PREFACE 



In 1909 the author published a book entitled Die chemische 

 Entwicklungserregung des tierischen Eies (Springer, Berlin), in 

 which he gave an account of his experiments on artificial 

 parthenogenesis. The object of these experiments was the 

 substitution of physicochemical agencies for the mysterious 

 complex "living spermatozoon." The book has been trans- 

 lated into English by Mr. W. 0. R. King, but, owing to the 

 new observations since made, the author has found it necessary 

 to revise and enlarge the translation. 



The book gives a survey of the methods by which the 

 unfertilized egg can be caused to develop into an embryo 

 and the conclusions which can be drawn concerning the mechan- 

 ism by which the spermatozoon produces this effect. The 

 theory, which the author published in 1905 and 1906, that at 

 least two factors are involved in this process, namely, one 

 which brings about a change in the surface of the egg (the 

 essential factor), and a second, corrective factor, seems to 

 explain all the phenomena observed in the new territory and 

 has proved a reliable guide. 



In developing the new field of investigation, the writer 

 endeavored to select those variables and methods which would 

 lend themselves to a quantitative treatment. 



The problem of fertilization is intimately connected with 

 many different problems of physiology and pathology. We 

 may mention, among others, the natural death of the egg cell 

 and the prolongation of its life by fertilization; the fertiliza- 

 tion of the egg by foreign blood and the immunity of the egg 

 to blood of its own species; the relations between heterogeneous 

 hybridization and artificial parthenogenesis, between fertiliza- 

 tion and cytolysis, and between permeability and physiological 



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