THE PHYSIOLOGY OF FERI ILIZATION 171 



iV"/5oo NaOH. The same quantity of a single lot of eggs 

 was then added to each crystal and was fertilized with 

 the same quantity of a single lot of sperm. The percent- 

 age of eggs that segmented in each dish were as follows: 



Glass No. 



123456789 10 II 



Percentage 



o 2.5 8 22.5 45 53 84 92.5 88.5 89 o 



In the highest concentration of acid the unsegmented 

 eggs were devoid of fertilization membranes, thus unfer- 

 tilized, but in the highest concentrations of the alkali 

 the unsegmented eggs had membranes and were thus 

 fertiHzed, but cleavage was inhibited by the OH ions. 



It will be observed that the curve derived from the 

 percentages of eggs fertilized ascends regularly from the 

 acid to the alkaline end of the series. Very striking 

 demonstrations of the favoring effects of NaOH on 

 fertilization may be obtained from eggs that give only 

 a very low percentage of fertilization in normal sea- 

 water, but may give a very high percentage in alkalized 

 sea-water. 



The presence of alkali favors the reaction between 

 the egg and spermatozoon, probably because it tends 

 to make the plasma membrane permeable and thus to 

 permit a closer relation between the activable substance 

 of the egg and the activating substance of the spermato- 

 zoon; this favors entrance of the spermatozoon into 

 the egg. The use of a hyperalkaline medium to facili- 

 tate fertilization was first made by Loeb in a successful 

 attempt to produce heterogeneous hybridization, and 

 has since been widely extended for the same purpose. 

 It should be noted that the reaction is favored only in 

 the actual presence of the alkali; previous treatment of 



