36 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Now, as may be seen by referring to tlie table of the depths from which the fish 
under consideration were taken, a reduction of pressure must take place when fish 
are confined in shallow aquaria. Their tissues relax under the reduction, and any 
gas present must expand. Since, according to the law of the expansion of gases, a 
volume of gas occupies just twice the space at the surface that it does at 54 fathoms, 
a fish drawn from 300 fathoms to the surface must suffer an expansion of its contained 
gases to over 54 times their original volume. 
Gas is present in all fish, in the alimentary tract, in the air bladder, and in the 
blood and other fluids of the body. As this gas expands and seeks an outlet the 
tissues are loosened and torn apart; the intestine and air bladder are greatly distended 
and perhaps ruptured, the circulation of the blood is impeded or stopped, and 
vesicles of gas form in various parts of the body. 
These phenomena have been noticed for a long time in fish taken from great 
depths. Such fish are usually dead when they reach the surface, their eyes are pro- 
truded, their air bladder is ruptured, their intestines are everted from mouth or anus, 
and their scales are often lifted from the skin. The greater the depth from which 
they come the more pronounced are the changes. So great is the pressure to which 
some of the deep-sea fish are subjected ( Melampliaes beanii from 2,940 fathoms sustains 
a pressure of 3.9 tons per square inch), that the structure of the bones, connective 
tissues, and muscles is peculiarly modified. Even in fish taken from 15 or 20 fathoms 
one may note the protrusion of the eyes, the eversion of the intestine, and the noise 
of the expanding gas working through the tissues. 
We are thus led to the conclusion that the “gas bubble disease” is caused by a 
reduction of pressure. Naturally, the disease has never been noticed except in the 
aquaria; normally shallow- water fish are never affected, and the greater the normal 
depth of a fish the more severely is it affected. Occasionally certain deep-water fish 
voluntarily seek the surface, but it is only when they can not return to deeper water 
that the changes brought about by the expansion of gases become evident. 
It is interesting to compare these changes in fish with those observed in higher 
animals when subjected to alterations of pressure. Animals at the surface of the 
earth are subjected to an atmospheric pressure of about 14.7 pounds per square inch. 
When this pressure is diminished or increased, physiological changes result. Moun- 
tain climbers, at an elevation of 2 miles, suffer from increased rapidity of respiration, 
quickened pulse, painful, throbbing headache, flow of blood from the nose, eyes, and 
mouth, nausea, and vomiting. On the other hand, when the pressure is increased to 
from 50 to GO pounds per square inch, as in caissons, workmen experience an annoy- 
ing sensation about the tympanum, an irritation of the skin called the “puces,” an 
alteration of the voice, deep, slow, and easy respiration, active digestion, an absence 
of thirst, and an increased secretion of saliva and urine. Return to normal pressure 
has the same effect as going into rarefied air. The “puces” is replaced by a chill, 
respiration becomes difficult, the pulse is rapid and hard, there are pains in thejoints and 
muscles, and persistent cramps, paralysis, and coma are frequent; death may result 
in a few minutes. In such cases autopsies have shown congestion of the viscera, 
emphysematous spots on the lungs, and other indications that the blood contained 
bubbles of gas.* 
*1 am indebted to Mr. Frederick T. Lewis for calling my attention to tliese facts. See “The 
physiological effects of compressed air,” in the Boston Medical and Surgical Journal, October 6, 1898. 
