on the Alr-lladder of Fishes. S99 



Delaroche confirms in general the experiments of M. Biot; 

 adding, that besides the varions decrees of depth at which 

 fishes hve, there are other causes whieh concur to vary the 

 proportions of the gases in their air-bladders. I'hus, of 

 two fishes caught on the same spot, one has given 50*0 and 

 the other scarcely 40 of oxygen. M. Delaroche also rec- 

 tifies the idea that M. Biot had civen of the eruption of 

 the bladder fruin ihe moulh, in fishes drawn up suddenly 

 ironi great depths, when he says that a rupture of the blad- 

 der then takes place, and that it is the air which forces up 

 the stoniaci) to the mouth. As to the source of this air, 

 -fuir authoF- (like Needham, Perrault, Monro. Koehlreuter, 

 Duvernoy and Cuvier,) thinks it is produced in the interior 

 oi' the bladder by a secretion of an unknown nature, of 

 which tl)e red bodies seem to be the organs in such fishes 

 as have these bodies. 



It is unnecessary to ask for a proof of this opinion in 

 fishes which have no exterior canal, for in them it is de^ 

 nionstrated by itself. We might also fairly extend it to 

 those which have a canal and red bodies, like the eel. 



But in those which want the red bodies, as we mnst 

 admit a new kind of exhalation, the analogy no longer 

 takes place completely ; and perhaps many persons would 

 be equally willing to have recourse to the aerial canal, in so 

 much as it always exists in this description of fishes. As 

 fishes of the same family frequently have the air-bladder, 

 and others want it, it is probable that its functions may be 

 supplied by different means. 



M. Delaroche, without considering that question as at all 

 decided, nevertheless supports the argument of analog}', 

 from the difliculty which any given gas would have in many 

 «5pecies, in penetrating into the bladder by the canal ; from 

 the still greater dlfiiculty which it would have of arriving 

 pure, particularly when it was requisite for it to pass through 

 <he substances coniaincd in the stomach ; and, lastlv, from 

 the difficulty of knowing, from whence, or by what mecha- 

 nism, the fish could procure it from nature, in order to intro- 

 /duce it into its bladder at great depths, where it is so fre- 

 quently and so long retained. 



The habit in wliich physiologists are of seein^r matters 

 of every kind come out of the blood by secretions, renders 

 ihem on the contrary very easy as to this kind of produc- 

 tion ; and in fact there is no real difficulty on the subject, 

 since azote and oxygen, which compose the air in the blad- 

 ^l.er, exist abundantly in the blood. 

 JBui it may be asked ; If the gas be c:!{haled or separated 



