PREFACE TO THE SECOND EDITION 



ASIDE from the chapter on Reproduction the new 

 material in this edition consists less in added facts than 

 in fresh ways of marshalling the data originally included. 

 I am in full agreement with my distinguished reviewer, 

 Professor W. M. Bayliss, of England, that it is only too 

 easy to sacrifice clearness of essentials to multiplicity of 

 details. The teacher whose task year after year is to 

 introduce successive classes to the fundamentals of his 

 subject will probably find with the passing of time that* 

 he is telling them less and less about the science, though 

 it may be reasonably hoped that he is telling it better. 



The distinction between elementary and advanced pres- 

 entations which was dwelt upon in the Preface of 1916 

 becomes more marked as the literature accumulates. 

 Recent contributions .to Physiology are largely of a 

 quantitative character. From this time forth the mas- 

 ters of the branch must be men thoroughly grounded in 

 Electricity and Physical Chemistry. Those of us who 

 once turned to Physiology with the serene confidence 

 that it would never involve us in any mathematics have 

 come to a time of disillusioning. But the unfolding of 

 the story in qualitative terms is a work which must still 



be done. 



P. G. S. 



BOSTON, MASS., 

 February, 1919. 



