1093 
The stimuli awakened by a modified pressure are certainly per- 
ceived via other channels besides that suggested by BaGLiont. 
Il. The air in the air-bladder. 
Since Priester we have known already that the gases, found in the 
air-bladder, are the same as those of the air. The proportion between 
oxygen, nitrogen, and carbonic acid varies, however, to a considerable 
extent. As a rule fishes living in deep water have a high percentage 
of oxygen; sometimes it rises to + 90°/,. 
It was established experimentally that the fish is able to gather 
gases in the interior of its bladder, for example when the gases, 
present in the first instance, are removed by means of a trocar or 
air-pump (physostomi). 
Moreau proved that the newly-formed gas is oxygen, at least that 
after the gas-regeneration the percentage of oxygen is considerably 
higher than before. 
The fish can regulate the gas-pressure in the air-bladder in accord- 
ance with the outward pressure to which the fish is subjected. 
Deep-sea fisbes have extremely high tensions in the air-bladder whilst 
in animals kept under an artificially increased or decreased pressure, 
an increase or a decrease in the tension of the air-bladder can be 
demonstrated. 
This gas-production cannot be a simple osmotic phenomenon, 
especially on account of the enormous tension met with in deep-sea 
fishes; it is a secretion. It is easiest to prove the secretion of oxygen ; 
according to Hürner’s investigations, however, we must also assume 
nitrogen-secretion. 
This secretion has especially drawn the attention of Bonr in con- 
nection with his researches and hypotheses on the gas-changes in 
the lungs, which, as we know, are likewise reduced by him to a 
secretory phenomenon. 
Bonr determined which nerves influence the secretion. Moreau 
had suggested already that cutting the sympathie fibres occasioned 
an increase in the oxygen-percentage. These nerves would, therefore, 
impede the oxygen-secretion. BoHr cut on both sides the vagus- 
branches innerving air-bladder and intestines and found that the 
secretion ceased entirely. 
By a series of experiments I tried to fill up to some extent some 
gaps in our knowledge relating to the secretion-phenomena de- 
scribed above. 
Fishes kept under a continually variable pressure adapt themselves 
72* 
