204 FINE-STRUCTURE OF PROTOPLASM II 



is calculated, i.e., the normality of the immobile framework anion equals 

 0.08 N. 



Meyer has proved the validity of his theory in numerous synthetic and 

 natural membranes. Undoubtedly it may therefore also be applied to the 

 cytoplasm. To this end, however, we must take into account not only the 

 ion mobility but also the lipid solubility. This is done by introducing the 

 distribution coefficients of the migrating substance between membrane 

 framework and outer liquid. If Ij^ and 1^ are the distribution coefficients 

 of the cations and anions respectively, the Donnan relation runs 



(y + A)y 



since the concentrations of the ions in the framework are increased or 

 decreased according as the distribution coefficients are larger or smaller 

 than I. The general permeability formula then takes the form 



"K _ Uk (a/4cMk 1a +A^ + A) 

 n^ Ua(V4c^1k1a + A2-A)' 



Although this formula has as yet hardly been applied to cytoplasmic 

 permeabiHty, I think it worthy of attention, as to a certain extent it 

 facilitates a synthesis of the theories of permeability in biology. Each 

 of the quantities occurring in it refers to a different principle of the 

 usual theories of permeability. The ion mobility U is a measure of 

 the filter resistance. In a hydrophilic framework with wide meshes, 

 Uj^ and U^ would be equal to the ion migration velocities in water. 

 By narrowing of the meshes, however, larger organic ions are im- 

 peded; and the filter effect will influence the quantities U. The effect 

 of the solubihty, in the first place the lipid solubiHty in the cytoplasm, 

 is accounted for by the distribution coefficients 1. The concentration 

 gradient applied is expressed by c and the selectivity constant A is 

 related to the electric phenomena accompanying the permeation. If 

 the framework of a membrane has a negative charge, i.e., if it behaves 

 like an anion, A becomes positive; in the reverse case, i.e., with a 

 positively charged framework, A is negative. For the amphoteric 

 cytoplasm the selectivity constant A must therefore be either positive 

 or negative, depending on the p„ of the nutrient. 



If the p^ value of the imbibing liquid lies above the isoelectric state 

 of the molecular framework, the cytoplasm behaves like an anion and 

 thus is permeable to cations. In this state, weakly basic substances Hke 

 amides (urea, methyl urea, malonic amide, etc.) will permeate more 



