332 LAY SERMONS, ADDRESSES, AND REVIEWS. [xiv. 



"Discourse," and erroneously describing the motion of 

 the blood, not to the contraction of the walls of the 

 heart, but to the heat which he supposes to be generated 

 there, he adds : — 



"This motion, which I have just explained, is as much the necessary 

 result of the structure of the parts which one can see in the heart, and 

 of the heat which one may feel there with one's fingers, and of the 

 nature of the blood, which may be experimentally ascertained ; as is 

 that of a clock of the force, the situation, and the figure, of its weight 

 and of its wheels." 



But if this apparently vital operation were explicable 

 as a simple mechanism, might not other vital operations 

 be reducible to the same category? Descartes replies 

 without hesitation in the affirmative. 



"The animal spirits," says he, "resemble a very subtle fluid, or a 

 very pure and vivid flame, and are continually generated in the heart, 

 and ascend to the brain as to a sort of reservoir. Hence they pass 

 into the nerves and are distributed to the muscles, causing contraction, 

 or relaxation, according to their quantity." 



Thus, according to Descartes, the animal body is an 

 automaton, which is competent to perform all the animal 

 functions in exactly the same way as a clock or any other 

 piece of mechanism. As he puts the case himself : — 



" In proportion as these spirits [the animal spirits] enter the cavities 

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

 these pores into the nerves ; where, according as they enter, or even 

 only tend to enter, more or less, into one than into another, they have 

 the power of altering the figure of the muscles into which the nerves 

 are inserted, and by this means of causing all the limbs to move. 

 Thus, as you may have seen in the grottoes and the fountains in royal 

 gardens, the force with which the water issues from its reservoir is 

 sufficient to move various machines, and even to make them play 

 instruments, or pronounce words according to the different disposition 

 of the pipes which lead the water. 



"And, in truth, the nerves of the machine which I am describing may 

 very well be compared to the pipes of these waterworks ; its muscles 

 and its tendons to the other various engines and springs which seem to 

 move them ; its- animal spirits to the water which impels them, of 

 which the heart is the fountain ; while the cavities of the brain are 



