72 J. E. Kirk and T. J. S. Laursen 



where, 



A: = diffusion coefficient, 



Ci= concentration of solute on donor side at beginning 



of period, 

 C2=concentration of solute on recipient side at 



beginning of period, 

 ^3^ concentration of solute on donor side at end of 



period, 

 ^4= concentration of solute on recipient side at end of 



period, 

 A = area of membrane in cm. 2, 

 L=thickness of membrane in cm., 

 Vi and ¥2= volumes of solution in the two compartments 



expressed in ml., and 

 ^=time in minutes. 



Results 

 Aortic tissue 



Determinations have been made of the diffusion coeffi- 

 cients of nitrogen, oxygen, carbon dioxide, lactate, iodide and 

 glucose in experiments on 51 samples of intima preparations 

 and 50 samples of media preparations. The age of the indivi- 

 duals from whom the samples were obtained ranged between 

 ten and eighty years. 



The mean diffusion coefficients observed for these prepara- 

 tions are shown in Table I. The table further contains the 

 calculated values for the products: diffusion coefficient 

 X VMWXIO^ It will be seen from the table that a fair 

 agreement was found between the product values for nitro- 

 gen, oxygen and carbon dioxide, and that the product values 

 for these gases were over two times greater than the product 

 values for lactate and glucose. These findings might indicate 

 the presence in the aortic membrane of a set of smaller pores 

 (permitting the passage of compounds of MW 28 to 44) and a 

 set of larger pores (permitting the passage also of compounds 

 of MW up to 180). 



