RESPIRATION 



saturated by a foreign gas, such as carbonic oxide, with- 

 out any symptoms of want of oxygen arising. On the 

 other hand, where the amount of haemoglobin in the 

 blood is greatly reduced, as, for example, in anaemia, 

 there is no margin of oxygen-carrying power to draw 

 upon when oxidation in the tissues is increased, and 

 dyspnoea results upon slight exertion ; and if 70 per 

 cent, of the total blood be removed the deficiency of 

 oxygen is enough to cause death. 



If the tension of oxygen in the inspired air is in- 

 creased, the proportion of dissolved oxygen in the blood 

 is also increased. This is specially true when, owing to 

 disease of the lungs, the normal oxygenation of the blood 

 is interfered with. Physiologists who studied the subject 

 on perfectly healthy animals came to the conclusion 

 that oxygen inhalation would be of little use in disease, 

 for they found that even when the amount of oxygen in 

 the atmosphere was doubled the uptake of it was only 

 slightly affected.* 



We have here, however, an example of the danger of 

 the premature application of the results of physiological 

 experiment directly to the problems of disease. As a 

 matter of fact, an increase in the oxygen tension in the 

 air breathed does result in a considerable increase in the 

 amount of oxygen which enters the blood in conditions 

 of partial asphyxia, and the treatment of such con- 

 ditions by oxygen inhalation has justified itself by its 



* Thus, when air is breathed, arterial blood contains 18^ per cent, 

 combined 2 by vol., and 0'6 per cent, dissolved 2 by vol. 



When pure oxygen is breathed, arterial blood contains 18*7 per cent, 

 combined 2 by vol., and 3 per cent, dissolved O a by vol. HALDANE. 



