56 MEMBRANE PERMEABILITY AND DRUG ACTION 



in the interior of the membrane. In the first case a diffus- 

 ing molecule finds its passage through the membrane 

 dominated by the difficulty of passing either from the 

 water into the membrane, or from the membrane into 



TABLE VIII 



THE PERMEABILITY OF THE BACTERIUM 



Beggiatoa mirabilis to various 



MOLECULES 



TABLE IX 



VALUES OF PM^^ FOR DIFFUSION OF ANIONS 



THROUGH THE WALL OF THE RUMEN OF A 



SHEEP 



Acetate 



Propionate 



Butyrate 



5.8 

 5-3 



7-4 



water. In the second case, passing the interfaces is not 

 the limiting factor: the difficulty is in passing through the 

 interior of the membrane. The group of cases in which 

 passage through the cell membrane interface presents 

 the main difficulty obeys the relationship 



