352 REPOET OF THE COMMISSIONER OF FISHERIES. 



air at the intake it inevitably acquired a supevsaturation 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 fishes. — The gill apparatus of tishes, for 

 the osmotic interchange of gases which keeps the blood purifled, 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 vv^ere 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 flsh 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 b}^ 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 hody 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- 



