164 



RESPIRATION 



ished, the oxygen pressure in the arterial blood remains normal, 

 and as a consequence the respiratory center does not rapidly fail 

 in the same manner as it does when the arterial oxygen pressure is 

 very low, as explained in Chapter VI. This characteristic seems to 

 be common to all forms of anoxaemia in which the arterial oxygen 

 pressure remains about normal, including anoxaemia due simply 

 to a failing heart. 



If the action of CO were simply to diminish the oxygen- 

 carrying power of the haemoglobin, without modification of the 

 properties of the remaining haemoglobin, the symptoms of CO 

 poisoning would be very difficult to understand in the light of 

 other knowledge. Thus a person whose blood is half-saturated 



20 



Pressure of 2 in Mm. of \\g. 



30 40 50 6.0 70 



80 



90 



g 







&4%526272& 91 



Pressure of 0, in % of an atmosphere 



Figure 52. 



Curve I, o per cent saturation with CO; II, 10 per cent; III, 25 per cent; 

 IV, 50 per cent; V, 75 per cent. 



with CO is practically helpless, as we have just seen ; but a person 

 whose haemoglobin percentage is simply diminished to half by 

 anaemia may be going about his work as usual. Miners may be 

 doing their ordinary work though their haemoglobin percentage 

 is reduced to half or less by ankylostomiasis ; and women may be 

 going about their duties with their haemoglobin percentage re- 



