2O6 RALPH S. LILLIE. 



according to Nernst's formula l may be estimated from the follow- 

 ing values : 



// v RT c<> 

 E -In-. 



u + v q c l 



Generally, therefore, the greater the difference between the two 

 ionic velocities the greater the potential difference across the 

 boundary; hence this will be maximal with complete imperme- 

 ability to the anion, since then its velocity is reduced to zero at 

 the membrane and u vju -f v becomes unity. Normally, how- 

 ever, there is probably a certain permeability to the anion, since 

 carbonic acid is continually evolved from living cells, although 

 slowly in a state of rest ; the potential difference in resting cells 

 may thus be supposed to approach but not to reach the maxi- 

 mum. If then the permeability undergoes an increase so that 

 anions may penetrate the membrane with considerable freeness, 

 i. c,, with increased velocity, the value of n vjn -f i> and also 

 of cjc l will decrease ; the result will be a fall of the potential 

 difference across the surface. The extent of this fall will obviously 

 depend on the degree of the increase in permeability and may 

 show a considerable range of variability. 



With decrease in the potential difference the surface-tension 

 must undergo a corresponding increase ; this increase in surface- 

 tension is, on the present theory, the main condition of the form 

 change in cell-division. Other changes of form may naturally 

 be similarly conditioned ; irregular form changes are frequent in 

 unfertilized eggs in which division is induced by the artificial 

 parthogenetic methods ; regular cleavage would require a sym- 

 metrical distribution of the areas of increased permeability with 

 reference to the future cleavage plane. 



In agreement with the above view of the nature of the chemi- 

 cal effects of stimulation, the initiation of the characteristic series 

 of chemical processes in cell-division is to be referred to a dis- 

 turbance of chemical equilibrium in consequence of the more 

 rapid loss of certain materials, perhaps simply carbon dioxide, 



1 is potential difference in volts, u velocity of cation, -' that of anion. R gas 

 constant, T absolute temperature, q quantity of electricity (coulombs) carried by a 

 monovalent gram-ion, In natural logarithm, <-j and c, 2 concentrations of the dissociated 

 part of the electrolyte on opposite sides of the boundary surface, The ions are as- 

 sumed to be monovalent in this form of the formula. 



