Strom Company, Marcel Janinet, Herbert Paus, Hugh Spencer, and Karsten 

 Stapelfeldt. Although many of the illustrations are more or less self- 

 contained in that each conveys a complete idea, they, with their accompany- 

 ing legends, are intended to be integral supports for the text. Many are, of 

 course, convenient devices for conveying ideas of structure or of form; but 

 most of them involve ideas of process, of relationship, of historical tlevelop- 

 ment, or of logical development. In some cases they raise questions that 

 cannot be answered on a purely "factual" basis. All these graphic pieces are 

 intended to facilitate the work of the student, but for the most part they 

 cannot be lightly skimmed over like items in a picture book: they call for 

 close attention and reflection. 



We have been helped in our work by the many colleagues in the business 

 of teaching and by the many students through whom we think we have come 

 to understand the problems of the learner and his world. We wish to acknowl- 

 edge especially the helpful suggestions and criticisms and detailed information 

 and other material received from Dr. Louis I. Dublin, Chief Statistician, 

 Metropolitan Life Insurance Company; Dr. A. H. Ebeling, Lederle Labora- 

 tories; T. Swann Harding, United States Department of Agriculture; Dr. 

 Charles R. Knight, American Museum of Natural History; Professor Oliver 

 Laud, Antioch College; Algernon Lee, New York; Dr. Lloyd A. Rider and 

 Dr. Milton Hecht, Abraham Lincoln High School, Brooklyn; and Mrs. Emily 

 Eveleth Snyder, High School, Little Falls, New York. 



B. C. G. 



N. E. B. 



>c 



