PEEF ACE. 



THERE is, probably, no subject connected with human 

 physiology, which has engaged the attention of experi- 

 mentalists and philosophic writers so much as the ner- 

 vous system, especially within the last few years. The 

 author has, from the first, looked upon this division of 

 the work as the most important and the most difficult of 

 all, and feels that this volume will be regarded with more 

 critical interest than any one of the series ; and if he has 

 succeeded, even in a measure, in giving, in it, a satisfac- 

 tory representation of our present positive knowledge, no 

 apology is necessary for the length of time occupied in 

 its preparation. For two and a half years, he has been 

 almost unremittingly engaged in writing this volume, and 

 has endeavored to overcome, rather than avoid, the diffi- 

 culties which have presented themselves in the investiga- 

 tion of important questions, which are as yet regarded by 

 many as unsettled. 



A great part of the inevitable delay which has attend- 

 ed the publication of this part of the work has been due 

 to the difficulty in this country of consulting rare and im- 

 portant memoirs. "When it is stated that every citation 



