x] of the Nervous System. 261 



constituted a fluid, a fluid very subtle indeed and of a wholly 

 peculiar nature, but still a fluid and so far amenable to the 

 physical laws governing fluids. It was in his time a doctrine 

 daily gaining ground that the nerves were tubes along which 

 the animal spirits flowed. Laying hold of this doctrine and 

 making use of some known general facts of the topography of 

 the brain and nerves, he constructs an ideal nervous machine 

 consisting of the brain as a centre and of nervous tubes radiating 

 from this centre and carrying the animal spirits to all parts 

 of the body. And, in order to make the exposition of .the 

 working of this machine clear and convincing, he does not 

 hesitate to attribute to its various parts features which he 

 describes as if they belonged to the common knowledge of 

 the time, though neither he nor anyone else had actually 

 seen them. 



His exposition of the general working of the machine is as 

 follows : 



"For you must know that the arteries which bring the 

 " blood from the heart after having divided into an infinite 

 " number of small branches and having formed the delicate 

 " tissue which is spread like a carpet over the floor of the 

 " ventricles of the brain, are gathered together round a certain 

 " little gland which is placed about the middle of the substance 

 "of the brain, just at the entrance into the ventricles. And 

 " these arteries have in this situation a large number of minute 

 " orifices through which the more subtle particles of the blood 

 "which they hold can flow into this gland but which are so 

 " narrow that they do not permit any passage through them of 

 " the grosser particles. 



" You must also know that these arteries do not end there 

 "but, being gathered together again, several into one, they 

 "ascend straight upwards and join the great vessel, which 

 " is like a Euripus, and which bathes the outer surface of the 

 " brain. And it must be noticed that the grosser particles of 

 " the blood lose a great deal of their agitation in the turns and 

 " twists of the delicate tissue through which they pass, the more 

 " so that they have the power to impinge on the smaller more 

 " subtle particles mixed with them and to transfer their move- 



