I/O RALPH S. LILLIE. 



and the surrounding medium. That the surface-tension between 

 two adjacent immiscible fluids may be so altered has long been 

 known ; the researches of Lippmann and Helmholtz have shown 

 that under these conditions the surface-tension is greatest when 

 the potential-difference of the two adjoining phases is zero, 

 and decreases in definite proportion as the potential -difference 

 increases. 1 The mutual repulsion characteristic of electrical 

 charges of like sign produces at the surface of contact a certain 

 expansive tension which opposes the normal surface-tension and 

 diminishes the latter by that degree. The deformation of the 

 charged mercury-drop, the expansion of the charged soap-bubble, 

 are familiar phenomena dependent upon diminution of surface- 

 tension so occasioned. It is thus possible that the surface-en- 

 laigement leading to cleavage may be a special instance of the 

 Lippmann-phenomenon ; if this is true we see at once the im- 

 portance of the electrolytes, since the production of a difference 

 of electrical potential between the two adjoining aqueous media 

 (egg and sea water, separated by a semi-permeable membrane) can 

 be accomplished only by a migration of ions. 



These ions must, under the conditions, be situated within the 

 egg ; the appearance of a charge at the surface of the latter must 

 therefore signify the gathering of a surplus of ions of one sign 

 in the superficial regions of the egg-protoplasm. This implies 

 the presence of a corresponding surplus of oppositely charged 

 ions in the interior of the egg. Hence the presence of a surplus 

 of ions of either sign in the peripheral region must iruply the 

 existence of a difference of electrical potential between the sur- 

 face and the interior of the egg ; and if the conditions of cleavage 

 are as we have supposed, evidence of such potential-difference 

 should be found at the time of cleavage. Is there any evidence 

 of the existence of such difference of potential, and, if so, how 

 'is the same to be accounted for ? 



In answer to the first question it may be said at once that 

 such evidence is by no means lacking, though of an indirect kind 

 and hitherto variously interpreted. It is seen, in my opinion, in 

 the typical appearances presented by the astral radiations and 



1 Cf. Ostwald, "Lehrbuch der allgemeinen Chemie," 2d Edition, Vol. II., pp. 920- 

 948. 



