422 



DISEASES OF THE NERVOUS SYSTEM. 



In some cases the macroscopieal changes are not marked, 

 consisting simply of congestion, loss of normal lustre, and 

 slight oedema. In more severe cases the exudate, which may 

 be serous, sero-purulent, or purulent, becomes more marked, 

 and even distends the subarachnoidal space, the cerebral con- 

 volutions being flattened and the brain compressed to such 

 an extent as to give rise to coma. The ventricles may be like- 

 wise distended (Fig. 193). In some cases the exudate pre- 



FIG. 194. 



Fibrinous leptomeningitis. a, cerebral cortex ; 6, serum, with detritus, separating 

 the brain from the pia mater ; c, bloodvessel of the pia mater, the walls of whicn 

 are infiltrated with emigrating leukocytes ; d, fibrinous exudate ; e, smaller ves- 

 sel of the pia (Dunham). 



sents as an extensive, thick, opaque, fibrinous deposit on the 

 under surface of the arachnoid. In other instances a green- 

 ish-yellow, purulent exudate may cover the surface of the 

 brain to such an extent as to conceal almost entirely the con- 

 volutions of the cortex (Figs. 194 and 195). The inflamma- 



