PREFACE TO THE SECOND EDITION. 



Ix presenting a new edition of this work, the author desires to 

 express his sincere acknowledgments to his professional brethren 

 for the very favorable manner in which it was received at the 

 time of its first appearance, two years ago. In the present edition, 

 the author has endeavored to supply, as fully as possible, the 

 deficiencies which, he is well aware, existed in the former volume. 

 Some of these deficiencies were evident to his own mind, while 

 others were indicated by the suggestions of judicious criticism. 

 These suggestions, accordingly, have been adopted in all cases in 

 which they appear to be well founded, and not inconsistent with 

 the general plan of the work. In those instances, on the other 

 hand, in which the views of the author on physiological questions 

 seemed to him to be positively sustained by the results of observa- 

 tion, he has retained these views unchanged in the present edition. 

 At the same time, he has abstained, as before, from the lengthened 

 discussion of theoretical points, and has purposely avoided even 

 the enumeration of new experiments and observations, wherever 

 they have not materially affected the position of physiological 

 doctrines; for in a work like the present, it is not the object of 

 the writer to give a detailed history of physiological science, but 

 only such prominent and essential points in its development as 

 will enable the reader fully to comprehend its actual condition at 

 the present time. 



The principal additions and alterations which have thus been 

 found advisable are: 



First, the introduction of an entire chapter devoted to the con- 

 sideration of the Special Senses, which were only incidentally treated 

 of in the former edition. 



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