IV 



PREFACE 



Research (now Secretary, AAAS Section Nd); Franklin C. McLean, 

 University of Chicago; and George Nichols, Jr., Harxard University. 



The cost of the color plate (facing page 218) was covered by a 

 grant from tlie Miami Vallev Laboratories of the Procter & Gamble 

 Companv, Cincinnati, Ohio. 



From the initial planning until the final preparation of subject 

 and author indexes, I have enjoved assistance bevond the hours of 

 duty from Mrs. Dorothy Good, Administrative Assistant, and Mrs. 

 Phyllis Lessin, Secretary, School of Dentistry of the University of 

 California, Los Angeles. 



I am grateful for the excellent cooperation of all the authors here 

 and abroad, and for other expert help in editing this volume. 



Each of the individual chapters that follow is concluded with a 

 summary, and the brief tabulation below mav serve to orient the 



SUMMARY OF CONTENTS 



