^6 The Organs of Respiration 



found I to 5 per cent of CO^, i to 87 per cent of 0^, and the 

 remriindcr nitrogen. The most remarkable fact discovered 

 about this mixture Avas that it frequently consisted almost 

 entirely of oxygen, the per cent of oxygen increasing with the 

 depth of the water inhabited by the fish. The reasons for this 

 phenomenon have never been satisfactorily explained. 



"In 1820 Weber described a series of paired ossicles Avhich 

 he erroneously called stapes, malleus, and incus, and which con- 

 nected the airdDladder in certain fishes with a part of the ear — 

 the atrium sinus imparls. Weber considered the swim-bladder 

 to lie an organ by which sounds strikmg 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 centur3^ but re- 

 cently much has been written both for and against this theory. 

 Whatever the \'irtues 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 fislics. 



"Twenty years later Johannes iluUer described, in certain 

 Siluroid fishes, a mechanism, the so-called ' elastic-spring ' ap- 

 paratus, attached to the anterior portion of the air-bladder, 

 which ser\-ed to aid the fish in rising and sinking in the water 

 according as the muscles of this apparatus were relaxed or con- 

 tracted to a greater or lesser degree. This interpretation of the 

 function of the ' elastic-spring ' mechanism was shown by 

 Sorensen to be untenable. Miiller 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 gias in the air-bladder as the result of active secretion. In 

 Malaptentriis (Torpedo eleciricits) he stated that it is a sound- 

 producing organ. 



"Hasse, m 1873, published the results of his investigations 

 on the functions of the ossicles of AYeber, statmg that their 

 action Avas that of a manometer, accjuainting the animal with 

 the degree nf pressure that is exerted by the gases in the air- 

 bladder agamst its walls. This pressure necessarily varies with 

 the dhTerent depths of water which the fish occupies. Hasse 



