x] of the Nervous System. 263 



" Moreover breathing and other like acts which are natural and 

 " usual to the machine and which depend on the flow of the 

 " spirits are like the movements of a clock or of a mill which 

 " the ordinary flow of water can keep going continually. Ex- 

 ternal objects, which by their mere presence act upon the 

 "organs of sense of the machine and which by this means 

 " determine it to move in several different ways according as 

 " the parts of the machine's brain are disposed, may be compared 

 " to strangers, who entering into one of the grottoes containing 

 " many fountains, themselves cause, without knowing it, the 

 " movements which they witness. For in entering they 

 "necessarily tread on certain tiles or plates, which are so 

 "disposed that if they approach a bathing Diana, they cause 

 " her to hide in the rosebushes, and if they try to follow her, 

 " they cause a Neptune to come forward to meet them threat- 

 ening them with his trident. Or if they pass in another 

 "direction they occasion the springing forward of a marine 

 " monster who spouts water into their faces, or things of a 

 "like kind according to the caprice of the engineers who 

 "constructed them. 



" Lastly, when the rational soul resides in this machine, it 

 " has its principal seat in the brain and may be compared to 

 " the fountaineer who has to take his place in the reservoir 

 "whence all the various tubes of these machines proceed 

 "whenever he wishes to set them going, to stop them or in 

 "any way to change them." 



Thus the pineal gland, "the little gland in the middle of 

 the substance of the brain," is the primary reservoir, and the 

 ventricles of the brain form a secondary reservoir of the animal 

 spirits, which flowing from the brain along the tubular nerves 

 carry out the movements of the body, the energy of these 

 spirits being supplied by the innate heat of the heart. He 

 explains in the following manner the particular way in which 

 the working of this nervous machine is determined by the 

 impressions of external objects. The nerves are not mere 

 hollow tubes, provided with valvular arrangements by means of 

 which the flow of the animal spirits outwards from the brain to 

 the muscles and other structures is regulated; they contain 



