V ANIMAL AUTOMATISM 217 



exposition of physics, I can say no more on this subject than I 

 have already said in the fifth part of my Treatise on Method : 

 yet, I will further state, here, that it appears to me to IH> :i very 

 remarkable circumstance that no movement can take place, 

 either in the bodies of beasts, or even in our own, if these 

 bodies have not in themselves all the organs and instruments 

 by means of which the very same movements would be accom- 

 plished in a machine. So that, even in us, the spirit, or the 

 soul, does not directly move the limbs, but only determines the 

 course of that very subtle liquid which is called the animal 

 spirits, which, running continually from the heart by the brain 

 into the muscles, is the cause of all the movements of our limbs, 

 and often may cause many different motions, one as easily as the 

 other. 



"And it does not even always exert this determination ; for 

 among the movements which take place in us, there are many 

 which do not depend on the mind at all, such as the beating of 

 the heart, the digestion of food, the nutrition, the respiration 

 of those who sleep ; and even in those who are awake, walking, 

 singing, and other similar actions, when they are performed 

 without the mind thinking about them. And, when one who 

 falls from a height throws his hands forward to save his head, 

 it is in virtue of no ratiocination that he performs this action ; 

 it does not depend upon his mind, but takes place merely 

 because his senses being affected by the present danger, some 

 change arises in his brain which determines the animal spirits 

 to pass thence into the nerves, in such a manner as is required 

 to produce this motion, in the same way as in a machine, and 

 without the mind being able to hinder it. Now since we observe 

 this in ourselves, why should we be so much astonished if the 

 light reflected from the body of a wolf into the eye of a sheep 

 has the same force to excite in it the motion of flight ? 



" After having observed this, if we wish to learn by reasoning, 

 whether certain movements of beasts arc comparable to those 

 which are effected in us by the operation of the mind, or, on the 

 contrary, to those which depend only on the animal spirits and 

 the disposition of the organs, it is necessary to consider the 

 difference between the two, which I have explained in the fifth 

 part of the Discourse on Method (for I do not think that any 



