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. O. 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 
vil 
