1094 
to it by an increased or decreased gas tension. The increase is 
‘effected by secretion; the physostomi, which possess a channel from 
the air-bladder to the esophagus, bring about a decrease by letting 
one or more gas-bubbles escape, the physoclisti, which lack this 
safety-valve, by a slow resorption of gases into the blood. 
The first question | wanted answered was the following: is it 
possible to bring about by means of an artificial decrease of the 
specific gravity of a physoclistus, the same reaction, in the form of 
gas-resorption from the bladder, as that caused by a decreased out- 
ward pressure? For this purpose the time was determined, necessary 
for perches to adapt themselves to a pressure-decrease of 25 centi- 
metres of mercury. It was found that within 18 hours they had 
adapted themselves to more than 15 centimetres. Now when by 
means of corks, fastened to their body, the 5. G. of perches was 
lessened, the same downward swimming-reactions were observed as 
those occurring at a decreased pressure. The gas-tension in the air- 
bladder decreased much more slowly. The condition reached in the 
former experiment within 24 hours manifested itself in the latter 
category only after about 5 > 24 hours. 
Another question that suggested itself was the following: If a fish 
whose bladder has been emptied, is by means of a cork brought 
into artificial equilibrium with the surrounding water, will the 
regeneration of gases no longer take place? 
This turns out still to be the case. To a carp the air-bladder of 
which has been sucked empty, a cork is fastened on the back, ofa 
size to keep the animal in equilibrium in the water. After some 
days it floats on the surface. The gases have been regenerated again 
to such an extent that the fish emits air-bubbles when the air pressure 
is reduced to less than */, atmosphere. It follows from this that the 
secretion, viewed by Morrav and others as a reaction on an increased 
pressure from outside, is independent of the specific gravity of the 
fish as a whole, but is probably governed by the degree of tension 
of the bladder. 
This tension is but slightly modified by a vertical movement of 
the fish in the experimental basin (40 centimetres deep), if we compare 
it with the tension-change in the air-bladder caused by the bladder 
being sucked empty. 
Probably the stimulus causing gas-regeneration finds indeed its 
origin in the nervous terminal apparatus described by DeINEKA. 
As regards the influence of the gas-secretion on the nervous system 
I may mention that the experiences of Bour, with reference to the 
Gadus callarias were confirmed by me in the case of Cyprinus carpio, 
