Sudden Changes in Pressure 853 



by means of a copper tube was put in communication with the large 

 metal receiver (Fig. 33) in which the pressure had been raised to 

 10 atmospheres, then the communication cock c was opened, and 

 the equilibrium of pressure suddenly established. The animal then 

 seemed to cower, to crouch, as if frightened; but after a few 

 minutes, regained all its liveliness. 



There is no reason for surprise at these negative results, because 

 we have seen that workmen in caissons and divers in suits are 

 subjected to sudden pressures of several atmospheres without feel- 

 ing other inconveniences than more or less keen pains in the ears, 

 which pains animals do not seem to feel, since in animals, no 

 doubt, the Eustachian tube opens more easily than ours. 



The effect of sudden increases of barometric pressure, almost 

 non-existent in air-breathing animals, is, on the contrary, very con- 

 siderable in fish provided with a swimming bladder. Whether 

 the bladder is closed or not, as soon as the pressure of the air 

 above the water in which the fish is swimming is increased a little, 

 the fish drops to the bottom of the vessel, from which the greatest 

 muscular efforts can raise it only for an instant. But after several 

 days during which the pressure has been maintained, it regains 

 complete freedom of action. That is because during this interval a 

 new secretion of oxygen has restored to its swimming bladder its 

 original volume and to its body its original density. All these facts, 

 which I have often witnessed, have been completely described and 

 explained by Dr. Armand Moreau. 



Subchapter II 



INFLUENCE OF SUDDEN DECREASE OF PRESSURE 

 BEGINNING WITH ONE ATMOSPHERE 



The study of this influence presents great difficulties without 

 being particularly interesting. As a matter of fact, for slight de- 

 compressions, no matter how suddenly they are produced, the result 

 is almost negligible in air-breathing animals; for great decompres- 

 sions, it is combined with that of anoxemia, beside which it is of 

 only slight importance. 



When a sudden drop to a half-atmosphere is made, the animals 

 tremble, leap, sometimes whirl, but soon recover, or at least show 

 only the symptoms of asphyxia due to the low oxygen content of 

 their blood. 



