12 PREFACE. 



to-day. A similar advantage may be expected to follow the inevitable over- 

 lapping of the topics assigned to the various contributors, since this has led 

 in many cases to a treatment of the same subject by several writers, who have 

 approached the matter under discussion from slightly varying standpoints, and 

 in a few instances have arrived at slightly different conclusions. In this 

 last respect the book reflects more faithfully perhaps than if written by a 

 single author the legitimate differences of opinion which are held by physi- 

 ologists at present with regard to certain questions, and in so far it fulfils 

 more perfectly its object of presenting in an unprejudiced way the existing 

 state of our knowledge. It is hoped, therefore, that the diversity in method 

 of treatment, which at first sight might seem to be disadvantageous, will prove 

 to be the most attractive feature of the book. 



In the preparation of the book it has been assumed that the student has 

 previously obtained some knowledge of gross and microscopic anatomy, or is 

 taking courses in these subjects concurrently with his physiology. For this 

 reason no systematic attempt has been made to present details of histology or 

 anatomy, but each author has been left free to avail himself of material of 

 this kind according as he felt the necessity for it in developing the physiolog- 

 ical side. 



In response to a general desire on the part of the contributors, references 

 to literature have been given in the book. Some of the authors have used 

 these freely, even to the point of giving a fairly complete bibliography of the 

 subject, while others have preferred to employ them only occasionally, where 

 the facts cited are recent or are noteworthy because of their importance or 

 historical interest. References of this character are not usually found in ele- 

 mentary text-books, so that a brief word of explanation seems desirable. It 

 has not been supposed that the student will necessarily look up the references 

 or commit to memory the names of the authorities quoted, although it is pos- 

 sible, of course, that individual students may be led to refer occasionally to 

 original sources, and thereby acquire a truer knowledge of the subject. The 

 main result hoped for, however, is a healthful pedagogical influence. It is too 

 often the case that the student of medicine, or indeed the graduate in medicine, 

 regards his text-book as a final authority, losing sight of the fact that such 

 books are mainly compilations from the works of various investigators, and 

 that in all matters in dispute in physiology the final decision must be made, so 

 far as possible, upon the evidence furnished by experimental work. To enforce 

 this latter idea and to indicate the character and source of the great literature 

 from which the material of the text-book is obtained have been the main 

 reasons for the adoption of the reference system. It is hoped also that t"he 



