

PREFACE TO THE SEVENTH EDITION. 



IN this, as in former editions, no fundamental change has been 

 made in the contents, arrangement of material, or the general 

 principles of presentation which were originally adopted. But in 

 the three years that have elapsed since the sixth edition the 

 natural expansion of physiological . and medical research has 

 yielded much new information. To incorporate the main feat- 

 ures of this added knowledge it has been necessary to make 

 many alterations. Throughout the work additions, substitutions, 

 and omissions have been used freely in order to bring the book 

 up to date as nearly as possible. 



It is now thirteen years since the first edition appeared. Dur- 

 ing this period the author has tried faithfully in the successive 

 editions to keep the book in line with our advancing knowledge. 

 It is not probable that he has been wholly successful in these 

 attempts, for the literature bearing upon the subject has increased 

 steadily in volume and complexity, but certainly he has not 

 altogether failed. The book has moved with the current of con- 

 temporary physiological thought, as a text-book must if it is to 

 be useful to its clientele of students. 



W. H. HOWELL. 



