MEMBRANE PERMEABILITY AND DRUG STRUCTURE 57 



2500X 

 PMV^e RT /J5= constant (7) 



where B = oil : water partition coefficient, and x = 

 number of unscreened CHg groups per molecule. 

 Table x shows the degree to which this relationship is 



TABLE X 



R MOLECULE 



CELLS OF Chora ceratophylla 



U 2 $00 X 



VALUES OF PM^^e "^ FOR MOLECULES PENETRATING INTO THE 



obeyed by molecules penetrating the cells of Chora cera- 

 tophylla. The adherence to the theoretical relationship 

 is sufficiently good for one to be able to calculate the 

 permeability to other molecules to a first approximation. 

 The fourth group of substances are those the main 

 resistance to the penetration of which lies in the in- 

 terior of the membrane. This group obeys the relation- 

 ship 



PMVi/B = constant. ( 8) 



Tables xi, xii and xiii show the degree to which this 

 relationship is in fact obeyed for the cells of Melosira, 

 Arhacia eggs and the rumen of the sheep. 



Several comments must be made upon these results. 

 First, the constants in the various equations just given 



