BULLETIN OF THE UNITED STATES FISH COMMISSION. 
126 
Biot * * * § (1807), Provencal and Humboldt f (1809), and others made chemical 
analyses of the gas in the swim -bladder and found 1 to 5 per cent of C0 2 , 1 to 87 
per cent of O.,, and the remainder nitrogen. The most remarkable fact discovered 
about this mixture was that it frequently consisted almost entirely of oxygen, the 
per cent of oxygen increasing with the depth of water inhabited by the fish. The 
reasons for this phenomenon have never been satisfactorily explained. 
In 1820 Weber I described a series of paired ossicles which he erroneously 
called stapes, malleus and incus, and which connected the air-bladder in certain fishes 
with a part of the ear — the atrium sinus imparis. Weber considered the swim- 
bladder to be an organ by which sounds striking the body from the outside are 
intensified, and these sounds are then transmitted to the ear by means of the ossicles. 
The entire apparatus would thus function as an organ of hearing. Weber’s views 
remained practically uncontested for half a century, but recently much has been 
written both for and against this theory. Whatever the vixtues of the case may be, 
there is certainly an inviting field for further physiological investigations regarding 
this subject, and more especially on the phenomena of hearing in fishes. 
Twenty years later Joh. Miiller § described, in certain Siluroid fishes, a mechanism, 
the so-called “elastic spring” apparatus, attached to the anterior portion of the air- 
bladder, which served to aid the fish in rising and sinking in the water according as 
the muscles of this apparatus were relaxed or contracted to a greater or smaller 
degree. This interpretation of the function of the “elastic spring” mechanism was 
shown by Sorensen || to be untenable. Muller also stated that in some fish, at least, 
there was an exchange of gas between blood and air-bladder — the latter having a 
respiratory function -and regarded the gas in the air-bladder as the result of active 
secretion. In Malapteritrus he stated that it is a sound-producing organ. 
Hasse, 1 in 1873, published the results of his investigations on the function of the 
ossicles of Weber, stating that their action was that of a manometer, acquainting the 
animal with the degree of pressure that is exerted by the gases in the air-bladder 
against its walls. This pressure necessarily varies with the different depths of water 
which the fish occupies. Hasse did not agree with Weber that the ear is affected by 
the movements of these ossicles. 
One year later Dufosse ** described in some fishes an air-bladder provided with 
extrinsic muscles by whose vibrations sound was produced, the sound being intensified 
by the air-bladder, which acted as a resonator. He also believed that certain species 
produced a noise by forcing the gas from the air-bladder through a pneumatic duct. 
At about the same time Moreau ff published his classical work on the functions 
of the air-bladder. He proved by ingenious experiments that many of the prevailing 
ideas about the action of the air-bladder were erroneous, and that this organ serves 
to equilibrate the body of the fish with the water at anv level. This is not accom- 
plished quickly, but only after sufficient time for the air in the bladder to become 
*Biot, M&moires de Phys. et de Chimie de la Soc. d’Areueil, tome i. 
f Provencal et Humboldt, M6moires de Phys. et de Chimie de la Soc. d’Arcueil, tome n. 
JE. H. Weber, De Aure et Auditi Animalium Aquatilium. 
§ Joh. Muller, Archiv f. Anat. u. Physiologie, 1842, pp. 307 et seq. 
| Wm. Sorensen, Journ. of Anatomy and Physiology, vol. 29, 1894-95. 
1) Discussion of Hasse’s theory by Sorensen, op. cit., p. 534. 
** Dufoss6, Annales d. Sci. Nat.,5 c ser., tomes 19 and 20, 1874. 
i f Moreau, MOmoires de Physiologie, vol. 15, p. 494 et seq. 
