RELATION OF PHYSIOLOGY TO MEDICINE. 85 



and extreme depression which result after a few hours' 

 exposure to the rarefied air are formidable enough 

 symptoms. Similar symptoms result from slight CO 

 poisoning. With more serious want of oxygen, as in 

 severe and prolonged exposure to CO, or to air very 

 deficient in oxygen, the effects are far more formidable. 

 There is very serious damage to the central nervous 

 system, and both capillary haemorrhages and large 

 haemorrhages may occur in the brain. The heart 

 becomes weak and dilated, with the mitral valve probably 

 incompetent. The kidneys and other organs may also 

 be injured ; and recovery, if it occurs, is slow and 

 gradual. Evidently, therefore, any serious want of 

 oxygen, if allowed to go on, is a source of great danger, 

 unless the patient has been gradually acclimatised to 

 it, as in some cardiac cases. The breathing, though 

 it is increased, gives no definite warning of this danger. 

 There is, for instance, no marked struggle for breath 

 when a man loses consciousness from CO poisoning or 

 an airman flies to a dangerous height. In phosgene 

 poisoning there is usually no great struggling for breath, 

 as the CO 2 , which stimulates the respiratory centre, can 

 easily be got rid of in the lungs. 



We can now see that the patient is in the gravest 

 danger and constantly going down the hill from the 

 cumulative effects of want of oxygen, but we cannot 

 undo the damage done to the exquisitely delicate alveolar 

 tissue ; much less can we replace it. We know, how- 

 ever, that if we can keep the patient alive, by obviating 

 secondary dangers, the lung epithelium will of itself 

 return to normal or something like normal. Now it 

 is evident that by the continuous administration of 



