RESPIRATION 249 



counted for from any probable rise in the pressure of CO 2 in the 

 venous blood. Examples of experiments in this direction are given 

 in the paper by Christiansen, Douglas, and myself. (2) It ap- 

 pears that men in good training and with the power of oxygen 

 secretion well developed are capable of standing a much higher 

 percentage of CO 2 in the inspired and alveolar air than other 

 men. In my experience with self-contained mine-rescue apparatus, 

 and similar devices, I have often been struck with the greater 

 sensitiveness to CO 2 of myself and other sedentary workers in 

 comparison with men in good physical training, although nearly 

 pure oxygen was being breathed. These observations suggest very 

 strongly that along with the power of oxygen secretion the power 

 of secretion of CO 2 is developed by muscular exertion. (3) In the 

 experiments of Paul Bert 35 on the blood gases when increasingly 

 high percentages of CO 2 were breathed by animals, it appeared 

 that with increase in the CO 2 percentage the CO 2 in the arterial 

 blood often showed little or no increase. It seems very dif- 

 ficult to explain these results apart from active secretion of CO 2 

 coming into play progressively, and particularly in view of the 

 experiments of Henderson and Haggard on the increased CO 2 - 

 absorbing capacity of the blood when excess of CO 2 is breathed 

 (Chapter VIII). 



In view of the absence, as yet, of direct measurements, it seems 

 unnecessary to discuss this question further; but I may point out 

 that just as the opponents of the oxygen-secretion theory have 

 been mistaken in drawing general conclusions from experiments 

 in which oxygen secretion was either absent or could not be dem- 

 onstrated, it is very probable that they have been equally mistaken 

 over secretion of CO 2 . Bearing in mind Johannes Miiller's argu- 

 ment as to the analogy between secretory activity and ordinary 

 metabolic processes, it seems quite likely that the active transport, 

 not only of oxygen, but also of CO 2 , is a phenomenon which oc- 

 curs in all living cells. 



Not only do oxygen and CO 2 diffuse through the lung epithe- 

 lium into or out of the blood, but also other gases, such as nitrogen, 

 hydrogen, methane, carbon monoxide, etc., so that their partial 

 pressures become exactly equal in the body and the alveolar air. 

 But how is it that oxygen is sometimes actively secreted inwards, 

 and that the oxygen pressure may be greater in the blood without 

 the oxygen leaking back by diffusion into the alveolar air just as 



"Paul Bert, La Pression barometrlque, p. 985. 



