The Organs of Respiration 97 



did not agree with Weber that the ear is affected by the move- 

 ments of these ossicles. 



" One year later Dufosse described in some fishes an air-blad- 

 der provided with extrinsic muscles by whose vibration 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 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 any level. 

 This is not accomplished quickly, but only after sufficient time 

 for the air in the bladder to become adjusted to the increase or 

 decrease in external pressure that has taken place. The fish, 

 therefore, makes no use of any muscles in regulating the volume 

 of its air-bladder. The animal can accommodate itself only 

 gradually to considerable changes in depth of water, but can 

 live equally comfortably at different depths, provided that the 

 change has been gradual enough. Moreau's experiments also 

 convinced him that the gas is actually secreted into the air- 

 bladder, and that there is a constant exchange of gas between 

 it and the blood. In these investigations he has also noticed 

 that section of the sympathetic-nerve fibres supplying the walls 

 of the air-bladder hastens the secreting of the gas into the 

 empty bladder. Since then Bohr has shown that section of the 

 vagus nerve causes the secretion to cease. Moreau noticed in 

 one fish (T rigid) having an air-bladder supplied with muscles 

 that the latter served to make the air-bladder produce sound. 



"Again, in 1885, the Weberian mechanism was brought to 

 our attention with a new function attributed to it by Sagemehl 

 who stated that this mechanism exists not for any auditory 

 purposes ,nor to tell the fish at what level of the water it is 

 swimming, but to indicate to the fish the variations in the atmos- 

 pheric pressure. Sorensen tersely contrasts the views of Hasse 

 and Sagemehl by saying that 'Hasse considers the air-bladder 

 with the Weberian mechanism as a manometer; Sagemehl re- 

 gards it as a barometer.' The theory of Sagemehl has, naturally 



