v ANIMAL AUTOMATISM 209 



bers which are sensitive in such a manner, that the slightest 

 touch which excites the part of one of the members to which a 

 thread is attached, gives rise to a motion of the part of the brain 

 whence it arises, just as by pulling one of the ends of a stretched 

 cord, the other end is instantaneously moved. . . . And we 

 must take care not to imagine that, in order to feel, the soul 

 needs to behold certain images sent by the objects of sense to 

 the brain, as our philosophers commonly suppose ; or, at least, 

 we must conceive these images to be something quite different 

 from what they suppose them to be. For, as all they suppose is 

 that these images ought to resemble the objects which they re- 

 present, it is impossible for them to show how they can be 

 formed by the objects received by the organs of the external 

 senses and transmitted to the brain. And they have had no 

 reason for supposing the existence of these images except this ; 

 seeing that the mind is readily excited by a picture to conceive 

 the object which is depicted, they have thought that it must be 

 excited in the same way to conceive those objects which affect 

 our senses by little pictures of them formed in the head ; instead 

 of which we ought to recollect that there are many things be- 

 sides images which may excite the mind, as, for example, signs 

 and words, which have not the least resemblance to the objects 

 which they signify." * 



Modern physiology amends Descartes' conception 

 of the mode of action of sensory nerves in 

 detail, by showing that their structure is the same 

 as that of motor nerves; and that the changes 

 which take place in them, when the sensory organs 

 with which they are connected are excited, are of 



1 Locke (Human Undcrstmiding, Book II., chap. viii. 37) 

 uses Descartes' illustration for the same purpose, and warns us 

 that " most of the ideas of sensation are no more the likeness of 

 something existing without us than the names that stand for 

 them are the likeness of our ideas, which yet, upon hearing, they 

 are apt to excite in us," a declaration which paved the way for 

 Berkeley. 



VOL. I P 



