X 



PEEFACE. 



ferences to be drawn in support of it, from the nature 

 and attributes of tbe bud^ seem to him so unassailable 

 and so convincing^ that^ although he does not ima- 

 gine thatj in the exposition here given of them, he 

 shall succeed in carrying conviction to the mind of 

 every one of his readers, he is not without a confident 

 expectation, that among all classes of these, both the 

 learned and the unlearned, the contents will greatly 

 out-number the non-contents. 



Although continually spoken of in these Letters as 

 his own theory, the author begs to disclaim all pre- 

 tensions on the score of originality. He has advanced 

 nothing that was not known or held before. The 

 only merit he is disposed to claim in connexion with 

 it is, that of having unfolded it more systematically, 

 and in greater detail, than any of his predecessors. 

 At the same time, he thinks it due to himself to state, 

 that it was worked out by him, substantially as it 

 now appears, without any assistance from others ; that 

 it was embodied in the course of Lectures on Physio- 

 logy, which he delivered in Marischal College during 

 the winter session of 1844, without any recollection 



