An Introduction to a Biology 



tains, booby-traps and mechanical figures of men 

 which played mock musical instruments, all supplied 

 and worked from an office in the centre of the garden, 

 from which pipes radiated to the various displays, 

 and in which sat the hireling who, by turning on 

 one tap, could turn such and such a fountain on, or 

 by turning another make a mechanical figure play a 

 fiddle. The various activities of the whole appara- 

 tus were determined by the diameter of the pipes, 

 by the way in which they were fitted into the water- 

 falls and figures, by valves in them, and by any 

 ingenuities the inventor chose to devise in them. 

 The man in the central office only had to turn the 

 right taps or levers to direct the water in the desired 

 channel, and, provided there was no leakage, and 

 the joints and wheels were well oiled, he could 

 make any part of the system perform as he wished. 

 The various parts, and the whole, of this system 

 did what it did because of the way in which it was 

 made. If the mechanical 'cello -player was served by 

 the same pipe as that which worked a neighbouring 

 fountain, he had to play when this fountain played. 

 Descartes compared the nerves (which he believed 

 to be hollow) in the human body to the pipes in 

 such a grotto, the animal spirits (which he believed 

 to be gaseous) to the water which drove the system, 

 and the muscles and limbs to the various displays. 

 The entrances of the tunnels in the nerves into the 

 brain were guarded by doors ; and when the body 

 was in a state of rest the animal spirits were pent 

 up in the cavities of the brain ; but when a stimulus 

 was received from the outside, it was transmitted 

 along a nerve to the brain, the doors guarding the 



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