FISHES. 367 



All this oxygen does not return under the form of carbonic acid : 

 there always remains a little in the body of the fish, which likewise 



1st Experiment. He expelled, by long boiling, the atmospheric air from 64 

 cubic inches of sea-water : he then excluded it from the air by means of mercury. 

 Having then introduced a small mullet, it was instantly convulsed, and died in a few 

 minutes. 



2d Experiment. A quantity of water was freed, by boiling, of its atmospheric 

 air : two receivers, each of the capacity of 36 cubic inches, were filled with this 

 water : into one of these two cubic inches of nitrogen were introduced, into the other 

 two of phos-oxygen. By long and constant agitation the gasses were dissolved by 

 the water, which was excluded from the contact of air by mercury. Into each of 

 the receivers two minnows were introduced. Those in the water holding nitrogen 

 in solution died in about four minutes, those in the water holding phos-oxygen, in 

 solution appeared totally uninjured, and when examined, after some hours, were still 

 alive and healthy. 



3d Experiment. The same receivers used in the last experiment were filled with 

 distilled water freed from atmospheric air by a second boiling. Into each of these 

 three cubic inches of phos-oxygen were introduced. The receivers were then 

 agitated for some tinie^ till the water in each of them had dissolved an equal 

 quantity of gas ; they were then inverted in a trough of mercury, so as to exclude 

 atmospheric air from them. Four minnows were then conveyed into one of them 

 through mercury. The receivers were now suffered to remain untouched for six 

 hours, when they were examined. The minnows were alive, and no gas remained 

 in the top of the receiver in which they had respired. The gas in the top of the 

 other receiver remained nearly the same as at the commencement of the experiment. 

 A quantity of lime-water was poured into each of these receivers ; in that in which 

 the fishes had existed there was a very perceptible cloudiness, occasioned, as Davy 

 supposed, by the formation of carbonat of lime ; in the other there was no percep- 

 tible change. 



From these experiments Davy concludes, that the venous blood in the gills of 

 fishes is phos-oxydated by the phos-oxygen held in solution by water ; and that car- 

 bonic acid, and probably water, are given out as excrementitious by the venous 

 blood in their gills. With respect to the decomposition of water by fishes in 

 respiration, as there is no evidence of hydrogen being formed, there can be no reason 

 for the supposition. 



But the most interesting of the experiments made on fishes, were those of Dr. 

 Edwards, in Paris, whose work " Influences des agens physiques," is referred to in a 

 note by the author. 



Dr. Edwards, during a series of experiments, the philosophical results of which 

 have not been exceeded since the days of Spallanzani, has proved that fishes are 

 affected precisely in the same way as reptiles by the privation of air. He also proved 

 that the former like the latter, could not bear an increase of temperature. The only 

 difference between the two orders of animals in this respect is, that the fishes are 

 influenced by this privation according to their size. The younger the fish and the 

 smaller, the less capable is it of bearing an elevation of temperature. After varying 

 in his experiments, the temperature and the quantities of water with which air was 

 mixed, he found from the results, that the following laws were established. 



1st. That the duration of life goes on increasing with an increase of the quantity of 

 aerated water, the temperature remaining the same. 



2nd. That the same result takes place when the quantity of water remaining the 

 same, we lower the temperature. 



3rd. That the duration of life remains the same, when, within certain limits, we 

 increase or diminish, at the same time, both the temperature and the quantity of 

 aerated water. 



It was ascertained, previously to the time of Dr. Edwards, that if a fish be placed 

 in a small given quantity of aerated water, the water absorbs the air in contact with 

 its surface, a fact from which this inference is readily deduced that the life fcf an 

 animal in a limited quantity of water will be protracted the longer, the more copiously 

 the water absorbs air to compensate for what it supplies to the animal. Now, Dr. 



