RESPIRATION 357 



the American diver referred to above was exposed for three 

 hours) one of the animals died from lung inflammation in 7 hours. 



The higher the oxygen pressure the more rapidly was the fatal 

 inflammation produced. The lowest oxygen pressure at which fatal 

 pneumonia was observed was 73 per cent of an atmosphere, after 

 4 days' exposure. At 40 per cent no ill effects were observed. It is 

 evident from these observations that when oxygen is used con- 

 tinuously for therapeutic purposes the percentage ought not to be 

 increased more than is really necessary. A lung that is already 

 inflamed may be extra sensitive to an unusually high oxygen 

 pressure. At an oxygen pressure corresponding to 57 fathoms of 

 water we found that out of seven goats one died in three hours 

 from pneumonia, while the others were also affected, but re- 

 covered on decompression. At an oxygen pressure corresponding 

 to 40 fathoms we could not detect in ourselves any subjective 

 symptoms during short exposures ; but quite probably such symp- 

 toms might appear after longer exposure, and the behavior, 

 described above, of the experienced American diver seems sug- 

 gestive of this. 



Although oxygen at high pressure acts generally as a poison, 

 yet as shown in Chapter IX, the living swim bladder may contain 

 oxygen at a pressure of 100 atmospheres without harm to the 

 cells lining its walls. These cells are apparently "acclimatized" to 

 the oxygen, just as the cells lining the stomach wall are acclima- 

 tized to hydrochloric acid. It is not improbable that the lungs are 

 capable of acquiring some degree of acclimatization or immunity 

 to the effects of a high pressure of oxygen ; but on this point there 

 are as yet no observations. 



