244 



EFFECT ON THE BLOOD GASES 



brate, into convulsions, which resemble those of acute asphyxia. 

 Lorrain Smith observed that a bird could be thrown into con- 

 vulsions by 3 atm. 2 after its blood had been 38 per cent, 

 saturated with CO. It is evidently the extra tension and not 

 the quantity of oxygen in the blood which excites. Animals 

 which have been briefly exposed to high oxygen pressures and 

 then rapidly decompressed exhibit reflex hyper-excitability and 

 tetanic convulsions. The spasms may increase in intensity till 

 the whole animal becomes rigidly extended and can be lifted by 

 one leg like a piece of wood. The animals can completely re- 

 cover from so grave a condition within twenty-four hours, and 

 this is so because the oxygen gas which bubbles off on rapid 

 decompression is rapidly absorbed by the blood and tissues. 



The difference is most striking between two rats, one decom- 

 pressed from air, and the other from oxygen, after five minutes' 

 exposure of each to 20 atm. The rat exposed to air dies after a 

 few convulsive movements, and is swollen out with gas. The heart, 

 the veins, the fat, the liver, &c., are full of gas bubbles (nitrogen). 

 The rat exposed to oxygen, on the other hand, is convulsed, and con- 

 tinues to be convulsed for many minutes if a string is tied round 

 its windpipe, for it lives on the bubbles of oxygen gas set free in its 

 blood. These bubbles are fairly numerous in the veins, but neither 

 block the circulation nor appear evident to the naked eye in the 

 fat and organs. The lungs of the oxygen rat are intensely 

 congested. 



EFFECT ON THE BLOOD GASES 



The analyses of the arterial blood gases of animals exposed to 

 compressed air show that the amounts of nitrogen simply ab- 

 sorbed increase with the pressure as required by Dalton's law 

 (Bert, Macleod, and Hill). Example : 



