PREFACE 



THE making of this book has been a study in elimination. 

 It is, therefore, necessary at the outset to indicate the 

 limits of its scope. It is intended that it shall be used 

 with other books. Supplementary reading upon general 

 biology, human anatomy, food chemistry, and dietetics 

 is greatly to be desired. In the field of physiology itself 

 many fascinating topics are entirely ignored and others 

 treated in bare outline, with the purpose of subordinating 

 all else to the subject of nutrition. Chemical formulae 

 have been excluded from the text and used but sparingly 

 in the notes. 



A certain preliminary knowledge of elementary science 

 is assumed. The key-word of the following discussion is 

 " energy." The success of the reader in gaining clear con- 

 ceptions of what is presented will depend upon his famil- 

 iarity with the meaning of that term. It is essential that 

 he shall understand that energy is latent or potential in 

 those chemical compounds which are susceptible of oxida- 

 tion. He must have learned to recognize the possibility 

 of its unending transformation. The more readily he 

 thinks in terms of molecules, the more profitably he can 

 read these chapters. 



Miss Ruth Bryant, Instructor in Biology in Simmons 

 College, has borne a part in the work, which is to be de- 

 scribed as collaboration rather than assistance. 



P. G. S. 



BOSTON, MASS., 

 August, 1912. 



5 



