ELECTRICAL CONDUCTIVITY OF FERTILIZED AND UNFERTILIZED EGGS. 59 



Without wishing to dogmatize in any way as to the explanation of these 

 preliminary experiments, it may be pointed out that they may possibly 

 be due to either purely physical or purely chemical changes in the egg — 

 or to a combination of such causes. The egg in the unfertilized state is 

 remarkably impermeable to electrolytes, and can almost certainly be 

 regarded as being enclosed within a semi-permeable membrane. In its 

 unstimulated condition, this surface must necessarily be polarized. If 

 now this polarization be destroyed, the membrane must become more 

 permeable to ions than before. On this view the entrance of the sperm 

 •effects the depolarization of the plasma-membrane. After about fifteen 

 -minutes this membrane must become polarized again, but the mechanism 

 whereby this is effected is not at present clear. 



On the other hand, if the sperm carries an enzyme into the egg, which 

 acts on some constituent of the egg-cytoplasm, then a rise in conductivity 

 may occur as the result of the liberations of ions from unionized sub- 

 stances ; while a reversal of this reaction will have an opposite effect. 



It is hoped that further work will produce sufficient evidence to show 

 which of these two possibilities is the more probable explanation of the 

 experimental data, and a discussion of the results obtained by other 

 workers is therefore postponed. 



The expenses of this work have been partly defrayed by a grant from 

 the Government Grant Committee of the Royal Society. 



