

The acquisition of oxygen by the blood in the lung 191 



but in this particular case p = 760 mm. and since the fluid is saturated with the gas 

 at 760 mm. the amount of gas which is dissolved in 1 c.c. of the fluid is a, the 

 coefficient of solubility, or the absorption coefficient of the gas in the fluid. Substi- 

 tuting 760 for p, and a for , our equation therefore becomes 



y = aj3. 



Now since a, /3 and y are all coefficients, that is to say constant quantities, we 

 may, in any further consideration of the subject, replace /3 by yja, thus getting rid of 

 the evasion coefficient in favour of a which is easily determined experimentally. 



(d) To calculate the volume M of a stream of gas passing per minute into a 

 fluid in which the concentration of the gas is , the pressure of the gas in the fluid is 



p', and without the fluid p. 



M=g-b, 



i.e. the difference between the amount of gas which passes into the surface and that 

 which passes out. 



760 



760 a 

 in the present case = p'/760 ; substituting this value we get 



(<?) For the human lung, M for a person not actively employed may be taken as 

 400 c.c. a minute, s as 90 x 10 4 sq. c. y was calculated by Bohr as being '012, p as 105 mm., 

 and therefore the only unknown factor in the equation is p'. Now taking these 

 figures, the difference between p and p' is about 25 mm., and therefore p' is about 

 80 mm. 



According to this calculation which contains nothing but mechanical reasoning, 

 the tension of oxygen in the fluid with which the epithelial cells of the lungs have to 

 deal cannot be more than 80 mm. or about 1 1 % of an atmosphere, i.e. is lower than 

 all computations of the tension of oxygen in the arterial blood as made by the 

 aerotonometer ; and the calculation was therefore regarded by its author as the final 

 and convincing proof of the secretion of gas by the epithelial cells from the place of 

 lower to the place of higher tension. 



We may summarise the results obtained by the use of the invasion 

 and evasion coefficients, as follows : 



(1) According to Bohr's statement of the diffusion theory, the 

 pressure of oxygen in the capillary would, apart from secretion, 

 be less than that in the alveolar air by at least the amount which 

 the invasion coefficient demands and which is measurable. 



(2) The difference between the two becomes greater in direct 

 proportion to the oxygen used by the organism. 



(3) The evasion coefficient of CO 2 is such that the difference 

 between C0 2 pressure in the lung, and in the blood of the pulmonary 

 capillaries, is immeasurably small. Figure 98, given by Krogh, 



