PREFACE TO SIXTH EDITION 



ALTHOUGH following soon after the fifth edition extensive revisions have been 

 incorporated in the present text. Three new chapters have been added to 

 meet general requests, on pH determinations, metabolic cycles and on chemo- 

 therapeutic agents and antibiotics. Some other chapters on biological aspects of 

 the subject have been largely re-written. 



The early chapters remain an introduction to the study of oxidation-reduction 

 potentials, but in the later chapters emphasis has gradually shifted in succeeding 

 editions to the implications and effects of oxidation-reduction conditions in metabolic 

 processes and living cells. This broadening of scope has been encouraged by widely 

 scattered correspondents on both sides of the Atlantic, and has necessitated the 

 epitomising of large subjects in small compass. In view of the cordial reception 

 afforded to previous editions, however, it appears unnecessary to apologise for the 

 policy of summarising relevant advances in varied fields. 



Apart from considerable internal reconstruction this edition differs from former 

 ones in its publisher. The author is indebted to Sir Allen Daley and the London 

 County Council for facihtating the transfer and to Mr. Charles Macmillan of Messrs. 

 E. & S. Livingstone for his help in the production in this new form. The opportunity 

 has been taken of improving the binding and it is hoped that the more robust covers 

 of this edition will meet with approval. 



The author's task of revision has again been lightened by the co-operation of 

 his wife and colleagues and by the encouragement of many other friendly research 

 workers. 



1950 L. F. H. 



(V) 



