12 RALPH S. LILLIE 
The question which I propose briefly to discuss in this section 
of the present paper is as follows: What relations can alterations 
in the permeability of the cell-membranes have to the mitotic 
process? Perhaps the most evident answer to this question, and 
one probably in large part correct, is the following: since (1) cell- 
division typically involves growth, which implies the incorpora- 
tion of surrounding food materials, and since (2) the plasma-mem- 
brane during the resting condition of the cell appears virtually 
impermeable to many diffusible substances essential to the cell, 
such as sugars, amino-acids, and neutral salts, periods of increased 
permeability are necessary in order to provide for the ready en- 
trance of outside materials into the cell. The increase in the per- 
meability of the nuclear membrane, leading typically to complete 
dissolution of this structure, is necessary to permit of free inter- 
change between nuclear and cytoplasmic regions.22 In general, 
increased permeability of the membranes facilitates or perhaps 
for the first time renders possible transfer of certain materials, 
particularly those normally kept apart by the membranes, be- 
tween the regions thus separated. 
The import of dissolved food-materials, however, like the sep- 
aration of dissolved substances in secretion (e.g., urea by the 
kidney), is not a mere matter of passive diffusion, but requires 
the performance of work; so that the simple assumption of an 
increase in permeability is insufficient entirely to account for the 
conditions. The nature of the active processes concerned in ab- 
sorption and secretion is still unknown; they are in all likelihood 
essentially the same in both functions; and from the analogy to 
other physiological processes in which the cell expends energy it 
seems probable that the production of differences of electrical 
potential between the surface layers and the interior of the cell 
is a fundamentally important factor. The view has, in fact, been 
entertained that cataphoresis plays a part in absorption,” al- 
though the experimental basis for this view is still inadequate. 
21 Compare Conklin: Journal of the Academy of Natural Sciences of Philadel- 
phia, 2d series, vol. 12, 1902, part 1; pp. 45 seq. 
22 For the first time by Engelmann: Archiv fiir die gesammte Physiologie, 
1872, vol. 6, p. 97. Cf. also Waymouth Reid: Journal of Physiology, 1901, vol. 
26, p. 436, and Héber: Archiv fiir die gesammte Physiologie, 1904, vol. 101, p. 
607. 
