PEEFACE. 





X the present edition I have made considerable changes and 

 ditions ; but in the changes I have tried to maintain the 

 character of the book as presented in previous editions ; and the 

 additions, with the exception of the histological paragraphs, are 

 caused not by any attempt to add new matter or to enlarge the 

 general scope of the work, but by an effort to explain more fully 

 and at greater length what seem to me to be the most funda- 

 mental and most important topics. I have been led to introduce 

 some histological statements, not with the view of in any way 

 relieving the student from the necessity of studying distinct 

 histological treatises, but in order to bring him to the physio- 

 logical problem with the histological data fresh in his mind. I 

 have therefore dealt very briefly with the several histological 

 points and confined myself to matters having a physiological 

 bearing. My friends Dr Gaskell, Mr Langley and Dr Lea have 

 given me great assistance throughout, and their names might 

 fitly appear on the title page, were it not that the present arrange- 

 ment makes me alone responsible for all shortcomings. I have 

 also to thank my senior demonstrator Mr L. E. Shore, M.B. and 

 my junior demonstrator Mr Wingfield, M.A. for much valuable 

 aid. The second and third parts will follow this first part as 

 soon as possible. 



