730 RALPH S. LILLIE 
I do not propose to elaborate the above theory further at 
present. The foregoing analysis, whatever its defects in detail, 
indicates, I believe, that by taking account of the changes of poten- 
tial resulting from alterations in the permeability of electrically 
polarized membranes, certain characteristic phenomena of mitosis 
are susceptible of consistent physico-chemical explanation. The 
distinctive appearances presented by the process appear to depend 
essentially on the following conditions: that two concentric 
semi-permeable membranes, enclosing between them cytoplasm 
with its characteristic oxidative metabolism, undergo simultane- 
ously, in certain definite regions, alterations of permeability with 
accompanying changes in the potential-differences between the 
regions which they separate. Membranes of varying permea- 
bility thus play a fundamental réle in cell-division, as in the 
processes of stimulation, absorption, secretion, and conduction 
of stimuli. ie 
It is evident that such a system as the dividing cell presents 
many difficult physico-chemical problems. The situation is 
complicated by the chemical changes involved, some of which, 
including the energy-yielding oxidations, must be influenced by 
the changes in electrical potential at the surfaces. The mem- 
branes, in fact, are to be regarded as electrodes of changing 
potential; and by acting as such, as well as by altering the con- 
ditions of interchange, they must influence the course of the 
chemical reactions. The simple inorganic model imagined above 
is probably similar, in the purely electrochemical aspect, to the 
normal nucleated cell, while complications of a purely chemical 
nature are absent. It may thus serve to throw light on those 
physical features of the mitotic process which are dependent on 
changes of electrical potential at the surfaces. The nature of the 
metabolic processes in cell-division remains, however, as the 
essential problem, and it is probable that the facts required for 
its adequate solution are still largely unascertained. It is possi- 
ble that study of the relations between alterations in membrane- 
permeability and chemical changes in substances adjacent to the 
membranes will throw light on the nature and conditions of meta- 
bolic processes, not only in dividing cells but in cells in general. 
