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THE NERVOUS SYSTEM. 



Tuberculous Meningitis. This is especially characterized by the forma- 

 tion in the pia mater of miliary tubercles, associated with more or less 

 well-marked exudative inflammation. It may occur in adults and in 

 children, but is more common in the latter. The dura mater may be 

 unchanged, or its inner surface may be sprinkled with miliary tubercles. 

 The pia mater may or may not be congested ; it may look dry on the sur- 

 face or it may be oedematous. Usually the brain seems to fill the cere- 

 bral cavity to an unusual degree, and the convolutions are flattened. If 

 the pia mater be redematous the serum may be clear, or turbid with pus 

 and fibrin. The membrane may present any of the general appearances 

 of exudative meningitis. But always in addition to these, and sometimes 

 without them, are found miliary tubercles. These may be few and widely 

 scattered, or present in great numbers. They are most numerous along 

 the blood-vessels, but may occur anywhere. They are usually abundant 

 at the base of the brain. On the convexity they are most common along 

 the surfaces of the sulci. " Some of the tubercles are so small as to be 

 scarcely visible or entirely invisible to the naked eye ; others are as large 

 as a pin's head or larger. They may be formed in the membranous 



FIG. 507. MILIARY TUBERCLE OF THE PIA MATER OF A CHILD. 



an area of caseation at the centre ; on the right of this are two giant cells : there is a peripheral 

 zone of small cells. The leucocytes are increased in the meshes of the pia. 



prolongations of the pia mater which dip into the sulci, around the ves- 

 sels which enter the brain substance, in the choroid plexus and ependyma 

 of the ventricles, and may exist in the spinal cord. 



The miliary tubercles have the usual structural characters of focal 

 tuberculosis in connective tissue (Fig. 507). 



In children the ventricles are usually more or less distended by an 

 accumulation of transparent or turbid serum, and the walls of the ven- 

 tricles may be studded with miliary tubercles (see Fig. 508). In adults 

 the ventricles are less frequently involved. The brain tissue around 

 the ventricles is often softened. The central canal of the spinal cord 

 may also be dilated. It is the dilatation of the ventricles which causes 

 the flattening of the convolutions, and the flattening is usually in direct 

 proportion to the amount of accumulated fluid. 



Owing to the frequency of the dilatation of the ventricles with serum 

 in children, the disease is often called acute hydrocephalus. 



In both children and adults the tuberculous inflammation may produce 

 large masses of tuberculous tissue, which undergo cheesy degeneration, 

 and may involve the brain tissue. 



