PREFACE. 



In the preparation of this book the author has endeavored to 

 keep in mind two guiding principles: first, the importance of 

 simplicity and lucidity in the presentation of facts and theories; 

 and, second, the need of a judicious limitation of the material 

 selected. In regard to the second point every specialist is aware 

 of the bewildering number of researches that have been and are 

 being published in physiology and the closely related sciences, and 

 the difficulty of justly estimating the value of conflicting results. 

 He who seeks for the truth in any matter under discussion is often- 

 times forced to be satisfied with a suspension of judgment, and 

 the writer who attempts to formulate our present knowledge 

 upon almost any part of the subject is in many instances obliged 

 to present the literature as it exists and let the reader make his 

 own deductions. This latter method is doubtless the most satis- 

 factory and the most suitable for large treatises prepared for the 

 use .of the specialist or advanced student, but for beginners it is 

 absolutely necessary to follow a different plan. The amount of 

 material and the discussion of details of controversies must be 

 brought within reasonable limits. The author must assume the 

 responsibility of sifting the evidence and emphasizing those con- 

 clusions that seem to be most justified by experiment and obser- 

 vation. As far as material is concerned, it is evident that the 

 selection of what to give and what to omit is a matter of judg- 

 ment and experience upon the part of the writer, but the present 

 author is convinced that the necessary reduction in material 

 should be made by a process of elimination rather than by con- 

 densation. The latter method is suitable for the specialist with 

 his background of knowledge and experience, but it is entirely 

 unfitted for the elementary student. For the purposes of the 

 latter brief, comprehensive statements are oftentimes misleading, 

 or fail at least to make a clear impression. Those subjects that 

 are presented to him must be given with a certain degree of full- 

 ness if he is expected to obtain a serviceable conception of the 

 facts, and it follows that a treatment of the wide subject of physi- 

 ology is possible, when undertaken with this intention, only by 

 the adoption of a system of selection and elimination. 



The fundamental facts of physiology, its principles and modes 



