PROPERTIES OF PROTOPLASMIC MEMBRANES 137 



show osmotic action (semi-permeability) if only its 

 pores were sufficiently minute. In fact, Thomas Graham 

 observed many years ago (1854) that certain fine-grained 

 porcelains had definite osmotic action. Recently the 

 pore-diameters of osmotically acting porcelain disks 

 have been investigated by Bigelow and Bartell/ and 

 well-marked osmotic effects were found when the pores 

 had a diameter of the order o. 2-0.3 5/x.^ 



In general we may conclude from such facts that in 

 living semi-permeable membranes the degree of porosity 

 is low; i.e., the interspaces between the water-insoluble 

 colloidal particles forming the structural material are 

 at least as small as in porcelain and probably smaller, 

 since Bartell's membranes are not completely semi- 

 permeable. The physical conditions are probably closely 

 comparable with those existing in well-supported precipi- 

 tation-membranes of copper ferrocyanide, such as Morse 

 employed. In plasma membranes, however, variations 

 in the subdivision of the colloidal constituents may cause 

 variations in the size of the interspaces, and hence in the 

 permeability. The progressive deterioration to which 

 artificial colloidal membranes are subject in the pres- 

 ence of electrolytes is apparently prevented in Hving 

 membranes by compensatory factors dependent on me- 

 taboKsm; presumably any interruptions of continuity are 

 at once automatically repaired by the formation or 

 deposition of new structural material (see below under 

 stimulation) . 



^Bigelow, Journal of the American Chemical Society, XXIX (1907), 

 1675; Bartell, Journal of Physical Chemistry, XV (191 1), 659, and XVI 

 (1912), 318. 



^ Bartell. loc. cit. (191 2). 



