86 PHYSIOLOGY AND NATIONAL NEEDS 



First it leads to increased excitability of the 

 nervous system, then later to decreased activity, 

 and so to the drowsiness which comes as a relief 

 to the patient, but as a danger-signal to the 

 physician. 



Not only is the nervous system thus acted on by 

 the want of oxygen, but the heart also suffers. 

 First its rate is increased, then its action begins to 

 fail, blood is no longer driven onwards, and the 

 patient may pass into the condition of collapse 

 with the ashy grey face and blue lips that so 

 frequently precede death. 



Want of oxygen is the prime cause of all the 

 symptoms. 



How can this condition be relieved ? 



Ordinary air contains about one-fifth of its bulk 

 of oxygen. If the air can get freely into the air- 

 sacs this proportion of oxygen is sufficient, but 

 if a large number of air-sacs are full of fluid, the 

 best chance is to give a much higher proportion of 

 oxygen to the sacs which are still available, or to 

 enable it to be taken up by the fluid, and which 

 may thus reach the blood. 



Inhalations of oxygen were recommended by 

 Haldane on these physiological grounds, and have 

 proved of the utmost value in tiding the patient 

 over this critical stage till the natural drainage 

 from the lungs has removed the fluid from the 

 air-sacs. 



