58 MEMBRANE PERMEABILITY AND DRUG ACTION 



are not the same for every cell type. A different constant 

 is obtained for every type of cell, and the constant varies 

 with species as well as with cell type. Thus for any par- 

 ticular cell, before the permeability to a drug can be 

 calculated, it is necessary to know the permeability to 



TABLE XI 



VALUES OF PM^^^/B FOR VARIOUS SUBSTANCES PERMEATING INTO 



Melosira cells 



Propionamide 7.2 



Acetamide 2.0 



Glycol 6.1 



Glycerol 4.5 



Methylurea 2.3 



Urea 2.2 



several other molecules. A second point which must be 

 emphasised is that as drastic changes are made in the 

 structure of the molecule, it is likely that one will pass 

 from molecules falling into one of the groups given 

 above to molecules falling into another of the groups. 

 For example, group four consists mainly of molecules 

 which permeate cells rather rapidly whereas group three 

 consists of molecules which penetrate rather slowly. 



TABLE XII 



VALUES OF PM^'^-jB FOR VARIOUS SUBSTANCES PERMEATING INTO 



Arbada ova 



Butyramide 5.4 



Propionamide 5 . 9 



Acetamide 9.2 



Glycol II. 7 



1.8 



1 :2 Dihydroxy- 



propane 

 1:3 Dihydroxy- 



propane 2.8 



