CHAPTER XI. 

 DISEASES OF THE NEEVOUS SYSTEM. 



THE BRAIN AND ITS MEMBRANES. 

 MENINGITIS. 



Suppurative meningitis may be local or diffuse. The common 

 form is a diffuse leptomeningitis involving the base or the 

 convexity of the brain or even the whole area of the subarachnoid 

 space. The wide extent and loose meshwork of this space 

 especially favour the diffusion of the suppurative process. On 

 the convexity of the brain the pus at first lies in the sulci where 

 the spaces between pia and arachnoid are larger than over the 

 convolutions. 



The meningitis is always associated with encephalitis because 

 the lymphatic sheaths of the pial vessels carry the infection to 

 the superficial layers of the brain substance. The interior of 

 the brain may also be invaded by extension along the pia and 

 arachnoid where they become invaginated into the cerebral 

 ventricles at the great transverse fissure. 



The infection of the meninges may be direct or through the 

 medium of arteries, veins, or lymphatics. 



Direct infection is the result of open fractures of the vault of 

 the skull, of perforating wounds or of basal fractures which 

 involve the cavities of the nose, the naso-pharynx or the ear. 

 Infection through the medium of the arterial stream occurs in 

 certain general infective diseases of which pneumonia may be 

 taken as an example, and also in pyaemia. The emissary and 

 some of the diploic veins of the skull may carry suppurative 

 organisms to the sinuses and so to the membranes. In some 

 cases the lymphatic sheaths surrounding the arteries which enter 



