EXTRACT VI. B. 



ON DISEASED CONDITIONS, ARISING FROM MECHANICAL 

 INTERFERENCE WITH THE INTEGRITY OF THE 

 INTER-MENINGEAL AND INTRA-CEREBRO-SPINAL 

 SPACES. 



Ix the normal condition of these inter- and intra- spaces a 

 continuity of lumen is maintained, by which the gross 

 quantity of cerebro-spinal fluid is secured and maintained 

 in proportion suitable for the internal support and external 

 protection of the central nervous structures, and for keep- 

 ing open a means whereby its circulation is secured from 

 end to end of the brain and cord ; and that the quantity 

 of fluid can be increased and diminished indicates the 

 existence of means of escape and of entrance to the canal ; 

 but as we have elsewhere described these means, we merely 

 recall that a choice of exits is provided, whereby local and 

 general intra-pressure can be lessened and also increased, 

 according to the exigencies of intra- and extra-cerebro- 

 spinal hydrostatics. 



In certain pathological conditions, these facilities for the 

 equalisation of intra-cerebro-spinal pressure become non- 

 operative, and such untoward diseases arise in consequence 

 as acephalism, hydro-cephalism the former during foetal 

 life, the latter also then, but more especially in early post- 

 natal life hydro-myelia and syringo-myelia the last- 

 mentioned usually in adult or advanced life. 



Acephalism usually arises from preceding hydro- 

 cephalic conditions, rupture of the surrounding, or cor- 

 tical, and non-nervine cephalic structures, and escape of 

 contents, with shrinkage of the brain substance, but does 

 not necessarily interfere with the growth of the body ; 



