360 REPORT OF THE COMMISSIONER OF FISHERIES. 
coldest surface water. As for pressure conditions, then, no such deep- 
sea fish should liberate air from its blood when brought to the surface. 
Since, however, its habitat may be water whose nitrogen was dissolved 
at a low temperature, and it may be brought up into comparatively 
warm surface water, there exist theoretical conditions in which this 
result would be possible. That it actually occurs is unlikely, but is 
a matter for observation. The air-bladder factor has not been 
thoroughly worked out in the present study and is an interesting field 
for further experiment. 
Although under these experimental conditions it is possible to pro- 
duce the gas disease by reduction of pressure alone, yet the conditions 
are quite different from those which obtain when fishes are brought to 
the surface from depths. Fishes are in the habit of coming to the 
surface for short periods under natural conditions. They can accom- 
modate themselves for short intervals, at least, to changes in pressure 
ranging from that at the surface to that of considerable depths, 
though the amount of gas to be eliminated when a fish with an air 
bladder comes to the surface is very large. When forcibly drawn up 
from considerable depths great changes take place, for the eyes bulge 
from the head and sometimes completely out of the sockets, the fish 
is often ‘‘ poke-blown,” the stomach and other viscera pushed into the 
cavity of the mouth, and the air bladder expanded or ruptured. The 
removal of pressure causes the free gas always present within the 
body to expand, and occasions displacement of tissues and organs. 
It is an interesting question whether such fishes have free gas within 
the blood vessels. 
When the pressure is reduced below that of the surface, and quite 
rapidly, we would expect that the fish’s powers of accommodation 
would be overstepped and they would not be able to take care of the 
surplus gas so quickly produced. No opportunity for adjustment is 
given. Still more when a fish is brought from a considerable depth 
and confined at the surface in water which is already supersaturated 
with gas, the gills would be unable to discharge the excess from the 
blood and the production of the gas disease would be hastened. 
On the other hand, that the supersaturation of the water alone with- 
out the reduction of pressure is sufficient to produce the disease, we 
have abundant evidence. Surface fishes like /wadulus, usually quite 
hardy, succumb to the effects of the supersaturated water. Fresh- 
water fishes, like the trout, which have never been subjected to any 
decrease of pressure, quickly show the effects of supersaturation. 
CONCLUSIONS. 
In the light of these facts it seems to follow theoretically that no 
matter how great the quantity of air dissolved in water no gas disease 
‘an appear, provided the pressure is high enough; and conversely, no 
matter how high the pressure the gas disease will appear, provided 
