PEE FAG E. 



WITH the completion of this volume, all of the subjects 

 belonging to human physiology, that are usually taught in 

 medical schools or are treated of in systematic works, have 

 been carefully considered, except the functions of the ner- 

 vous system and the processes of generation and development. 

 The first volume, published in 1866, treated of the blood, 

 circulation, and respiration ; and the second volume, pub- 

 lished in 1867, was upon the subjects of alimentation, diges- 

 tion, absorption, and the lymph and chyle. 



The original plan of the work has been adhered to in the 

 preparation of these three volumes, as each one constitutes a 

 separate and distinct treatise, being complete in itself, while 

 the full series is intended to cover the entire subject of 

 human physiology. In recording the success of the parts 

 already published, the author feels that his labors have been 

 more than appreciated; and the friendly and encouraging 

 criticism that the work has thus far received has stimulated 

 him to increased efforts in the preparation of the present 

 volume. 



Some of the subjects taken up in this volume have an 

 especial interest to the author, from the fact that he has 



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