STUDIES OF FERTILIZATION 549 



7. THE NECESSITY OF FERTILIZIN FOR FERTILIZATION 



It will be apparent from the preceding facts and considerations 

 that the fertihzin answers some of the requirements of a binding 

 hnk between ovum and spermatozoon. When we consider the 

 extraordinary activity of the unfertilized egg in its secretion, and 

 the equally extraordinary avidity of the spermatozoa for it, one 

 cannot escape the conviction that it must be a link in the normal 

 fertilization process. When, moreover, one finds that the egg 

 contains a more centrally located substance that can occupy the 

 same combining group as the sperm, one seems to have before 

 one, a view of a mechanism for preventing polyspermy. 



I adopted, then, the working hypothesis that this substance 

 is necessary for fertilization and there followed immediately 

 three corollaries, viz : (1) If it were possible to extract this sub- 

 stance from eggs, they should no longer be capable of fertilization ; 

 (2) fertilized eggs are incapable of uniting again with spermatozoa, 

 hence, if the hypothesis is correct, they could no longer contain 

 free fertilizin; (3) eggs in which membranes have been formed by 

 methods of artificial parthenogenesis become incapable of fertili- 

 zation; such eggs must also, therefore, be devoid of free fertilizin 

 after they have reached the non-fertilizable condition if the 

 hypothesis is correct. These consequences of the theory were 

 actually found to be true. 



a. Fertilization of washed eggs 



The only way of which I could think of extracting the fertilizin 

 from the eggs without injury, is the method of repeated washings. 

 But we have seen (tables 2 and 3) that it is actually impossible to 

 remove all the fertilizin from a mass of eggs by any number of 

 washings, for the eggs continue to produce it until they go to pieces 

 However, the quantity produced in successive washings slowly 

 diminishes. Therefore, we might expect on the basis of the the- 

 ory, that there would be a gradual reduction of tjie percentages 

 of eggs fertilized after many repeated washings. This actually 

 occurs, as table 4 shows. It might also be anticipated that as 



