MYELITIS. 213 



Inflammation may also travel to the cord along the connective 

 tissue sheaths of the nerves, and the so-called "reflex urinary 

 paraplegia" is probably an example of this method of invasion. 



The distinction of a mere softening of the cord, the result of 

 vascular occlusion, from the softening which is the result of 

 inflammation is not at all easy. The myelitis which is met with 

 within a couple of years of syphilitic infection is, with considerable 

 reason, regarded by many as a primary vascular softening. In 

 such cases the vascular obstruction must be the result of endar- 

 teritis of minute terminal vessels in the cord, for there is a free 

 vertical anastomosis not only of the spinal arteries on the surface 

 of the cord but also, to a less degree, of the larger arteries in the 

 cord itself. 



As the result of myelitis the nervous structures at the site of 

 the disease are more or less destroyed, but, in addition to this, 

 certain secondary degenerations of the cord are found. These 

 secondary degenerations occupy definite tracts in the white 

 matter, and some ascend from the site of lesion whilst others 

 descend. The degeneration of these tracts is dependent on their 

 severance from their trophic cells. The descending degenerations 

 involve the crossed and direct pyramidal tracts, whilst tracts 

 which undergo ascending degeneration are the direct cerebellar 

 tract, the antero-lateral ascending tract of Gowers, and the tracts 

 which form the postero-internal and postero-external columns of 

 the cord, or the column of Goll and the column of Burdach. 

 (Fig. 19, p. 222.) The lumbo-sacral fibres of the postero-external 

 column do not pass up to the bulb in this column, but after a 

 short upward course enter the postero-internal column and com- 

 plete their ascent in this. Consequently the postero-external 

 column is only degenerated for a short distance above the lesion, 

 whilst the degeneration in the postero-internal column passes as 

 high as the grey matter of the nucleus gracilis. The higher the 

 lesion the more complete the degeneration of the postero-internal 

 column, since the nerve fibres which enter it from the upper 

 lumbo-sacral sensory roots are affected as well as the lower. 



But inflammation may also extend from the local lesion for a 



