INTRODUCTION. XVli 



and the impulse they have given to experimental 

 physiology. 



It is not improbable that we shall continue to 

 labour in the study of the nervous system long 

 and patiently before we shall be capable of un- 

 derstanding satisfactorily its functions. Much 

 has already been said and accomplished to dissi- 

 pate the obscurities which hang over the phe- 

 nomena it developes, but, at present, we possess 

 only an outline of its important offices. 



When physiologists knew less than they do 

 at present, the production of animal heat was as- 

 cribed to chemical changes in the lungs, as it was 

 observed that similar changes, occurring without 

 the system, are accompanied by a disengagement 

 of caloric ; but since particular attention has been 

 paid to the nervous system, others have advan- 

 ced a variety of opinions and experiments, in- 

 tended to prove that animal heat is a secretion, 

 or that this system is intimately connected with 

 its production. The former opinion has been 

 promulgated and supported by WILSON PHILIP 

 with ingenuity; and the latter, in our own 

 country, has been fully developed by BRODIE, 

 with considerable diffidence and judgment. The 



