718 RALPH §. LILLIE 
phenomena of the production of a system of cytoplasmic radia- 
tions and spindle-fibers appear in a new light. The arrangement 
of the colloidal material in dividing cells irresistibly suggests the 
figures due to polarization of suspended particles in electrical or 
magnetic fields, and this comparison has naturally been made by 
many. The hypothesis that electrical forces are actually con- 
cerned in these phenomena has, however, been accepted by few 
and with reservations, and alternative attempts at explanation 
have on the whole received more credence among biologists. 
As I have already remarked, the difficulty of accounting for the 
existence of potential-differences between different regions of the 
cells has been the chief obstacle to the acceptance of such views. 
This difficulty, since the rise of the ionic theory and the recog- 
nition of the part played by ion-liberating surfaces in galvanic 
cells, has, I believe, ceased to exist. It is only necessary to recog- 
nize that membranes unequally permeable to anions and cations 
may play a part essentially identical with that of the metallic 
surfaces in batteries. 
Evidence from many sides indicates that such membranes 
exist.” Furthermore, their existence is a necessary deduction from 
the ionic theory, which ascribes different diffusion-rates, different 
solubilities, and different velocities and powers of penetration tothe 
different ions arising from the dissociation of any electrolyte. I 
shall not therefore attempt further in the limited space at my dis- 
posal to justify the assumption that such membranes exist; this 
would be tantamount to justifying the ionic theory, which, in spite 
of certain apparent inadequacies which have been made the basis 
of sometimes violent attack, has today a stronger position than 
ever. Its fruitfulness, the criterion of value in any theory, is 
attested by the innumerable successful researches which have 
37 Cf. Ostwald: loc. cit.; Tammann: Zeitschrift fiir physikalische Chemie, 
1892, vol. 10, p. 255; Walden: ibid., p. 699; Bein: ibid., 1899, vol. 28, p. 439; Briin- 
ings: Archiv. fiir die gesammte Physiologie, 1903, vol. 100, p. 367; Schreber: 
Zeitschrift fiir physikalische Chemie, 1899, vol. 28, p. 79; Springmann: Annalen 
der Physik, 1896, vol. 51, p. 140. The phenomena of electrical endosmose also 
belong here in part. 
