548 THE RESPIRATORY EXCHANGE 



These experiments are entirely in favour of the secretory theory, 

 and, if there should be no sources of fallacy in the method, would 

 decide the question as regards the absorption of oxygen in the 

 lungs. The criticisms have been chiefly supplied by the observers 

 themselves, and have been by them subjected to the test of experi- 

 ment. It might be that the carbon monoxide was not absorbed 

 by diffusion alone, and thus the method would be nullified ; it 

 appears, however, that the lungs exert no selective action in this 

 case, for the absorption ceases when the relative saturation of 

 the blood corresponds to the partial pressure of the gas inspired. 

 Experiments by Haldane show that carbon monoxide is not 

 oxidised in the body. The exactness of the data for the absorption 

 of carbon monoxide under different pressures may be questioned, 

 for the results obtained by Haldane and Lorrain Smith are exactly 

 double the values found by Hiifner, and are also higher than those 

 obtained by Bock. In the latter case the lack of agreement may 

 be due to the difference in the strength of the solution of haemo- 

 globin, but this will not hold in the case of Hiifner's experiments, 

 and in any case raises the question whether solutions resemble 

 the normal blood in their power of absorption. Haldane's colori- 

 metric method for the estimation of carboxy-hsemoglobin has been 

 shown by Haldane and Lorrain Smith to be liable to error, for 

 bright day-light has a most marked action in diminishing the 

 stability of the combination. Another important point is whether 

 an animal with 40 or 50 per cent, of its haemoglobin saturated 

 with carbon monoxide can be considered normal. Bohr, while he 

 hails these results as some of the strongest evidence in favour of 

 the secretory theory, yet maintains that the high pressures of 

 oxygen in the arterial blood are due to an abnormal increase in 

 the activity of the pulmonary epithelium, and the experiments 

 of Haldane and Lorrain Smith themselves show that want of 

 oxygen acts as a stimulus to the further absorption of oxygen. 

 Be this as it may, the results would still show that diffusion does 

 not explain the phenomena, and that the animals can under the 

 conditions of the experiment secrete oxygen. 



Further evidence in favour of the secretory theory can be 

 found in the presence in the swimming-bladder of fishes of almost 

 pure oxygen under pressures so high as to be beyond explanation 

 by the ordinary laws of diffusion. This interesting subject is 

 discussed by Leonard Hill in another part of this work. 



