GAS DISEASE IN FISHES. 359 



water outside the hatchery for-twenty-four days and no symptoms of the 

 disease appeared. At the end of this time, when phiced in the super- 

 saturated water of the aquaria, the same scup died quickl}-, with all 

 the S3'mptoms 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 5^ 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 been 

 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. 

 Eishes could be killed very quickly (fortj'-four minutes) l)v 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. B}" a less reduction, or b}' 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-ej-e, blebs in 

 the fins, etc. Similarly an increa.se 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 b}" placing fishes in supersaturated water, will disap- 

 pear when the fishes are placed under these conditions of increased 

 ;^ressure. 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 wh}" 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. Thev have, in fact, less of oxj'gen, and of nitrogen 

 approximate!}' the same as or less than surface waters, but never more. 

 (Dittu^r, ISS-i, p. 225.) This follows from the fact that the air in 

 deep waters was taken up at the surface, and that the ox^^gen may 

 be constant]}' 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 



