Sudden Changes in Pressure 855 



sel in which it is swimming is placed under a bell containing a mix- 

 ture of oxygen and hydrogen unproportioned. 



June 9. The fish is killed. There is no hydrogen in the swimming 

 bladder. 



Fish with closed bladders, becoming lighter than the water when 

 decompression is made, come to the surface and die on account of 

 the bursting of the overinflated bladder. This fact has long been 

 well known to fishermen, who pierce the bladder with a pointed 

 piece of iron or wood, so that the entrails may not burst and soil the 

 fish. 



The same phenomenon (I mention this so as not to return to this 

 type of data again) may be observed in fish with closed bladders 

 kept for several days under increased pressure: 



Experiment CCCCXCVII. May 4. Sticklebacks in the glass cylin- 

 drical apparatus. Subjected to a pressure of 2 atmospheres, they sink 

 to the bottom immediately. 



May 10. Swim freely. Decompression made; come to the surface 

 immediately. When removed, they die. 



So these fish had formed in their bladders a sufficient quantity 

 of gas to regain freedom of movement, with their original density. 

 But the decompression was fatal to them. 



The closed air bladder is therefore very unsuitably called "swim- 

 ming" bladder, because it is harmful to the fish and compels it to 

 remain at a certain depth of water, under pain of bursting at the 

 surface or sinking indefinitely into the depths, if it passes the 

 narrow limits between which it is permitted to move vertically. 



I succeeded in getting a result similar to that of Experiment 

 CCCCXCVII with frogs rapidly decompressed from 5 to 6 atmos- 

 pheres to normal pressure. When the air of the lungs expanded 

 enormously, the tracheal opening closed; the stomach issued 

 through the mouth, the lungs burst, and the body was transformed 

 into a sort of overinflated balloon. All that is simple and to be 

 expected. 



But let us return to air-breathing animals. When very rapid 

 decompression is made, they too die almost at once. Can an im- 

 portant part in this death be attributed to the suddenness of the 

 decompression? That almost reverts to the question which we 

 have already asked. Is the purely mechanical or physical effect 

 of the decompression perceptible? The experiments reported in 

 the preceding chapters show that it is very slight at any rate, be- 

 cause an animal can, for example (Experiment CCLI), be brought 



