xii PREFACE. 



both the principles, and their application to the subject of 

 physiology, would on this account have been liable to be 

 questioned. Besides which, it is an honester part to shew the 

 full extent of a doctrine, than to leave others to make their 

 own application or construction of it ; and I am the less dif- 

 fident in doing this, in the present instance, because I feel a 

 confidence that the cause which, by an ignorant or a superfi- 

 cial reader, may be supposed to be militated against by these 

 doctrines, is, to fhe extent to which they apply, in reality 

 served by them, as much as a cause can be served by placing 

 it upon a true and solid, instead of a false or fanciful ground. 

 In addition, it may be remarked that the vulgar are not likely 

 to be interested or swayed by a discussion which will not fall 

 in their way ; and which, if it did, they would not understand. 

 I would add, with respect to these preliminary chapters, that 

 they were composed as much as four years since ; and that the 

 work has been several months in the press. 



Another query might suggest itself to the reader, in peru- 

 sing the following pages. How is it, it may be asked, that 

 there is not in the whole book a single quotation, when it is so 

 much the present fashion to publish books which contain 

 little else but quotations ? This question certainly places me 

 in a very unlucky predicament. In justification of myself, 

 however, I must observe, that I did intend to have made one 

 or two quotations from Don Quixote ; but it so happens, that, 

 much as I reverence the authority of Cervantes, I had no oc- 

 casion even for these. But although this custom of quotation 

 has not in the work itself been treated with much respect, the 

 deficiency may be thus made some amends for in the preface ; 

 where, indeed, I have great occasion for a reply to those who 

 would ask why there are no quotations in my book, when 

 works of fashion, and reputed erudition, are found to have 

 three authorities, and sometimes five, at the bottom of every 

 page ? This very deficiency Cervantes himself thus patheti- 

 cally laments : " Other authors can pass upon the public, by 

 stuffing their books from Aristotle, Plato, and the whole com- 

 pany of ancient philosophers; thus amusing their readers into 



