A Critical Study of the Pacts of Artificial 

 Fertilization and Normal Fertilization. 



By 



J. Gray, M.A., 



Fellow of King's College, Cambridge. 



With 1 Text-figure. 



Facts concerning the process of fertilization and of artificial 

 parthenogenesis have steadily accumulated during the past 

 thirty years, and although numerous suggestions have been put 

 forward as partial explanations of this imposing mass of experi- 

 mental evidence, yet there are only two theories which claim to 

 give an adequate picture of even a majority of the known facts. 

 These theories we owe to J. Loeb (24) and to F. E. Lillie (20). 

 According to Loeb, the activation of an unfertilized egg is 

 effected by the introduction into the egg of two substances, 

 (i) a specific cytolysin, which brings about the destruction of 

 the surface layer of the egg, and (ii) a substance which limits 

 or controls the destructive influence of the cytolysin. On the 

 other hand, Lillie holds that the union of the egg and sperma- 

 tozoon is only possible in the presence of a specific substance 

 or fertilizin which is secreted by the unfertilized egg ; if all 

 three elements are present fertilization and normal develop- 

 ment take place. 



Loeb's theory is based upon the facts of artificial partheno- 

 genesis ; Lillie's theory is based upon the behaviour of the 

 normal gametes. It is not surprising to find that each theory 

 encounters its chief difficulties when confronted with the facts 

 which constitute the main argument of its rival. Both theories 

 are essentially chemical, although the door is left open, at rare 

 intervals, to the intervention of physical factors. In 1915 (8) 

 I suggested that although the theories urged by E. S. Lillie (21) 



