THE NERVOUS SYSTEM 313 



feeling is produced and which is rightly regarded as the most astonish- 

 ing and difficult to conceive, I shall endeavour to describe the 

 mechanism in Chapter III. I shaU then do the same for the fourth 

 function of the nervous system by which it produces ideas, thoughts 

 etc., a function still more extraordinary than that which gives rise 

 to feeling. 



Since, however, I do not wish to set forth in this work anything 

 that is not based on adequate facts or observations, I shall first 

 consider the nervous fluid, and show that, so far from being a product 

 of imagination, this fluid is made manifest by effects which cannot 

 be otherwise produced, and which leave not the sUghtest doubt as to 

 its existence. 



