THE IMMUNITY OF THE SWIM-BLADDER 241 



about 24 hours, while 300 per cent. 2 produced inflammation in 

 5 hours. Our results confirm his. 



Lorrain Smith suggests that inflammation of the lungs may 

 be a cause of caisson disease as well as decompression gas embo- 

 lism. We do not find much in our experiments to confirm this 

 view. The highest pressure hitherto used in caissons is 4-45 atm., 

 and the men never work for shifts longer than a few hours. It 

 seems to require about 24 hours at +7 atm. ( = 168 per cent, 

 atm. 2 ) to produce marked symptoms of pulmonary congestion. 

 No pneumonia results at this pressure if the partial pressure of 

 oxygen is reduced by the addition of nitrogen. 



We observed no sign of lung trouble in a monkey which was 

 exposed on many days to 8 atm. for 4-5 hours at a time. 



THE IMMUNITY OF THE SWIM-BLADDER TO 

 OXYGEN-POISONING 



The epithelium of the swim-bladder of deep-sea fishes, an 

 organ analogous in its development to a lung, seems to be 

 immune to high pressures of oxygen. 



The swim-bladder is a long sac usually lying dorsal to the gut, 

 of which it is an outgrowth. It is present in most, but not all fishes. 

 In some cases there is a ductus pneumaticus communicating with 

 the gut. The function of the swim-bladder is to adjust the specific 

 gravity of the body at any depth to that of the water, so that the fish 

 remains suspended without muscular effort. When the fish descends 

 in the water the air in the bladder is compressed, the specific gravity 

 of its body increases and the volume decreases, so that it tends to 

 sink farther ; when it rises the converse holds true. 



Thus a fish, hooked in deep water and once well started on the 

 upward journey, floats irresistibly to the surface and arrives with 

 a bladder either burst or vastly distended and projecting from its 

 mouth. The fish is apparently made uncomfortable by alterations 

 in the volume of its bladder, and the discomfort causes it to stay at 

 its proper depth. The swim-bladder, placed as it is in the fore part 

 of the body, also helps to preserve the normal position of the body 

 the head higher than the tail. 



The following ingenious experiments demonstrate the function 

 of the swim-bladder. A piece of cork is tied on to the dorsal fin of a 

 gold-fish large enough to float it to the surface of a tall jar of water, 



Q 



