PREFACE TO THE EIGHTH EDITION. 



During the three years that have elapsed since the last edition 

 of this book much has been added to our knowledge by the results 

 of physiological research, and, on the other hand, something has 

 been subtracted by the modification or elimination of untenable 

 statements and theories. There has been no fundamental change, 

 no epoch-making discovery, but there has been the usual con- 

 stant shifting in points of view as our knowledge has widened and 

 as the results of the advances in other branches of science have 

 found their application in physiology. 



The author has attempted, as far as possible, to follow and 

 interpret these changing phases and thus keep the book in touch 

 with current progress. Matter that seems now to be irrelevant 

 has been stricken out, and the newer ideas and terminology have 

 been introduced. 



Some new figures have been added and an effort has been 

 made to emphasize the hygienic application of physiology wherever 

 it seemed to fit in appropriately in the plan of presentation. A 

 full treatment, however, of this side of the subject requires a text- 

 book of its own. 



The science of physiology has found most important applica- 

 tions in the fields of pathology and clinical medicine, but, un- 

 fortunately, its more natural relations to the maintenance of the 

 health of the individual have been neglected. Publications upon 

 personal hygiene are in large part unscientific compilations that 

 serve to perpetuate baseless traditions or to disseminate the 

 vagaries of irresponsible faddists. A critical scientific presenta- 

 tion of the subject is obviously a difficult undertaking, requiring 

 a wide and sound knowledge of pathology and medicine as well as 

 physiology, but something of the kind is much needed to clear the 

 ground and to indicate the directions along which experimental 

 inquiries should be made. 



W. H. Howell. 



