In the successive phases of the development of the book various British 

 colleagues have been most kind in giving us their advice regarding the linguistic 

 side of the publication. In this respect the authors feel especially, and profound- 

 ly, indebted to Dr. Hugh Nicol, bacteriologist of Rothamsted Exper- 

 imental Station, for the untiring and devoted way in which he has accomplished 

 the most unselfish task of correcting the manuscripts from the point of view of 

 the language. In doing so, he has not only eliminated numerous short- 

 comings in English style and composition, but at several places his critical 

 suggestions - which were always to the point - - have greatly influenced the 

 redaction of the survey given. 



Delft, October 1940. G. VAN ITERSON JR. 



L. E. DEN DOOREN DE JONG 



A. J. KLUYVER 



