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original sketch of his De Homine et de Fcetu was sketched out in 

 1633-34, although the work itself appeared in 1662. Such experi- 

 ments however as he made, in connection with physiology, were made 

 to verify an hypothesis which he had already formed, a method, of 

 course, exactly the reverse of Harvey, and of the new Physics. 

 Everything but his " rational soul " could be explained by his 

 hypothesis of matter endowed with extension and mobility. 



In De Homine Liber (1662) and his Formation of the 

 Foetus he developed his celebrated theory of man as an automaton. 

 We have already referred in general terms to Descartes' views. 

 He accepted Harvey's view of the circulation of the blood, but 

 erroneously ascribed its cause to the heat generated in the heart. 



"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." 



" As to the motion of the heart, he [Harvey] has said nothing not found in other 

 books, and I do not approve of it ; but as to the circulation of the blood, there he has 

 his triumph and the honour of first discovering it, for which medicine owes him much." 

 (Letter IX., 360.) 



His view of man as an automaton is set forth in the following 

 passages : 



" The animal spirits resemble a very subtle fluid, or rather a very pure and lively 

 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." 



" In proportion as 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 this or that nerve, 

 they have the power of changing the shape of the muscles into which the nerves are 

 inserted, and by this means making all the limbs move. Thus, as you may have seen in 

 the grottoes and fountains in our gardens, the force with which the water issues from its 

 reservoir is sufficient to put into motion various machines, and even to make them play 

 several instruments, or pronounce words, according to the varied disposition of the tubes 

 which conduct the water. Indeed, the nerves of the machine may very well be compared 

 with the tubes of these waterworks ; its muscles and tendons with the other various 

 engines and springs which seem to move these machines ; its animal spirits to the water 

 which impels them, of which the heart is the source or fountain ; while the cavities of 

 the brain are the central reservoir. Moreover, breathing and other like acts which are as 

 natural and usual to the body or machine, and which depend on the flow of the spirits, 

 are like the movements of a clock, or of a mill, which may be kept going by the ordinary 

 flow of water. External objects which, by their mere presence, act upon the organs of 

 sense ; and which, by this means, determine the machine to move in many different ways, 

 according as the parts of the brain of the machine are arranged, may be compared to 

 the strangers who, entering into one of the grottoes of these waterworks, unconsciously 

 themselves cause the movements which they witness. For they cannot enter without 

 treading upon certain planks which are so disposed that, if they approach a bathing 

 Diana, they cause her to hide among the reeds ; and if they attempt to follow her, they 



