490 EFFECTS OF INCREASE OF PRESSURE. [Book ii. 



£ 309. The Effects of Increase of Atmospheric Pressure. 

 These are in many ways remarkable. Up to a pressure of sev- 

 eral atmospheres of air, the only symptoms which present them- 

 selves are those somewhat resembling narcotic poisoning. The 

 animal becomes sleepy and stupid, the result probably not so 

 much of respiratory changes, as of the effects of the increased 

 pressure on the whole organism to which we have just alluded. 

 At a pressure however of 15 atmospheres of air, or what amounts 

 to the same thing, of 3 atmospheres of oxygen, and upwards, a 

 very remarkable phenomenon presents itself. The animals die 

 of asphyxia and convulsions, exactly in the same way as when 

 oxygen is deficient. Corresponding with this it is found that 

 the production of carbonic acid is diminished. That is to say, 

 when the pressure of the oxygen is increased beyond a certain 

 limit, the oxidations of the body are diminished, and with a still 

 further increase of the oxygen are arrested altogether. The 

 oxidation of phosphorus is perhaps analogous ; at a high pres- 

 sure of oxygen phosphorus will not burn. Not only animals 

 but plants, bacteria, and organized ferments, are similarly killed 

 by a too great pressure of oxygen. 



