GAS DISEASE IN FISHES. 3849 
freezing point fishes show within some three minutes after their 
introduction a reaction consisting of extremely minute and very 
close-set gas bubbles. Within about ten minutes the bubbles visibly 
increase in size and become much more conspicuous, enveloping the 
fish completely, body and fins, in a delicate, sbimmering layer of 
silvery white. It is evident that the bubbles do not emanate from 
the fish itself, although they 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 may 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 have been in solution. At 
first, while the bubbles are 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. 1, pl. 1). 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 attenuated thinness by the 
expansive pressure. If the so-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 bubbles 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 
