Ill 



THE FORCES ACTING IN THE TRANSPORT 



OF OXYGEN (AND C0 2 ) 



THROUGH LIVING TISSUES 



When in a living cell oxygen is used up by metabolic processes 

 its concentration is lowered and oxygen molecules will tend 

 to diffuse towards the place. Similarly the C0 2 produced by 

 the processes will tend to diffuse away. When blood posses- 

 sing a higher oxygen tension and a lower C0 2 tension is 

 carried past the cell all the time, the conditions for a regular 

 exchange are established. 



To the respiratory organs this blood arrives with an oxygen 

 deficit and a surplus of C0 2 , and conditions for a diffusion 

 exchange with the outside medium are normally present also 

 in this case. 



A complete solution of the problem is not obtained, how- 

 ever, by these simple qualitative considerations. It remains 

 to be made out whether the transport mechanisms are quanti- 

 tatively sufficient and whether other mechanisms can be 

 shown to exist. Certain physiologists (Chr. Bohr, J. S. Hal- 

 dane) thought they could demonstrate an active secretion of 

 oxygen from the air in the lungs into the blood, active accord- 

 ing to Haldane (1922, pp. 208-257) during muscular work 

 and after acclimatization to low oxygen pressures. Their 

 evidence was inconclusive, however, and the only place where 

 oxygen secretion has been shown to exist is in the gas gland 

 of the swimming bladder of many fishes where it is bound 

 up with very peculiar anatomical structures. 1 It is a strong, 

 but not a conclusive, argument for diffusion and against 

 active secretion that in the lungs of a small number of animals, 

 including man, and in the tracheal gills of dragon fly larvae 



1 It is probably present also in the gas bladder of several invertebrates and 

 perhaps in the protozoon Arcella (Haldane, 1922, p. 216). 



17 



