THE MECHANISTIC CONCEPTION OF LIFE 153 



mined by valves, some of whicli are placed in the heart itself, 

 others at the place of origin of the great arteries and veins, and 

 others, again, in the veins and lymphatics. The velocity with 

 which they stream through the vessels depends upon the propul- 

 sive power of the heart, upon the varying calibre of the arteries 

 and veins, and upon the posture of the body, for it is apparent 

 that more power is expended upon circulating the blood when 

 a man stands erect than when he sits down or reclines. 



So far, then, the bodily apparatus is a purely mechanical one — 

 levers of various shapes and " orders," elastic parts that pull 

 these levers, and channels along which fluids are propelled by the 

 action of a force pump and are directed by means of valves. It 

 would be possible to construct a model of the human body which 

 would carry out the same kinds of motions that are made by 

 the living organism. We should have to supply to this model 

 some source of hydraulic power, some automatic contractile 

 vessel worked by a spring that would cause the fluids to circu- 

 late in the vessels, and we should have to devise some 

 means of supplying motive force to the muscles — say, compressed 

 air from a reservoir contained somewhere in the body itself. 

 There might be springs here and there on the surface of the 

 model, and these could be made to actuate valves in the reservoir 

 of compressed air, so that by touching them the limbs of the 

 model would perform certain motions. All this is quite possible, 

 and, indeed, automata of such a kind have been constructed. 

 It would, of course, be impossible to imitate the extreme minute- 

 ness of some parts of the animal body, or to duplicate the 

 intricacies of the motions of other parts, but such limitations 

 would be due only to our defective craftsmanship. There would, 

 of course, be an essential and very curious difference between the 

 activities of the living animal and those of the mechanical 

 model — a difference which is rather hard to describe in simple 

 language. 



The Cartesian Mechanism. — Descartes thought about the 

 animal body as just such a mechanism as that suggested above. 

 The bodies of the lower animals were pure automata, so that if 

 they were touched, or pinched, or otherwise stimulated (as we 

 should say), they would move, or fight, or run away, or cry out, 

 etc., but these responses were as mechanical as would be the 

 movements made by the model when a spring was pressed. The 

 body of a man, he said, was also an automaton, but it contained 



