346 J. DAVIDSON 



Another indication that proteins are present in abundance 

 in the plasma-membrane is fomid by Lepeshkin in the fact that 

 (as was shown by his experiments) the same concentration of 

 certain organic substances (ethyl alcohol, methyl alcohol, 

 aldehyde, etc.) are required to coagulate the plasma-membrane 

 in Spirogyra nitida and Tradescantia discolor as is required to 

 coagulate egg albumen J ^ 



Already Pfeffer^^ has advanced the theory that the plasma- 

 membrane consists largely of protein in view of the fact that 

 precipitates are formed in the protoplasm when ions of the heavy 

 metals are introduced. 



The presence of lipoids in the plasma-membrane is, according 

 to Lepeshkin, proven by experiments of Overton which shows 

 that narcotics which are very sparingly soluble in water are 

 readily taken up by the cell. The presence of lipoids (oil-like 

 substances) in the plasma-membrane is further proven by Lep- 

 eshkin himself when he showed that concentrations of certain 

 narcotics which cause coagulation in the plasma-membrane and 

 in egg albumen are inversely proportional to the solubility 

 coefficients of these substances in water and in olive oil.^^ 



Lepeshkin's views, with reference to the nature of the plasma- 

 membrane, do not in reality, differ much from Nathanson's, 

 in spite of his proclaimed opposition to him. He agrees with 

 him that lipoids are present in the plasma-membrane and that 

 they do not form a continuous layer. He disagrees with him 

 with reference to the regulatory powder of the cell. To Lepesh- 

 kin the entrance of substances into the cell is (as it is to Ruhland) 

 a matter of simple diffusion, and any substance which is soluble 

 in the plasma-membrane will continue to pass into the cell 

 until its concentration within the cell and in the surrounding 

 medium is equalized. He disagrees with Overton and Nathan- 

 son with reference to the entrance of the dyes into the cell, and 



3* Lepeshkin, W. W., Zur Kenntniss der Chem. Zusammensetsung der 

 Plasma-membrane. Ber d. deut. Bot. Ges. 29: 247-261. 1911. 



2^ Pflanzenphysiologie, 1. c. 



3« Lepeshkin, W. W., tjber die Einwirkung Anijsthesierender Stoffe auf die 

 osmotischen Eigenschaften der Plasma-membrane. Ber. d. deut. Bot. Ges. 29: 

 349-355. 1911. 



