PREFACE 



THE FOUKTH EDITION 



The general arrangement and plan of this book remain the same 

 as in previous editions. The subject matter has been brought up 

 to date. 



I have endeavoured to keep the work within a moderate 

 compass, but, with the advance of the science, even its essentials 

 expand. 



The principal additions now introduced are new sections 

 relating to the chemistry of nervous tissues and of the purine 

 compounds and to the important subject of osmosis. The 

 description of the phenomena of polarised light has also been 

 considerably expanded. 



I have to thank Dr. H. Willoughby Lyle, who has again 

 assisted me in reading proof-sheets and preparing the Index. 



W. D. HALLIBUKTON. 



King's College : May 1901. 



