Contributions from the Biological Laboratory of the U. S. Fish Commission, 
Woods Hole, Massachusetts. 
THE GAS IN THE SWIM-BLADDER OF FISHES. 
By R. W. TOWER, 
Associate Professor of Chemical Physiology, Brown University. 
The function of the swim-bladder of fishes has attracted the attention of scien- 
tists for many centuries. The role that this structure plays in the life of the animal 
has been interpreted 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 swirn- 
bladder. Consequently any additional data concerning this organ is 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 sound is produced.” 
The bladder was thus considered a sound-producing organ, and it is probable that he 
arrived at this result by his own investigations. 
Borelli* (1680) attributed to the air-bladder an 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 pre- 
vailed, to a greater or less degree, from the time of Borelli to the present. To my 
knowledge, 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 
directly contradict this belief. Delaroche f (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 sur- 
rounding medium and thus be able to remain at an} 7 desired depth (and not to rise 
and 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 consider the swim-bladder an organ of respiration. 
♦Borelli, De Motu Animalium, 1680. 
f Delaroche, F., Annales da Mus. d’Hist. Nat., tome xiv. 
