348 J. DAVIDSON 



of the plasma-membrane. Why not assume the view point of 

 Nathanson, viz., that the aniline dyes enter by the same pas- 

 sage way? The fact that the aniline dyes are soluble in water 

 need not be considered since the aniline dyes referred to by 

 Overton are so much more soluble in lipoids than in water. Their 

 solubility in lipoids is, perhaps, another condition for their 

 accumulation. 



It is safe therefore to state that there is no essential difference 

 between Nathanson's conception of the plasma-membrane and 

 that of Lepeshkin. The latter has only gone a step farther by 

 trying to get an insight into the physical state and chemical 

 composition of that part of the plasma-membrane which the 

 former simply . terms as protoplasm. The essential difference 

 in the views of the two investigators is their relation to the regula- 

 tory power of the cell as it is understood by Nathanson, but this 

 difference does not follow directly from their respective con- 

 ceptions of the plasma-membrane. 



It is, however, very evident that both investigators relegate 

 the lipoids of the plasma-membrane to a secondary position 

 among the factors conditioning the selective properties of the 

 cell with reference to permeability. 



SUMMARY 



(1) The subject of the existence of special plasma-membranes 

 is very little discussed in the literature and the meager evidence 

 at our disposal is too indefinite and too indirect to enable us to 

 draw any conclusions. 



When the term plasma-membrane is used in the literature 

 it may refer to the entire cytoplasm as well as to a special mem- 

 brane. 



(2) The discussion of the subject of selective permeability 

 of living cells and of the mechanism of diosmosis is entirely 

 speculative and the evidence offered in favor of any of the 

 various theories advanced is oo indirect to allow of any con- 

 clusions. 



(3) The lipoid theory as it has been formulated by Overton 

 is intrinsically contradictory, and the modifications of Nathan- 



