PEEFAOE. 



THE present edition of this treatise has been rewritten ; and while the 

 general arrangement of subjects is retained, but little remains of the 

 original text. Although the third edition, published in 1880, is still 

 much used as a text-book, for several years I have not been able to follow 

 it closely in public teaching ; and its defects have become so important 

 that it has seemed to me impossible to remedy them without making a 

 new book. 



I have thought it advisable to curtail still more the historical refer- 

 ences contained in former editions. At the present day it is not possible 

 to give even a brief account of the literature of physiology within the 

 limits of a single volume of convenient size. I have avoided, also, as far 

 as practicable, discussions of unsettled and disputed questions, as un- 

 profitable and confusing. 



I have adopted the new, chemical nomenclature, which is now almost 

 universally accepted, but have not attempted to give a full account of the 

 chemistry of the body. Physiological chemistry has now become a sci- 

 ence by itself ; and while it has contributed very largely to exact, physio- 

 logical knowledge, its full consideration is properly confined to special 

 treatises. 



Eecent advances in the knowledge of minute anatomy, due largely to 

 improved instruments and methods, have had an important share in the 

 progress of physiology. These have been considered incidentally, and 

 they now form an essential part of all complete works on anatomy. 



One who has long been a student and teacher of physiology can 

 hardly fail to have an idea, more or less definite, of what a text-book 

 should be, however imperfectly he may carry out this idea in his own 

 work. I shall be more than satisfied if I have been able to give concise 

 and connected statements of well-established facts, in such a form that 

 they can easily be acquired by students and in language that can not be 

 misunderstood. Peculiar views and theories, whether of the author or of 

 others, have no proper place in a text-book, which should represent facts 

 generally recognized and accepted, and not the ideas of any one individual 



