vi The Biochemistry of Semen 



well as non-mammalian physiology, selecting examples from 

 species as far apart as man and the sea-urchins, and occasion- 

 ally, introducing plants as well. I have done my best to dis- 

 tinguish between established fact and tentative hypothesis, and, 

 as far as possible, have refrained from the tendency, currently 

 prevalent among workers in this field, to assign to every newly 

 discovered chemical constituent of semen a major role in the 

 process of fertilization. 



I wish to acknowledge gratefully the help of those who gave 

 me permission to reproduce plates and figures. In particular 1 

 wish to extend my thanks to Dr. C. R. Austin (Sydney), Dr. 

 J. L. Hancock (Cambridge) and the Cambridge University 

 Press for Plate I, to Prof. L. H. Bretschneider and Dr. Woutera 

 van Iterson (Utrecht) and the Nederland Academy of Science 

 for Plate II, to the Royal Society for Plate III, to Lord Roth- 

 schild (Cambridge) for Plate IV and for reading the manuscript, 

 to the Royal Society of Edinburgh for Fig. 2, to Dr. E. Blom 

 (Copenhagen) and the Skandinavisk Veterinartidskrift for Fig. 3, 

 to Dr. C. Huggins (Chicago) and the Harvey Society of New 

 York for Fig. 5, to Dr. L. Jacobsson (Goteborg) and the Acta 

 Physiologica Scandinavica for Fig. 11, and to the Cambridge 

 University Press, Messrs. Churchill and Messrs. Macmillan for 

 permission to reproduce Figs. 6-10, 12-14 and 16, from the 

 Biochemical Journal, the Journal of Agricultural Science, and 

 Nature, and Plate IV, from theCiba Foundation Symposium on 

 Mammalian Germ Cells. I should also like to thank Miss P. A. 

 Northrop for helping me in the preparation of the typescript. 



