FISHES. 365 



cessantly engaged in making it flow to, and pass between, its branchiae, 

 by the motion of its jaws, and of its opercular and hyoidean appa- 

 ratuses, such as we have described them above. This process, respi- 

 ration, is as indispensably necessary to fishes as the respiration of air 

 to other animals ; they exhibit the same symptoms of distress when it is 

 stopped, and very rapidly perish. Still the action of the water on 

 the blood is far more feeble than that of air; it is not by itself, neither 

 is it by oxygen, which enters into its composition, that the water 

 acts ; it is not decomposed, and it is only the small quantity of air 

 that it keeps in solution and mixes with itself, which serves for the 

 respiration of these animals : if it be deprived of air by boiling, it 

 kills them instantly ; it is even necessary for some fishes to come up 

 to respire the air in its natural state, especially when the water in 

 which they live is exhausted of it. We have very conclusive expe- 

 riments on this head, and it is only necessary to remove certain fishes 

 from the surface of the water by means of a diaphragm of gauze to 

 asphyxiate them*. 



In this resjjiration, as in that of the higlier animals, the atmos- 

 pheric air, as well as the air contained in the water, loses its 

 oxygen(a). 



* Spallanzani has shown that fishes absorb oxygen and convert it into carbonic 

 acid. M. Silvestre has shown that they respire atmospheric air, or that which is 

 contained in water. M. M. De Humboldt and Provencal, applying to this question 

 the processes of a perfect chemistry, have obtained the results spoken of above. 

 Their memoir is inserted amongst those of the Society of Arcueil, vol. xi. p. 339, et 

 seq. and in the Zoolog. Observ. of M. De Humboldt, vol. xi. p. 294. 



!X^ foj In their character of cold blooded animals, the fishes have been sub- 

 jected to more extensive enquiries and experiments than any other of the cold- 

 blooded orders. Spallauzani, Sylvestre, Humboldt, Provencal, Priestley, Edwards, 

 and others, have made this class the object of their minutest attention. 



Priestley, who imagined that the principal use of the blood and lungs in man and 

 other mammalia, was to eject phlogiston (1) from the system, thought that it would 

 ■be interesting to find out if fishes gave any of this phlogiston to water. 



With this view he put two (a large perch and an eel) into a pail of water ; and 

 '»vhen they had been in it about twenty-four hours he nearly filled a large phial with 

 the water, and in it he agitated a small quantity of common air between six and 

 •seven minutes, and found that it was considerably injured by the operation ; for two 

 measures of this and one sixth, and by standing several days were never less than 

 two measures. But when he agitated an equal quantity of air in the same quantity 

 of the same water in which no fishes had been confined, and for the same space of 

 time, it was not injured in the slightest degree. It is evident, therefore, according 

 to Priestley, that phlogiston is discharged from fishes as well as from other animals ; 

 that this phlogiston afi'ects the water, and this water the air that is agitated in it ; 

 and in the same manner as the fishes themselves would have affected it, if it had 

 been possible for them to breathe it. Other experiments confirmed and extended 

 these conclusions. Having filled a phial with some water from the hot well at 

 Bristol, which he found to contain i.ir in a great state of purity, he put a few min- 

 nows and other small fishes into it, about two inches in length, and confined them 

 without any access of common air until they died. He then took equal quantities of 

 the foul and of fresh water, and expelled from both all the air they would yield, 

 Tliat from the water in which no fishes had been put, or the fresh, exceeded the 

 foul in the proportion of three to two ; and by the test of nitrous air, the former 



(l) Phlogiston was the name of a combustible principle supposed to exist in all 

 ■bodies, and that when burned, these bodies gave out the principle. But Lavoisier's 

 discovery of oxygen gas exploded phlogiston. 



