262 LOADING UP 



It is worth while to look a little more closely at this problem. 

 In Chap. XXII., p. 247, is given a table of absorption coefficients 

 of the respiratory gases. These values of a' indicate the volumes 

 of gas at N.T.P. which will dissolve in 1 c.c. of water. Later in 

 the same chapter, figures which hardly differ from a were given 

 for the solubility of these gases in plasma, etc. The velocity of 

 diffusion depends not merely on the pressure gradient and on the 

 absorption coefficient of the gas, but also on a factor k the 

 diffusion coefficient, k is a constant for each gas and each 

 temperature. The appended table (from Loewy) will amplify this. 



TABLE XLII. 



DIFFUSION COEFFICIENTS. 



Temperature 16 C. 37 C. 



Oxygen - 1-62 1-68 



Carbon dioxide - 1-38 143 



Nitrogen - 1-73 1-79 



The product of a and k gives the diffusion rate in cm. per 

 24 hours through a layer of water, 1 cm. xl sq. cm. with a pressure 

 gradient of 1 atmos. For example, at 37 C. carbon dioxide has 

 a diffusion rate of 1-43 X 0-57 =0-81 5 cm. .per 24 hours. 



It has been found that k bears a definite inverse relationship 

 to the square root of the molecular weight of the gas. The result 

 of multiplying the diffusion coefficient by the square root of the 

 molecular weight of the gas is thus a constant for all gases. This 

 diffusion factor kjm has a value, for water, of -0649. 



The diffusion rate through lung substance, because of its large 

 content of lipoids and lipins must be greater than that through 

 water. Experiments with soap bubbles and with frogs' lungs 

 have confirmed this deduction. It has also been found that the 

 velocity of diffusion is absolutely unaltered by slight alterations 

 in the pH of the lung tissue. Loewy maintains that the rate of 

 diffusion is the same in dead and in living lung tissue. The 

 diffusion factor through lung has been estimated as 0-139. Ex- 

 periment has shown definitely that CO 2 passes just as readily in 

 either direction through the lung wall. This has been amply 

 confirmed by Krogh, who found that the direction of diffusion 

 depended entirely on the direction of the gradient of pressure, and 

 the rate of diffusion was regulated by the steepness of this gradient. 



The volume of gas diffusing per minute through one sq. cm. 

 of alveolar wall may be calculated from this formula : 



_ 

 ~ 



760 x/ra d 



