RESPIRATION 265 



after previously expiring deeply. After two seconds part of the 

 air in the lungs (about i^ liters) was expired, so as to obtain a 

 sample of alveolar air. The rest of the breath was held for five 

 seconds and a second sample of alveolar air was then taken. If 

 these two samples gave practically the same percentage of CO2, 

 the CO2 in the alveolar air was evidently in pressure equilibrium 

 with the CO2 of the oxygenated venous blood. If too much CO2 

 were present in the alveolar air the second sample would contain 

 less CO2 than the first, and if too little, more. We were thus using 

 the whole of both lungs as an aerotonometer. For any particular 

 person it was easy to find the mixture which gave equilibrium. 

 With the help of Figure 26 (Chapter V) we could then calculate 

 the CO2 content of the venous blood and the true value of the 

 venous CO2 pressure. We could also calculate how much CO2 the 

 blood had taken up in passing round the body if we knew 

 the normal alveolar CO2 pressure. The following table shows the 

 results obtained during complete rest in a sitting position with the 

 four subjects investigated. 



Reference to Figure 26 shows that on an average the venous 

 blood had only-taken up about 24 per cent of the CO2 which it 

 would have taken up if all its available oxygen had been used up. 

 Hence the blood had only lost about 24 per cent of its oxygen in 

 passing round the circulation; and in the three male subjects the 

 proportion lost was only about 21 to 22 per cent. This indicates a 

 much faster circulation rate during rest than the nitrous oxide 

 method had shown. 



At the outbreak of war. Dr. Douglas and I were engaged 

 in carrying these experiments further; but as he volunteered at 

 once for active service they were interrupted; and owing to the 

 disorganization following the war they are not yet completed, 

 though I was able to carry them on up to a certain point with 

 help from Dr. Mavrogardato, and to communicate a number of 



