure, brought about by 
forcing air into this same jar or by subjecting fishes to the pressure of 
a considerable depth of water, will cure or prevent the disease. Symp- 
toms of the disease such as protruding eyes and blebs on the fins, which 
have been caused by placing fishes in supersaturated water, will disap- 
pear when the fishes are placed under these conditions of increased 
pressure. It should be said, however, that the presence or absence of 
an air bladder is probably important in determining the presence or 
absence of free gas within the blood vessels of fishes drawn from 
depths to the surface. There seems to be no reason why such fishes 
lacking an air bladder should show embolic gas or any free gas which 
was not free at the beginning of the change of depth. As far as the 
writers are aware, no observations have been made or are of record. 
While the saturation point of both water and blood at great depths is 
tremendously increased, deep waters do not have a greater air content 
than surface waters. They have, in fact, less of oxygen, and of nitrogen 
approximately the same as or less than surface waters, but never more. 
(Dittmar, 1884, p. 225.) This follows from the fact that the air in 
deep waters was taken up at the surface, and that the oxygen may 
be constantly diminished by oxidation processes while the nitrogen 
remains unchanged. The blood of deep-sea fishes without air bladders 
should never, therefore, contain more air than it can hold at the 
