PREFACE 



FEW subjects are as well provided with text-books as physi- 

 ology ; yet it may be doubted whether the interests of the 

 amateur of science have been adequately cared for. From his 

 point of view there are certain obvious drawbacks to even the 

 most admirable of text-books. Writing for medical students, 

 their authors assume that their readers have passed through 

 two years of preliminary training in physics, chemistry, and 

 biology ; they take for granted that they will have the 

 privilege of supplementing their study of the theory of physi- 

 ology with practical work in a laboratory ; they treat all parts 

 of the subject with equal thoroughness. In this book I have 

 endeavoured to describe the phenomena of life, and the principal 

 conclusions which have been drawn as to their interdependence 

 and as to their causes, in language which will be understood by 

 persons unacquainted with the sciences upon which physiology 

 is based. I have omitted all reference to experimental methods 

 and to the technique of the science, save when a knowledge 

 of the means by which information has been obtained is 

 essential to a comprehension of its bearing. I have passed over 

 such sections of the subject as are generally considered unsuit- 

 able for ordinary discussion. And since this book neither aims 

 at being an introduction to the systematic study of physiology, 

 nor poses as an aid in the preparation for professional examina- 

 tions, I have treated with some thoroughness the more recondite 

 and the more suggestive results of recent research, and have 

 tried to indicate the trend of modern thought regarding 

 problems as yet unsolved. I have endeavoured to reflect the 



