CIRCULATION OF THE NERVE SPIRIT. 59 



brain is exposed, it is seen to subside during inspiration. This is 

 the second movement observed, or the effect upon the brain of the 

 respiratory pulse. But neither is this a cerebral force, but a phy- 

 sical subsidence, just as the corresponding rise is merely physi- 

 cal, and results from the act of expiration, which retarding the re- 

 turn of blood to the chest, forces up the brain upon this fluid 

 cushion. This, however, is to be noticed, that when the blood 

 leaves the skull during inspiration, it creates a vacant space which 

 has a function, or which is not vacant in point of use : in short, it 

 leaves room for the brain to expand. And if its real expansion be 

 less in volume than its apparent subsidence, then the brain may be 

 automatically rising at the moment when it is physically falling, 

 in which case the latter movement will mask the former. When 

 the lungs expand, then, there is room for the brain also to expand, 

 and when the lungs contract, there is a physical reason why the 

 brain also must contract. 



"We do not know that experience has gone further hitherto than 

 to show the possibility of the movement of the brain, in showing 

 that it has room or liberty to move. And indeed, if we consider the 

 problem, we shall perhaps find reason to think that this motion, like 

 the motions of other bodies from which we cannot separate ourselves, 

 but with which we ourselves move, must come as a theory whose 

 main case will lie in explaining all the facts. 



Yet further as to the possibility of the movement, one of the 

 most important truths of physiology lies in the insulation of the 

 different systems that make up the body. In point of function, indeed, 

 we have seen that the nervous system itself consists of individual 

 pieces, which can act either separately or in combination. But in 

 structure the whole nervous system is isolated from the rest of the 

 body, though plunged or let down into it as into a well of flesh. 

 The nerves end in loops or otherwise, but are not solidly continuous 

 with the other tissues. In short, the nervous body floats in the 

 fleshly body as the central yelk of the microcosm. We may liken 

 it to a sword of lightning in an elastic scabbard, which scabbard is 

 perpetually elongating and gathering itself up, but is always full of 

 the subtle and separate fire. Movement is compatible with this state, 

 nay, is perpetually stimulated by it where the whole subject is mov- 



