34 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
The following invertebrates showed signs of the disease: Squid, naked mollusks, 
scallops ( Pecten tenuicostata), hydroids ( Paryplia crocea). Squid egg-sacs and some of 
the green alga: also developed internal bubbles apparently of the same nature. 
Minnows (Fundulus heteroclitus and Cyprinodon variegatus) and skates ( Raja 
erinacea ) in no case were affected. 
In most fish the disease manifests itself first on the fins, but in the scup it attacks 
the socket of the eye and gradually forces the eyeball from the orbit (plate 12). In 
the adult puffer the dorsal fin is first attacked; in the young puffer the base of the 
tail. In the pipe-fish the bubbles appear about the snout and later spread to other 
parts of the body. In young winter flounders (about 1 centimeter long) the body 
cavity frequently contains a large bubble. 
The disease is not confined to the aquaria at Woods Hole. Mr. L. B. Spencer, 
who is in charge of the Battery Park Aquarium in (New York City, writes me that he 
has noticed it there for several years. 
Prom the appearance of the fish, from the rapid development of the disease in fish 
introduced into the aquaria, and from the nonappearance of the disease in fish outside 
of the aquaria, it at first seemed to me that the aquaria had become infected with some 
disease producing organism, that the organism was a “gas producer,” and that it 
spread rapidly through the tissues of the fish and produced the gas which collected as 
bubbles in various parts of the body. With this idea in mind the task of finding, 
isolating, and studying the organism was begun. 
All of the tissues of the fish were searched thoroughly for foreign organisms; 
hundreds of cultures were made on the ordinary and also on special media, such as 
fish-bouillon, fish-gelatin, and fish -agar. The cultures were kept warm, cold, and at 
the temperature of the water in the aquaria; cover-glass “ smears” were repeatedly 
examined; but all to no purpose. Not a sign of any pathogenic organism was found. 
The only pathological change noticed in the tissues was a remarkably emphysematous 
condition of epidermis, muscles, connecti ve tissue, fat, etc., in the neighborhood of the 
vesicles. I became convinced that the disease could not be attributed to the invasion 
of micro-organisms. 
Two phenomena suggested a new line of inquiry: (1) None of the small shallow- 
water fish developed bubbles; (2) the deep-sea fish when brought to the surface by 
line or dredge often show a protrusion of the eyes and an expansion of the tissues, 
comparable to the conditions under consideration. Could not the disease be the direct 
result of the reduction of pressure upon the tissues of the fish, a reduction which 
must occur when animals habituated to a life in deeper water are compelled to 
live in the shallow water of the aquaria? 
To answer this question the following experiment was made: Several young scup 
were placed in water in a flask; the air was then exhausted from above the water, 
thus reducing the pressure. As soon as the pressure was at all diminished, the fish 
immediately sought the bottom of the flask, heads down, and made every effort to 
seek deeper water and thus regain their normal pressure. By their continued struggles 
they soon became exhausted and came to the surface. The atmospheric pressure was 
then restored and they became quiet and swam about naturally. The reduction of 
pressure was repeated three or four times at intervals of 30 minutes. After the 
experiment the eyes of the fish showed well-developed bubbles. The experiment was 
repeated on the following day, with the same fish, with the result that the bubbles 
enlarged until the eyes began to protrude. 
