362 E. Newton Han'ey 



tion of the arrows until checked by a second accumulation ot 

 reaction products and equilibrium is again attained. 



The n:en-;brane substance, in contact with sea-water, hardens, 

 (presumably an oxidation and comparable to the hardening of 

 silk in the air) thus forming a film. Some proteid substance 

 form.ed just behind the fertilization meir.brane (possibly a small 

 amount of the irembranogen diffuses out during increased per- 

 meability) would absorb sea-water and push the membrane out. 



A second increase in permeability would result in a repetition 

 of the process with the formation of a second membrane. 



The principle of Gibbs as applied by Metcalf* may help in 

 understanding how this reaction can proceed so readily at the 

 cell boundary. If, in a solution, a reaction occurs, one of the 

 products of which lowers the surface tension of the mixture, the 

 comir.encing of the reaction will be favored at the surface and the 

 products will collect at the surface. 



The role of the acetic acid in membrane formation would be the 

 increasing of the permeability of the egg membrane. This is pre- 

 sumably brought about by a combination of CH3COOH with 

 some of the surface proteids, a change with which increased per- 

 meability is assumed to be connected. At the end of this paper 

 I shall give some further general evidence for the permeability 

 theor)'.'^ 



The actual process of membrane formation as observed under 

 the microscope reveals nothing contrary to the above theory. 

 Herbsf^ in 1893 cut sections of eggs, fixed at intervals from immed- 

 iately after fertilization till the pushing out of the miembrane. 

 He describes the clear " Protoplasmasaum " becoming plainly 

 thicker just before a portion of it becomes lifted off and he inter- 

 preted this to indicate a secretion. It is not very resistant 

 first but later becomes quite firm. The pushing out from the 



^Metcalf: Zcit. Physic. Chem. 52 p., 1905; also Hober, Physikalische Cliemie d. Zelle uiui Ge- 

 webr, 2 cd. Leipzig, 1906, p. 209. 



■''See my pn-liiiiinary report (Year-book, Carnegie Inst., Washington, no. 8, pp. 119, 1909), and 

 Science, n. s., xxx, p. 776, 1909, also similar evidence by Lillie, R. S. (Biol. Bull., xvii, p. 202, 1909). 

 and McClendon (Science, n. s., xxx, p. 454, 1909). 



^Biol. Centralb., 13, 1893, p. 14. 



