142 Artificial Parthenogenesis and Fertilization 



eggs transferred from the benzoic acid after one minute all 

 formed a fertilization membrane. But those eggs which had 

 remained three minutes or more in the solution of benzoic 

 acid formed no membranes. But the eggs could no longer be 

 fertilized with sperm. 



The objection may be raised against these experiments that 

 the eggs are not killed by the fatty acid, but only made imper- 

 meable to spermatozoa. In order to test this objection, eggs 

 were first fertilized with sperm and then exposed to the action 

 of the acid mentioned. Fertilized eggs which had been longer 

 than two minutes in a 4/500 N butyric-acid solution were unable 

 to develop after transference to sea-water. We feel justified 

 therefore in regarding it as certain that the influence of the 

 chemical constitution of the acid upon its physiological action 

 is to be referred to the velocity of its diffusion into the egg. 

 (The latter influence is perhaps asserted in the sense that the 

 velocity of absorption of acid into the egg cell increases with the 

 increase of the coefficient of partition of the acid for oil and 

 water.) 



We must, however, give up the idea that the physio- 

 logical action of the acids is determined by the diffusion of 

 the hydrogen ion into the egg. Were that so, the activity 

 of the acid ought to correspond to the concentration of free 

 hydrogen ions, which is certainly not the case, as the inefficiency 

 of the strong acids shows. Hence these experiments also 

 furnish proof that the acids enter the egg cells in the form of 

 undissociated molecules. In my earlier publications* (1905) I 

 had already been led to the conclusion that in the causation of 

 membrane formation by acids it is not the hydrogen ion but 

 the undissociated molecules which come into play. That the 

 anions of the acids do not diffuse as such into the egg is shown 

 by the fact that the addition of the salt of a fatty acid, such as 

 sodium acetate, or sodium butyrate, to the sea-water causes as 



* Loeb, University of California Publications, Physiology, II, May, 1905. 



