CHAPTER VI 



The Effects of Want of Oxygen. 



In the higher organisms, as Paul Bert first pointed out, the im- 

 mediate cause of death of the body as a whole is practically always 

 want of oxygen, owing to failure of the circulation or breathing. 

 This fact arises from the circumstance that the body has hardly 

 any internal storage capacity for oxygen, but depends from 

 moment to moment for its supply from the air. We can deprive 

 the body for long periods of its external supplies of food or water, 

 or we can prevent for some time the excretion of urinary products 

 or even of carbon dioxide, but we cannot interfere with the supply 

 of oxygen to the blood without producing at once the most threat- 

 ening symptoms. Almost the only appreciable storage capacity 

 for surplus oxygen is in the lungs. In virtue of this small store 

 breathing can be prevented for about ij4 minutes in a man at 

 rest and previously breathing normally before urgent symptoms 

 of oxygen want appear ; but if the oxygen in the lungs and blood 

 is rapidly washed out by breathing pure nitrogen, nitrous oxide, 

 or other gas free from oxygen, loss of consciousness occurs almost 

 at once. Lorrain Smith and I found that even with quiet breathing 

 of pure hydrogen, so that some time was needed to wash out the 

 lungs, sudden and complete loss of consciousness was produced 

 within 50 seconds. 



Even when the oxygen supply, though not cut off, is insuffi- 

 ciently free, the ill effects develop rapidly, and may very soon 

 become serious. Hence few things are of more importance in 

 practical medicine than the causes and effects of want of oxygen. 



Want of oxygen in the systemic circulation may be produced 

 either by deficiency in the available oxygen in the arterial blood, 

 or by abnormal slowing of the circulation, so that too much of the 

 available oxygen is used up in the systemic capillaries. It will be 

 convenient to consider first the effects of want of oxygen or "an- 

 oxaemia," and afterwards discuss the various ways in which it 

 may be produced. 



The effects of anoxaemia can be observed most conveniently in 

 persons breathing air from which part of the oxygen has been 

 removed without the addition of any other gas producing by 

 itself a physiological effect; or in persons breathing pure air at 



