AIR IN THE SWIMMING BLADDER OF FISHES. 551 



gas could be detected ; nor was there any sensible quantity of car- 

 bonic acid. The proportion of oxygen gas was very various, 

 being sometimes very minute, and sometimes constituting almost 

 the whole of the gas. The air bladders of those fish which live 

 near the surface contained least oxygen gas, and the bladders of 

 those which were brought up from a great depth contained the 

 most. The following table exhibits the proportion of oxygen in 

 100 parts of the air in the different fish examined : 



Names of the Fish. Prop, of Oxygen. Names of the Fish. Prop, of Oxygen. 



Mugil cephalus (Linn.) Quant, insen. Scisena nigra, female, . 0-27 



Ditto. . . Ditto. Ditto, male, . . 0-25 



Mursenophishelena(Zacep.) Very little. Labrus turdus (Linn.) female, 24 

 Sparus annularis(Zinn.) female, 009 Ditto, male, . . 0-28 



Ditto, male, . . O f 08 Sparus dentex (Linn.) female, 0'40 



Sparus sargus (Linn.) female, 0-09 Sphyraena spet, (Lacep.) 0-44 



Ditto, male, . . 0-20 Sparus argenteus, . .0-50 



Holocentrus marinus (Lacep.) 0-12 Sparus erythrinus, . . Much 



Labrus turdus (Linn.) . 0*16 Holocentrus gigas, . . 0'69 



Sparus melanurus (Linn.) 0-20 Gadus merluccius (Linn.) 0.79 



Labrus turdus (Far. Linn.) 0'24 Trygla lyra (Linn.) . 0-87 



The depth at which the fish in the preceding table are caught 

 increases gradually, as well as the proportion of oxygen, from 

 the beginning to the end of the table. The last-mentioned fish, 

 the Trygla lyra, is always caught at a very great depth. The ex- 

 periments of Laroche confirm the accuracy of this curious fact. 

 The mean result, furnished by all the fishes taken at a depth 

 greater than 150 feet, was 0*70 of oxygen ; while the mean re- 

 sult, furnished by the fish caught at less depths, was 0-29. This 

 superior purity is not owing to any superior purity in the air of the 

 water of the sea at great depths. The air obtained from sea 

 water, brought~up from a great depth, yielded 0*265 of oxygen, 

 while that from water taken at the surface was purer. 



It is very remarkable that the air in the bladder of fishes, 

 taken near the surface, should be almost pure azote. But this 

 holds also with respect to fresh water fish. Thus Biot found the 

 air in the air-bladder of a carp to contain 0-03 of oxygen, while 

 that of a tench contained 0-16 ; and Geoffrey and Vauquelin 

 found the air in the air-bladder of pikes, loaches, and perches, 

 to contain 0-05 of oxygen. Humboldt likewise found very lit- 

 tle oxygen in the air-bladder of the Gymnotus electricus. 



