262 The Older Doctrines [lect. 



" ment to these. But these more delicate particles are not able 

 "in the same way to lose their movement, which indeed is 

 "increased by the movement transferred to them from the 

 "grosser particles, since there are no other bodies in their 

 "neighbourhood to which the latter can so easily transfer their 

 " movement. 



"Hence it will be easily understood that these grosser 

 " particles, as they ascend straight up towards the outer surface 

 " of the brain where they serve for the nutrition of its substance, 

 "bring it about that the more delicate and more agitated 

 " particles are turned aside, and all enter into this gland, which 

 " must be regarded as a very full reservoir whence the spirits at 

 "the same time flow into the ventricles of the brain. Thus, 

 " without any other preparation or change except that they are 

 " separated from the grosser particles and that they still retain 

 "the extreme velocity which the heat of the heart has given 

 " them, they cease to have the form of blood and are called 

 " animal spirits. 



" Now as these spirits enter thus into the ventricles of the 

 "brain, so they pass thence into the pores of its substance and 

 " from these pores into the nerves. And according as they 

 " enter or even only as they tend to enter more or less into 

 " this or that nerve they have the power of changing the form 

 " of the muscle into which the nerve is inserted and by this 

 " means of making the limbs move. You may have seen in the 

 " grottoes and fountains which are in our royal gardens that 

 " the simple force with which the water moves in issuing from 

 "its source is sufficient to put into motion various machines 

 " and even to set various instruments playing or to make them 

 " pronounce words according to the varied disposition of the 

 "tubes which convey the water. 



" And indeed one may very well compare the nerves of the 

 " machine which I am describing with the tubes of the machines 

 " of these fountains, the muscles and tendons of the machine 

 " with the other various engines and springs which serve to 

 "move these machines, and the animal spirits, the source of 

 " which is the heart and of which the ventricles of the brain 

 " are the reservoirs, with the water which puts them in motion. 



