GAS DISEASE IN FISHES. 349 



freezing point fishes show within some three minutes after their 

 introduction a reaction consisting of extremel>' minute and very 

 close-set gas bubbles. Within about ten minutes the bubbles visibly 

 increase in size and become m\ich more conspicuous, enveloping the 

 fieh completel}^, body and fins, in a delicate, shimmering la^er of 

 silver}" white. It is evident that the bubbles do not emanate from 

 the fish itself, although thej" appear to; almost any surface within 

 the water, as that of rocks and the sides of the aquarium, exhibits 

 the same phenomenon. Neither are they free bubbles afloat in the 

 water which happen to attach themselves by contact to the bodies of 

 fishes — though this ma}' occur and simulate, in any water, the appear- 

 ance under discussion — because the same occurrence takes place after 

 all free bubbles have been allowed to rise and escape and fish are 

 immersed in perfectly clear and quiet water. The gas is a precipitate 

 from the water itself, in which it must hav'e been in solution. At 

 first, while the bubbles arc very small, they are quite closely adherent 

 and the fish may execute rapid movements without dislodging them. 

 As they grow larger they detach themselves readily and rise to dissi- 

 pate at the surface. A sudden movement will release a cloud of 

 hundreds or thousands of bubbles. A few seconds' removal of the 

 fish from the water will completely dissipate all the bubbles, but after 

 its return to the water they are soon formed again in their usual 

 abundance. In fact, these bubbles are more or less a feature of all 

 the fishes as long as the latter remain in water of this quality. 



The gas in the tissues, which manifests itself in blebs of the greatest 

 diversity in size and location, does not appear immediately, but only 

 after several hours at the earliest. The blebs may arise at any point, 

 the favorite seats being the fins and the head (fig. l,pl. i). This lesion 

 consists merely of a local accumulation of gas in or beneath the skin, the 

 outer layer of which is often stretched to an attenunted thinness by the 

 expansive pressure. If theso-called " slime'' of the skin is abundant, 

 bubbles may form within it, in which case they are small and numerous. 

 The tautog has an abundance of this slime and presents a characteristic 

 picture after a reaction of several hours. The luibbles tend to buoy 

 the slime and tear it from the body; it is partly separated in long 

 streamers, which remain attached at one end while they float suspended 

 in the water, buoyed by the bubbles which cling to the surface and 

 are embedded within the substance. This fish takes on, after about 

 an hour, a strikingly ragged and tattered appearance, which is shown 

 by no other species save the cunner. In fact, each species exhibits the 

 external gaseous lesions in a way more or less peculiar to itself. The 

 tomcod is especially prone to develop a few extraordinarily large 

 vesicles of gas in its fin membrane. The buoyant action of these is 

 often considerable, and when they are present in the caudal or last dor- 

 sals they tilt the fish out of position and require a constant effort to 



