36 1 INTRODUCTION. 



so pure and so unmixed, that the nervous system, — the imme- 

 diate instrument of the mind, — has no part in them ; and 

 consequently it is necessary that the structure and functions 

 of the nervous system should be well understood by those who 

 would determine what should be ascribed in animal actions to 

 the operations and structure of the nervous system, and what 

 should be clearly assigned to the immaterial soul alone. 



After all the earnest attempts of the greatest philosophers 

 and physicians from the earliest ages, to explain the functions 

 of the nervous system, we can hitherto only say with Haller,^ 

 it is but a little that we certainly know, that much remains 

 unknown, and if we may judge of the future by the past, that 

 no httle will remain unknown for ever. Nevertheless, I do 

 not think all hope should be abandoned, especially if we should 

 be able to detect and remove the cause of that slow progress 

 hitherto made ; and this, in my opinion, partly consists in the 

 difficulties of the subject, which nothing but great labour can 

 overcome; and partly in the love of hypotheses, which 

 have been devised to explain the functions of the nervous 

 system. Many, content with these false resemblances of truth, 

 neglect to inquire into the truth itself, and they who do inves- 

 tigate, unless they discard the prejudices which spring from 

 hypothesis, often fail to perceive the truth, even when it is 

 plain before them. 



I have therefore entered on this attempt, to explain the 

 natural functions of the nervous system, without any hypothesis, 

 and by simple facts only; and should the attempt be approved, 

 and by additions and emendations be rendered more complete 

 (and these I well know my labours to stand in need of), it 

 may be readily and usefully applied to an explanation of the pre- 

 ternatural functions of the same system. I have taken certain 

 observations and experiments of celebrated men as a founda- 

 tion ; I have spoken doubtfully of what was doubtful, and I 

 have preferred to acknowledge my ignorance of what was inex- 

 plicable, rather than with the itch of explaining everything to 

 have recourse to improbable hypotheses. How nearly I have 

 attained to the truth in other respects let the indulgent reader 

 decide. 



' Elem. Physiol., torn, v, p. 529. 



