PREFACE xi 



AUTHOR'S NOTE TO 1944 REPRINT 



Except for the addition of a few recent titles to the 

 bibliography this is a straight reprint of the second 

 edition which was brought up to date to 1936. Owing 

 to the war there has been insufficient advance in our 

 knowledge to warrant further revision. The reader 

 should, however, bear in mind that anj'' paragraphs 

 introducing a time factor have the year 1936 as reference 

 point and that any references to the " war " are to the 

 war of 1914-18. 



F.S.R. 



C.M.Y. 



