SPINAL CORD. 131 
tissue consists of neuroglia cells with their branching processes or 
fibrillee. 
What are the changes in locomotor ataxia ? 
There is a production of new connective tissue in the posterior 
columns which may also implicate the posterior portion of the lateral 
columns. There is a degeneration and atrophy of the nerve fibres. 
Very often the walls of the bloodvessels are thickened. 
To what is nerve degeneration often due ? 
Either to the destruction of the brain centre, from which the nerve 
fibre arises, or to a destruction or division of the nerve fibre between 
its point of origin and point of distribution. 
What changes take place in the degenerated portion ? 
The medullary sheath and axis cylinder become granular and fatty 
and disintegrate. The degenerated part becomes grayish in color from 
absorption and from hardening due to the formation of new connective 
tissue. From the change in color this degeneration is called gray 
degeneration. 
What are the different forms of gray degeneration ? 
Ascending and descending gray degeneration. 
What parts of the cord are affected in ascending gray degeneration ? 
The sensory nerve fibres are affected. The parts involved are the 
columns of Goll in the posterior columns of the cord. It also affects 
the direct cerebellar tract and the columns of Gowers, both situated in 
the periphery of the lateral columns of the cord. 
What parts of the cord are affected in descending gray degeneration? 
The motor nerve fibres are alone affected. The degenerated area may 
or may not be extensive, depending upon whether the fibres run a long 
or short course before passing into ganglionic centres. The portions 
affected are the columns of Tiirck in the anterior columns, and the 
pyramidal tracts in the lateral columns of the cord. 
What tumors are found in the spinal cord ? 
Tumors of the cord are rare. Fvbromata, gliomata, sarcomata, glio- 
sarcomata and neuromata have been described as primary tumors. 
Carcinoma may occur as a secondary growth. 
What is the lesion in syringomyelia? 
There is a growth of gliomatous or glio-sarcomatous tissue in the 
vicinity of the central canal, which may expand with the formation of 
cavities of greater or less extent. 
