CYTOPLASM 



199 



not apply to permeability investigations which are restricted to diffusion 

 studies (Barlund, 1929; Ullrich, 1934; Hofmeister, 1935; Marklund, 

 1936), in which the concentration gradient applied is the only potential and 

 no account need be taken of energy produced by the cell. Accordingly, the 

 investigations connected with the respiratory sorption of substances 

 (Steward, 1932, 1933; LundegArdh and Burstrom, 1933, 1935; Hoag- 

 LAND and Broyer, 1936; Arisz and Van Dijk, 1939; Reinders, 1940; 

 Brauner, 1943) are not considered as permeability studies. 



All permeability theories have in common that the resistance to 

 diffusion is located in the so-called plasmalemma or cytoplasmic 

 membrane, which is the outer boundary layer of the cytoplasm and 

 which is supposed to be either a 

 submicroscopic Hpidic layer, an 

 ultrafilter or a combination of both 

 these structures. This plasma- 

 lemma has never been detected as 

 an individual layer in the ordinary 

 microscope. Moreover the hyaline 

 ectoplasm of amoebae cannot be 

 regarded as a permanent structure, 

 since in amoeboid motion it can 

 temporarily change into granular 

 endoplasm. Nevertheless the hy- 

 pothetic skin must be present, 

 for micro-injection experiments 

 (Chambers, 1928) show that dye- 

 stuffs, whose entrance is opposed 

 by the surface, readily spread into 

 the bulk of the. cytoplasm. Col- 



lander (1937 b) regards this outer skin as a lipid film free of proteins, 

 and according to Danielli (1936) and Tornava (1939) it consists of 

 only two to four molecular layers, since, on increasing the surface by 

 endosmosis, semi-permeabilitv of certain cells suddenly disappears at 

 a certain surface size, and the cytoplasm begins to "leak". Curtis 

 (1936), on the contrary, has found with red blood cells that the semi- 

 permeable skin does not become "thinner" when stretched, but is 

 continuously repaired by material supplied by inner layers. Probably, 

 therefore, the plasmalemma does not represent a definite skin, but 

 only a boundary layer in which lipids accumulate. Sometimes this 



Fig. 1 1 5. Scheme of submicroscopic plasma 

 boundary in vegetable cells (from Scarth, 

 1942). Lipids dotted, w cell wall; e hya- 

 line ectoplasm, coated with plasmalem- 

 ma ; pg plasma gel of endoplasm ; ps plasrna 

 sol of endoplasm; k kinoplasm; t tono- 

 plast; V vacuole; s transvacuolar plasmic 

 strand; m myelin tube; p plastid. 



