The Plasmatic Membrane. 
191 
respectively. Lepeschkin provides evidence against this view by 
showing that the entry of water-soluble dyes and salts is diminished 
by the presence of narcotics, so that the lipoid and watery elements 
are not independent. 1 
Thus Spirogyra takes up enough methylene blue from a very 
dilute solution to be appreciably coloured in forty minutes, but if 
kept narcotised by 2-|% ether, added to the blue solution, then 
there is no colouration in forty minutes, this dye being rather 
insoluble in ether. If bismarck-brown is employed instead, which 
dye is very soluble in ether, then narcosis does not diminish the 
amount of stain taken up. On the uptake of any dye by dead 
cells, ether has no effect. 
Similarly by comparison of the isotonic coefficients for potassium 
nitrate and cane sugar in plasmolysing Tradescnntia epidermis, it 
is found that the permeability to the salt is much diminished in 
etherised cells in the ratio of 11 to 7. In ether-narcosis, dimi¬ 
nished permeability leads to increased turgor, and Spirogyra 
filaments are accordingly found to increase 0T% in length when 
placed in 2\% ether solution. 
Scattered up and down these four papers are a number of 
discussions and criticisms which bear on the constitution of the 
plasma membrane, and we may now give a summary account of 
Lepeschkin’s views on this subject. 
The plasma-membrane is defined as the part of the proto¬ 
plast which determines the selective permeability, but it is left an 
open question as to whether this is a thin superficial layer, or the 
whole thickness of the protoplasm. Various lines of evidence and 
Lepeschkin’s own coagulation experiments, however, prove that a 
visible outer layer has a less stability than the mass of the 
protoplasm. 
The plasma-membrane is obviously a complex colloidal 
structure and its selective permeability only holds while it is 
“alive.” It is fluid in nature, yet will coagulate spontaneously in 
time, like the temporary fluid phases of many inorganic precipi- 
1 Much of this argument is very fine-drawn and we have not 
sufficient physical knowledge yet to reason closely about the 
properties of such a complex surface-layer as the protoplast 
maypossess. Quite recently Hardy (Royal Society, May 16th, 
1912) has discussed the properties of a composite oil and water 
surface. 
