EXTRACT III. 



ON THE CHOROID PLEXUSES, AND PIA MATER GENE- 

 RALLY, AS THE SECRETIVE ORGANS OF THE 

 CEREBRO-SPINAL FLUID. 



OUR attention having been for a long time given to tracing 

 and describing the neural lymph and its circulation in, and 

 throughout, the central and peripheral nervous system, and 

 working out the role played by that circulation, in ordinary 

 physiological conditions as well as in the genesis, progress, 

 and results of the diseases to which that system is liable, 

 we have often been struck with the thought that such a 

 circulation, embracing as it does the whole neural lymph 

 production and disposal throughout the entire areas 

 embraced by that system, must necessarily to use a bull 

 be derived from somewhere specifically, or from a propor- 

 tionately large extent, or number, of secreting agencies or 

 structures. Of these agencies we are satisfied that the 

 principal is the general vascular mechanism of the pia 

 mater, which virtually surrounds the whole central nervous 

 textures of brain and cord, and secretes, or excretes, into 

 the surrounding and overlying inter-spaces of that system 

 the proper amount of fluid, when and where required. 

 This may, speaking generally, be regarded as fully 

 meeting the requirements of the external aspects and 

 inter-spaces of the structures filling the cerebro-spinal 

 cavity, and only very indirectly, and with difficulty, the 

 central intra-spaces and cavities of these structures ; there- 

 fore, it would seem to us to require supplementing by 

 other and internal, or intra-cerebral means, to meet directly 

 the requirements of the intra-cerebral and intra-spinal 



