Vlll PREFACE 



these he desires to express his thanks. He is especially 

 grateful to his friends, Dr. Eugene C. Woodruff, of Penn- 

 sylvania State College, and Miss Marion Sykes and Mr. 

 Worrallo Whitney, of the Chicago High Schools, for valu- 

 able criticisms and suggestions. 



The author desires likewise to thank the many in- 

 dividuals and firms who have so generously assisted him 

 in the procuring of illustrations. Among these are Drs. 

 (X C. Farrington and C. F. Millspaugh, of the Field 

 Museum of Natural History, Chicago; the International 

 Stereograph Co., Decatur 111.; Dr. S. W. Stratton, of the 

 Bureau of Standards, Washington; Dr. Orville Wright, 

 Dayton, Ohio; Mr. William D. Richardson, of Swift and 

 Company; Professor Frederick Starr, of the University 

 of Chicago; Professor Martha Van Rensselaer, of the 

 Department of Home Economics, Cornell University; and 

 many others whose names appear under the figures. 



The drawings for the illustrations have been made by 

 Messrs. William F. Henderson, Macknet Van Deventer, 

 Otto Roth, Alex. Van Praag, Milford Davis, and Leland 

 Smith, and by Miss Hila Ayres. The drawings for Figs. 

 88, 206, and some others were made by Miss Ruth Fuller, 

 To all of these the author hereby expresses his apprecia- 

 tion and gratitude. J. C. H. 



Decatur, Illinois. 



