352 REPGRI OF THE COMMISSIONER OF FISHERIES. 
air at the intake it inevitably acquired a supersaturation on its journey 
from the pump to the storage tanks, due to the presence of air and the 
increase of pressure. In the storage tanks there was but slight 
exposure to the atmosphere and from them the water reached the 
aquaria containing its excess of air. In the aquarium tanks the water 
gives some evidence of its unusual condition in the form of precipi- 
tated bubbles of gas which gather on all solid surfaces in contact with 
the water, and in a minute effervescence which is barely visible when 
its perfectly smooth, unbroken surface is carefully observed. The 
actual effect of the release of these bubbles is to diminish but inappre- 
ciably the degree of excess while the flow is continuous, for the con- 
stant inflow is bringing new supplies of the supersaturated water. 
Influence on respiration of jishes.—The gill apparatus of fishes, for 
the osmotic interchange of gases which keeps the blood purified, is 
presumably adjusted to water the gases of which were dissolved at 
atmospheric pressure. The gills of any fishes in this aquarium water 
are therefore subjected to an osmotic pressure higher than any to 
which they were habituated in nature. Osmosis is accelerated and 
the blood takes up unusual quantities of air. The goal toward which 
the process tends is the same degree of supersaturation on one side of 
the gill membrane as on the other. In other words, the osmotic press- 
ure on the two sides tends to equalize, and, inasmuch as blood and 
water have approximately the same saturation point, the blood stream 
tends to acquire the same excess of air as the water, or to become 
actually supersaturated with air. This is believed to be what actually 
takes place. The circulation becomes supersaturated. 
In cases where fishes are brought up from considerable depths and 
confined in this water, the great reduction of pressure acting on the 
gas in the air-bladder and tissues permits the expansion of this gas. 
There is an attempt on the part of the fish to remove this excess gas, 
first by absorption into the blood and second by osmosis through the 
gills. But the second part of the process is inhibited by the already 
high gas content of the water in which the fish are placed. Thus in 
these fishes the supersaturation of the blood is more readily brought 
about. 
The subsequent release of gas within the vessels is to be explained 
chiefly by temperature changes within the blood. While fishes are 
cold-blooded animals, their body temperature is not exactly uniform 
with that of the surrounding medium. The combustion involved in 
the life processes implies the evolution of heat, and this heat is appre- 
ciable and has been measured. The venous circulation shows the 
highest temperature, and in fishes of several common marine species 
has been found to be from 2° to 12° F. warmer than the surrounding 
water (J. H. Kidder, 1879). Between the gills and the systemic 
veins, then, the blood undergoes a greater or less elevation of temper- 
