142 ArRrirFIcIAL 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 
1 Loeb, University of California Publications, Physiology, II, May, 1905. 
