434 DISEASES OF THE NERVOUS SYSTEM. 



Microscopically, the characteristic features are found to be 

 an increase of the neuroglia-tissue and destruction of the 

 myelin-sheaths, and later of the axis-cylinder whether the 

 nervous tissue or the neuroglia-tissue is primarily affected is 

 not known (Fig. 205). Similar changes may occur in the 

 cranial nerves, especially in the optic, and in the spinal nerves. 



The prominent clinical feature inco-ordination is due to 

 the interference with the centripetal, nerve-fibres, especially 

 those coming from the muscles. This explains also the early 

 loss of muscle-reflexes. Actual loss of muscle-power indicates 

 implication of the motor tracts in the lateral columns ; and 



FIG. 206. 



Photo-micrograph of a section of the cervical spinal cord (from a case of amyo- 

 trophic lateral sclerosis). Degeneration of the crossed pyramidal and direct 

 tracts and the antero-lateral ground-fibres. The direct cerebellar tracts, the 

 antero-lateral ascending tracts, and especially the posterior columns, are unaf- 

 fected. There was almost complete absence of cells and fine nerve-fibre retic- 

 ulum in the anterior horns; this is observable by the difference in color as 

 compared with the posterior horns (F. W. Mott). 



localized atrophies, which may aifect certain groups of muscles, 

 if not due to such paralysis, results from the extension of the 

 disease to the anterior cornua. 



Friedreich's disease, or hereditary ataxia, occurs at an early 

 age, generally in several members of the same family. Ana- 

 tomically, the characteristic features are degenerative changes 

 in the posterior and lateral columns, involving the pyramidal 

 and direct cerebellar tracts. 



Spontaneous lateral sclerosis (Erb's spastic paraplegia) is a 



