716 RALPH S. LILLIE 
such membranes as to the conditions in galvanic batteries.*° 
Bearing this principle in mind, we find that the electrical phenom- 
ena exhibited by living tissues, 1.e., systems in which electrolyte- 
solutions are separated by semi-permeable membranes—including 
those of stimulated muscle and nerve and dividing cells—lose their 
enigmatical character; they are special cases of phenomena long 
known to physical science and for which an adequate theory, due 
in its essential features to Nernst, has existed for some time. 
The indications that electrically polarized semi-permeable 
membranes play a fundamental part in vital processes are many 
and various. Cells are separated from their media by surfaces 
which are definitely semi-permeable. They also show a potential- 
difference against the medium, the demarcation-current potential, 
which has been repeatedly shown to undergo marked decrease 
when the surface-permeability increases, as at death or under 
the influence of cytolytic substances. Another proof of a surface- 
polarization, undergoing decrease with increase of permeability, 
is the well known fact that living cells are carried by an electrical 
current toward the anode, indicating that the cell-substance 1s 
negative, the adjacent water surface positive; when the cells die 
the rate of transport undergoes decided diminution.*! Again, 
electrical stimulation is a matter of ionic polarization, which can 
only occur at surfaces difficultly and unequally permeable to 
20 The type of membrane investigated recently by Haber and Klemensiewicz 
(Zeitschrift fiir physikalische Chemie, 1909, vol. 67, p. 385) is one permeable only 
to the ions of water. Such membranes, e. g. thin layers of glass or benzol saturated 
with water, have properties that appear in many respects to answer more closely 
to the biological requirements. Changes in the acidity or alkalinity of one of 
the solutions separated by such a membrane, amounting to a few ten-thousandths 
normal, may, especially if both solutions are nearly neutral, produce changes of 
potential comparable to those observed in living tissues during stimulation. 
The effects of increased permeability would in such membranes be identical with 
those produced at membranes of the type imagined by Ostwald. The most 
striking peculiarity of these membranes is their sensitivity to changes in the re- 
action of the adjoining solutions in the neighborhood of the neutral point. The 
fact that protoplasm and its normal medium lymph are typically neutral acquires 
new significance from this point of view. The following considerations apply 
to either type of membrane. 
31 An observation communicated to me by my colleague at Woods Hole, Dr. F. 
H. Pike, of Columbia University. I have since confirmed this observation, using 
portions of Spirogyra filaments. 
