The Organs of Respiration 95 



from. Prof essor Tower's paper on "The Gas in the Swim -bladder 

 of Fishes " : 



"The function of the swim-bladder of fishes has attracted 

 the attention of scientists for many centuries. The role that 

 this structure plays in the life of the animal has been inter- 

 preted in almost as many ways as there have been investigators, 

 and even now there is apparently much doubt as to the true 

 functions of the swim-bladder. Consequently any additional 

 data concerning this organ are of immediate scientific value. 



"Aristotle, writing about the noises made by fishes, states 

 that 'some produce it by rubbing the gill-arches . . . ; others 

 by means of the air-bladder. Each of these fishes contains air, 

 by rubbing and moving of which the noise is produced.' The 

 bladder is thus considered a sound -producing organ, and it is 

 probable that he arrived at this result by his own investiga- 

 tions. 



" Borelli (De Motu Animalium, 1680) attributed to the air- 

 bladder a hydrostatic function which enabled the fish to rise 

 and fall in the water by simply distending or compressing the 

 air-bladder. This hypothesis, which gives to the fish a volitional 

 control over the air-bladder it being able to compress or distend 

 the bladder at pleasure has prevailed, to a greater or less 

 degree, from the time of Borelli to the present. To my knowl- 

 edge, however, there are no investigations which warrant such 

 a theory, while, on the other hand, there are many facts, as 

 shown by Moreau's experiment, which distinctly contradict this 

 belief. Delaroche (Annales du Mus. d'Hist. Nat., tome XIV, 1807- 

 1809) decidedly opposed the ideas of Borelli, and yet advanced 

 an hypothesis similar to it in many respects. Like Borelli, he 

 said that the fish could compress or dilate the bladder by means 

 of certain muscles, but this was to enable the fish to keep the 

 same specific gravity as the surrounding medium, and thus be 

 able to remain at any desired depth (and not to rise or sink). 

 This was also disproved later by Moreau. Delaroche proved 

 that there existed a constant exchange between the air in the 

 air-bladder and the air in the blood, although he did not con- 

 sider the swim-bladder an organ of respiration. 



" Biot (1807), Provencal and Humboldt (1809), and others 

 made chemical analyses of the gas in the swim-bladder, and 



