242 DISEASES OF THE BRAIN. 



During the first year of life, tuberculosis of the meninges is rare ; 

 jiter, during childhood, it is proportionately frequent ; in adults, only 

 solitary cases occur, except where it complicates chronic pulmonary 

 consumption. Among the exciting causes, premature or excessive 

 mental exertion is blamed most frequently for exciting hydrocephalus 

 in children ; this is probably unjust. Children not predisposed to it 

 may be mentally stimulated to any extent without inducing hydro- 

 cephalus ; and the early development of children falling a prey to this 

 disease is due to their predisposition, not to their bringing up ; this is 

 not the cause of their hydrocephalus. The same is true of the asser- 

 tion that a blow or fall on the head induces tuberculosis of the menin- 

 ges and acute hydrocephalus. It is almost always easy to make out 

 that the sick child has, some time or other, fallen on its head ; but it 

 does not thence follow that this fall is to be regarded as the cause of 

 his disease. 



ANATOMICAL APPEARANCES. In basilar meningitis we find a yel- 

 lowish, opaque exudation, which is sometimes very plentiful, in the 

 meshes between the pia mater and arachnoid, especially about the 

 optic chiasm, as well as in the portions of the meninges extending 

 toward the pons and medulla oblongata, and thence along the larger 

 cerebral fissures, particularly the fossa of Silvius, toward the convex 

 surface of the brain. At the same time, we almost always find the 

 pia mater covered with whitish granulations, the size of a grain of 

 sand or a hemp-seed, most distinctly so in the vicinity of the blood- 

 vessels. 



In simple miliary tuberculosis of the meninges the changes are less 

 marked, and it is only on careful examination at the above places that 

 we find numerous, usually very small, whitish, granular opacities of 

 the pia mater, whose significance is often only rendered evident by the 

 coincident occurrence of hydrocephalus and the presence of tubercle 

 granulations in other organs. 



In both forms, the ventricles, especially the lateral and the third 

 ventricles, are sometimes moderately, sometimes considerably dilated 

 by serous fluid. The latter is occasionally quite clear, but is usually 

 clouded by flocculi. The walls of the ventricle, but especially of the 

 fornix and commissures, are at the same time so softened that they 

 usually break down on the slightest touch. This (hydrocephalic) soft- 

 ening spreads indefinitely, often far beyond the immediate neighbor- 

 hood of the ventricle. The larger the effusion in the ventricles, the 

 more bloodless and pale the brain becomes, and the whiter the soft- 

 ened parts. 



SYMPTOMS AND COURSE. There is no symptom pathognomonic cf 

 oasilar meningitis, and which alone will render a diagnosis possible* 



