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I 



AUTHOR'S PEEFACE TO THE SIXTH 

 EDITION 



I HAVE taken advantage of the alteration in the size of the page and 

 of the type which Mr Murray has thought wise to adopt, to make 

 considerable changes in the present edition. I have throughout, 

 however, endeavoured to remember that the main object of the work 

 is to supply students with a complete but elementary text-book. 

 Sections which treat of what may be termed " advanced work " have 

 therefore been made as brief as possible, and have been inserted in 

 small print. The student on reading the book for the first time will 

 find it best to omit these passages. When he has mastered the 

 continuous story told in the large text, he will then be able to study 

 what is given in small type. 



During the past few years two important advanced text-books 

 have made their appearance ; one published in this country, under the 

 editorship of Professor Schafer, F.E.S., and the other in America, 

 under the editorship of Professor Howell. I am much indebted to 

 both of these for assistance in bringing this book up to date. I have 

 also to thank Professor Schafer for allowing me to copy several of 

 the instructive new diagrams which have appeared in his Essentials 

 of Histology. 



The parts of this book which have undergone most revision are 

 those relating to the nervous system and to the circulation of the 

 blood. Under the latter head I have devoted some space to those 

 elementary principles of physics which underlie what is often called 

 hsemodynamics. Experience in teaching has shown me that although 

 students may have previously received instruction in physics and 



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