PREFACE 



THIS book consists of four lectures which 

 were delivered in the Physiological Labora 

 tory of Guy's Hospital, during May of this 

 year, as a London University course for 

 senior students. They are reproduced in the 

 form of their delivery, after careful revision, 

 in which I have been much aided by the 

 criticisms and suggestions of my friend 

 Professor J. T. Wilson, F.R.S. 



Philosophical readers who may have chanced 

 to see an essay by my brother and myself on 

 ' The Relations of Philosophy to Science ' in 

 Essays in Philosophical Criticism, published in 

 1883, will recognise in these lectures a de 

 velopment of the ideas put forward in that 

 essay. In a presidential address which I 

 delivered in 1908 before the Physiological 

 Section of the British Association, and in 

 other scattered papers, the same line of argu 

 ment in relation to the aims of biology and 



