830 THE NERVOUS SYSTEM. 



The areas of sclerosis may involve both gray and white matter, and 

 may be very small or large (Fig. 543). If very small or in early stages 

 of formation, they may not be recognizable by the naked eye, bnt when 

 visible they are grayish, translucent, and firmer than the surrounding 

 tissue, and may or may not present a depressed surface ; they sometimes 

 project above the general level. The cause of this as of all other forms 

 of so-called idiopathic interstitial myelitis is very obscure. As noted in 

 multiple sclerosis in the brain, secondary degenerations are rare, and 

 probably for the reason there given. 



Chronic Interstitial Neuritis. This is essentially a chronic interstitial 

 inflammation resulting in an increase of the connective tissue in the nerve 

 sheaths and intrafascicular bands. As a result of this the nerve fibres 

 undergo atrophy from pressure ; the medullary sheaths and finally the 

 axis cylinders being in many of the fibres partially or completely de- 

 stroyed. 



Tic Douloureux. Changes in the peripheral branches of the fifth 

 cranial nerve removed from obstinate cases of trifacial neuralgia have 

 been reported in a considerable number of cases. These changes consist 

 in degeneration of the axis cylinders and of their medullary sheaths. In 

 a smaller number of instances changes have been reported in Gasserian 

 ganglia removed from such cases. The changes in the ganglia consist in 

 atrophy and disappearance of the nerve cells with increase in the con- 

 nective-tissue elements. A peculiar shrunken condition of the cell in 

 which the cell retracts to one side of its cell space is a fairly character- 

 istic feature. 



TUBERCULOUS LESIONS IN THE NERVOUS SYSTEM. 



Tuberculous inflammation whether of the brain or cord is usually sec- 

 ondary to tuberculous inflammation in other organs, and is most fre- 

 quent as an extension of tuberculosis of the meninges. In the brain sub- 

 stance it usually manifests itself in the formation of circumscribed masses 

 of new tissue from 0.5 to 1 cm. in diameter, or larger. These may be 

 single or multiple, are most common in young persons, and very fre- 

 quently occur in the cerebellum (Fig. 544). They are apt to occur in 

 connection with tuberculous inflammation of other organs. They are 

 frequently called solitary tubercles, and usually consist of a dense cen- 

 tral cheesy mass, around which is a grayish zone containing tubercle 

 granula, numerous small spheroidal cells, with occasionally larger poly- 

 hedral cells and giant cells. They do not, as a rule, seem to be formed 

 by an aggregation of miliary tubercles, although these may be present 

 in the periphery. They sometimes suppurate and break down, and then 

 they simulate simple abscesses. Tubercle bacilli have been found in 

 these solitary tubercles. 



Conglomerate and scattered miliary tubercles of the ordinary form 



