226 RESPIRATION 



Our next experiments 16 were on various small animals 

 chiefly mice. Small animals are specially convenient, as their 

 blood becomes saturated within a few minutes to its maximum 

 extent for any percentage of CO in the air. These experiments 

 again gave an apparently higher oxygen pressure in the arterial 

 blood than in the alveolar air. When the percentage of CO was in- 

 creased, so that the animals began to show symptoms of consid- 

 erable oxygen want, the difference between arterial and alveolar 

 oxygen pressure became much greater. On the other hand, when 

 the animals were breathing a mixture of oxygen and CO there 

 was still a large apparent excess of arterial over alveolar oxygen 

 pressure. This result was a great disappointment to us, as we had 

 hoped that when oxygen was breathed, active secretion of oxygen 

 inwards would cease. The fact that it apparently did not do so 

 ought to have aroused our suspicions of the correctness of the 

 measurements. The phenomena observed when the oxygen per- 

 centage, or the barometric pressure, was diminished, led us, apart 

 from the measurements, to conclude that secretion of oxygen in- 

 wards became more active; but in our measurements of oxygen 

 pressure we were depending on the substantial correctness of 

 Hiifner's dissociation curve; and when this curve was subse- 

 quently found to be totally incorrect our measurements had also 

 to be abandoned as incorrect. 



During the next few years knowledge as regards the dissocia- 

 tion of haemoglobin had greatly increased, thanks to the work of 

 Bohr, Zuntz and Loewy, Barcroft, and others, as well as our own 

 work, as described in Chapter IV. Douglas and I now took up the 

 old subject again, but with far more complete knowledge of the 

 material we were dealing with. 17 Dr. Krogh had also kindly in- 

 formed me in a letter of some experiments he had made (subse- 

 quently published) 18 showing that in the blood of a rabbit the 

 relative affinities for haemoglobin of oxygen and CO were dif- 

 ferent from those in the ox ; and we found, as already mentioned 

 in Chapter IV, that this is not only so for different classes of ani- 

 mals, but also, and in a most marked degree, for different indi- 

 viduals of the same species. 



We therefore had to modify the method. Each animal was ex- 

 posed for a sufficient time to a definite percentage of CO in a 

 bottle, and then drowned in situ. Some of its blood was then 



19 Haldane and Lorrain Smith, Journ. of Physiol., XXII, p. 231, 1897. 

 " Douglas and Haldane, Journ. of Physiol., XLIV, p. 305, 1912. 

 "Krogh, Skand. Arch. /. Physiol., XXXII, p. 255, 1910. 



