PREFACE TO THE SECOND EDITION xi 



far as these were errors of fact, I have endeavoured to correct 

 them ; so far as the points raised were based upon differences in 

 conception, or points of view, I have conscientiously tried to allow 

 them their full value. Translations of the book into English and 

 Italian are in course of preparation, and a Russian edition 

 has recently appeared. Since the latter was published wholly 

 without my knowledge, and has not been seen by either my 

 publisher or myself, I am forced to disclaim all responsibility for 

 it. 



I cannot forbear expressing my warmest thanks to Dr. Gustav 

 Fischer, for the pains taken by him in issuing the present edition. 



THE AUTHOR. 



UNIVERSITY OF JENA : 



THE PHYSIOLOGICAL INSTITUTE, 

 June, 1897. 



