Miscellaneous. 263 



Of three Congers, taken under identical conditions, one killed at 

 once gave 30 per cent, of oxygen. Another was subjected to the 

 action of the air-pump until the column of mercury descended to 

 20 centimetres (= 8 inches), and then placed in a basin of sea-water ; 

 in two days it gave 62 per cent, of oxygen. The third was subjected 

 to the air-pum.p at a pressure of 9 centimetres (=3*6 inches) on 

 two consecutive days, then placed in the basin of sea-water, and 

 killed twenty-four hours afterwards ; the air in its swimming-bladder 

 gave 87 per cent, of oxygen. 



These examples suffice to prove that, in Physostomous fishes placed 

 where they cannot obtain air from the atmosphere, the swimming- 

 bladder is soon refilled with new air remarkably rich in oxygen, and, 

 further, that this is the case even in species which do not possess the 

 vascular organs known as the red bodies. 



In the case of fishes with a completely closed swimming-bladder, 

 the author punctured the bladder by means of a fine trocar, and 

 collected a portion of its air under water. The thickness of the 

 tissues penetrated prevents the access of water to the air-bladder 

 through the very narrow aperture made by the trocar, which closes 

 as the instrument is withdrawn. 



Four Perch, taken under the same circumstances, were punctured 

 under water. Their air contained from 19 to 25 per cent, of oxygen. 

 When killed, ten days afterwards, the amount of oxygen was from 

 40 to 65 per cent. 



Two Gilt-heads {Sparus auratus) furnished, when punctured, an 

 air containing 16 to 17 per cent, of oxygen. "When killed, two days 

 afterwards, they gave 58 and 59 per cent. 



A Wrasse {Labrus variegatus) gave on the first puncture 1 9 per 

 cent,, and twenty-four hours afterwards 57 per cent, of oxygen. 

 Another Wrasse gave 18 and 85 per cent. 



As the swimming-bladder cannot be completely emptied by the 

 above processes, and the remainder of the air, which is very rich in 

 nitrogen, is mixed with that which is finally obtained from the fish, 

 it would appear that, in some cases at least, pure oxygen must make 

 its appearance in the swimming-bladder. 



In a previous communication the author stated that asphyxia is 

 the cause of diminution in the proportion of oxygen in the swimming- 

 bladder, and also that this proportion diminishes by degrees, and 

 only reaches zero in the last moments of the life of the fish. If the 

 complete disappearance of the oxygen be desired, the fish must be 

 asphyxiated, in a larger quantity of water in proportion as he is more 

 vigorous and contains air rich in oxygen in his swimming-bladder. 

 Those fishes in which the swimming-bladder possesses no red bodies, 

 present a comparatively slight diminution of oxygen when asphyxiated. 

 Carbonic acid exists in the air of the swimming-bladder ; but in 

 most species examined by the author it was rarely present in a 

 larger proportion than 2 or 3 per cent. Asphyxiated fishes do not 

 exhibit an increase of this gas proportional to the diminution of 

 oxygen. 



