436 DISEASES OF THE NEEVOVS SYSTEM. 



probably, in most cases, both the direct and crossed pyramidal 

 tracts are involved. In some instances the pyramidal tracts 

 in parts of their course may be affected before the anterior 

 cornua, which could account for the spasmodic rigidity in 

 localized muscle-groups sometimes seen. Generally, however, 

 there is no clinical evidence of the involvement of the pyram- 

 idal tracts. 



INFLAMMATION. 



Under the term myelitis inflammation of the cord is in- 

 cluded, according to different authors, a great variety of 

 affections. By many the primary degenerations just briefly 

 described are included under this heading. To those cases in 

 which the changes are limited in their longitudinal extent the 

 term transverse myelitis has been applied, in contradistinction 

 to others in which a considerable length of the cord is involved : 

 to which the term poliomyelitis (TTO^OC gray) has been ap- 

 plied when the changes are confined to the gray matter alone ; 

 or leukomyelitis (huxb$ white), when confined to the white 

 matter. 



Acute transverse myelitis, resulting in softening of the cord 

 and characterized clinically by paralysis of motion and sensa- 

 tion below the site of the lesion, may arise without assignable 

 cause. It may be due to trauma, exposure to cold, or excessive 

 venery, and certain of the acute infectious diseases have been 

 regarded as exciting causes. 



According to the color of the involved area, several stages 

 are described as red and yellow softening, and gray degener- 

 ation. 



At the first stage the tissue is pink from the engorgement of 

 the bloodvessels, and minute hemorrhages here and there. 



Microscopically, the bloodvessels are dilated and surrounded 

 by migrated leukocytes, the neuroglia-tissue is swollen and its 

 cells sometimes increased in number. The ganglion-cells are 

 likewise swollen, and show a diminished staining capacity, 

 vacuolization, varicosity of their protoplasmic processes, and 

 dislocation of their nucleus toward the periphery of the cell. 



At a later stage the tissue is yellow, pressure-anamia having 



