FISH IN GENERAL. 91 



ence of the ambient liquid by means of an almost infinite 

 subdivision of vessels on the surface of the branchial leaves ; 

 that liquid is water passing incessantly through the branchiae 

 by means of the jaws, and the opercular and hyoidean appa- 

 ratus acting in concert, as in other animals it is performed 

 with air ; but the action of water upon the blood is much 

 less powerful than that of air. It is not by means of the 

 liquid, nor yet of the oxygen contained in it, but by the small 

 quantity of air mixed with and held in solution in the water, 

 that their respiration is carried on ; for if the air be expelled 

 by ebullition, they cannot live in it, and many species are 

 obliged to rise to the surface for the purpose of breathing 

 in the atmosphere, particularly when the quantity in the 

 water is exhausted. This is proved in several cases by 

 merely keeping fish below the surface under a net of gauze, 

 which is sufficient to suffocate them. 



As with other animals, in respiration, both atmospheric air 

 and that contained in water give off their oxygen. But the 

 absorption of oxygen is trifling, for it has been calculated 

 that a man consumes of it fifty thousand times more than will 

 be required by a tench. Fish perish when exposed out of 

 water, not so much for want of oxygen, as because their 

 branchiae become dry, and the blood cannot circulate in them 

 with sufficient freedom. Hence the species whose branchial 

 openings are small, as the eel, or those who possess a re- 

 ceptacle for water, like anabas and ophicephalus, remain 

 alive longer in the air, than those whose gills are very open, 

 like the herring, who expire at the instant they are drawn out 

 of the water. It is remarked, that many fresh water species 

 which are subject to be at times deprived of water, have 

 organs of respiration of peculiar structure, and often admit- 

 ting of air more highly oxygenated than is the case with 

 others, and thus have a greater tenacity of life. There are 



