84 THE NEW PHYSIOLOGY. 



is made evident by post-mortem examination of similar 

 fatal cases, as well as by the character of the sputum. 

 The lung alveoli contain large quantities of albuminous 

 liquid, and the alveolar tissues are swollen and pro- 

 liferating. The diagnosis is completed by the observa- 

 tion that on administration of oxygen the cyanosis 

 clears up and the circulatory and other symptoms 

 improve. By administering oxygen we largely increase 

 the percentage of oxygen in the lung alveoli, and thereby 

 increase in still larger proportion the diffusion pressure 

 of oxygen into the blodd. Under normal conditions 

 the partial pressure of oxygen is about 6 per cent, of an 

 atmosphere in human venous blood, and 13 per cent, in 

 the alveolar air, the difference being therefore 7 per cent. 

 With the presence of liquid and swelling of the alveolar 

 epithelium, the pressure difference present is not sufficient 

 to drive enough oxygen through to oxygenate the blood 

 at all completely. But we can increase the normal 

 pressure difference as much as ten or twelve times by 

 giving oxygen, so that the oxygen goes in far faster ; 

 and usually a quite moderate increase in the oxygen 

 percentage of the air suffices to remove the cyanosis. 

 The increase in the breathing multiplies by several 

 times the pressure difference which enables CO 2 to pass 

 out, so that escape of CO 2 is already provided for. 



What, now, are the effects of the want of oxygen 

 indicated by the cyanosis ? We can observe some of 

 these effects in mountain sickness, where the want of 

 oxygen, to which, without the smallest shadow of 

 doubt, mountain sickness is due, is produced by defi- 

 ciency in the oxygen pressure of the air. In this case 

 the want of oxygen is slight, but the nausea, headache, 



