17 



where some fish * have as much as 0*92 of oxy- 

 gen in their air-bladder. 



The 1st of July, in 17° 42' latitude and 

 34° 2V longitude, we met with the wreck of a 

 vessel, of which we distinguished the mast co- 

 vered with floating sea-weed. This shipwreck 

 could not have taken place in a zone where 

 the sea is constantly calm. The wreck came 

 perhaps from the stormy seas of the north, and 

 might be driven back to the point where the 

 vessel had perished, carried on by that extraor- 

 dinary whirl which the waters of the Atlantic 

 undergo in the northern hemisphere. 



On the 3d and 4th, we crossed that part of the 

 ocean, where the charts indicate the bank -J- of 

 the Maal-stroom ; toward night we altered our 

 course to avoid this danger, the existence of 

 which is as doubtful as that of the isles Fon- 



Aria contenuta nella Vesica natatoria, Pavia, 1809. Having 

 employed eight months in experiments on the respiration of 

 fishes, Mr. Provenzal and myself observed, that the fishes 

 absorbed not only oxygen, but also azot, and that the quanti- 

 ty of this azot absorbed differs in individuals of the same spe- 

 cies. The oxygen inhaled was very far from being equalled 

 by the carbonic acid, which the fish exhale from the whole 

 surface of their body ; and these facts tend to prove, that the 

 proportion of oxygen and azot vary in the air-vessel, accord- 

 ing as the vital action of the gills and the skin is modified by 

 the greater or less pressure, which the fish undergoes at dif- 

 ferent depths. 



* Trigla cucullus. 

 + Borda, Voyage de la Flore, vol. ii, p. 314. 



