PREFACE Vll 



College, who have read the manuscript in whole or in part 

 and who have offered many helpful suggestions. I am 

 grateful to those who have written chapters which have 

 been included in the text, and which appear under their 

 names, and to those who have furnished illustrations, to 

 whom credit is given in the list of illustrations. I wish 

 also to express my appreciation to my wife, Inez Van 

 Sickle Livingston, for her constant assistance in preparing 

 the manuscript for the press. 



GEORGE LIVINGSTON. 



Ohio State University, 

 Columbus, Ohio. 



