[macleod-page] oxygen UNSATURATION OF BLOOD 



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and the arterial blood definitely unsaturated with oxygen, 

 shown in Table I. 



This 



TABLE I 



It is probable that unsaturation of the blood realy occurs at higher 

 percentages of oxygen in the alveolar air than those recorded here, 

 but it is difficult to demonstrate it when this is above 10. In one 

 experiment in which the alveolar oxygen stood at 10. 9, the respirations 

 were greatly excited over the normal (97 per cent, increase) and 

 the arterial blood was 96. per cent, saturated with oxygen (Expt. 42) 

 but we have discounted this experiment because the cat was hyper- 

 excitable owing to the decerebration being decidedly in front of the 

 anterior corpora quadrigemina. 



In a previous paper it was pointed out that a certain increase 

 in breathing usually occurs within a few seconds after connecting the 

 tracheal cannula through valves with a closed system of wide bore 

 tubing and that this increase is probably accounted for in some way 

 by the slight resistance to the movement of air since it cannot be 

 related to increase in CO2 or deficiency of O2 in the air breathed. 

 In the present experiments this possible source of error has been 

 avoided by using the thin-walled rubber bag as described above. 

 When the bag contained air of normal composition its attachment to 

 the inspiration valve had no effect on the breathing. 



2. During the subsequent ten minute intervals of anoxaemia the 

 volume of air breathed may either increase or decrease, although the 

 percentage of oxygen in the inspired air has remained unaltered. It 

 is, therefore, important to compare the behaviour of the oxygen 

 unsaturation of the blood with these changes in respiration. This 

 is done in Table II. 



