SPINAL CORD. 473 



fibers in sections stained with carmin or anilin blue-black appear 

 as clear areas with the stained axis-cylinder in the center, the 

 clear space being the medullary substance. 



The gray matter consists of nerve-fibers, of nerve-cells and 

 their processes, together with neuroglia and blood-vessels. 



Tracts of the Cord. The course which the nerve-fibers 

 take in the columns of the cord has been determined by two 

 methods : the embryologic and the degenerative. 



The embryologic method, or method of Flechsig, consists in 

 studying the cord at different stages of its development ;. and as in 

 some tracts the medullary substance forms at an earlier period 

 than in others, these can be thus differentiated or distinguished 

 from one another. 



The degenerative, or Wallerian, method consists in studying 

 the degeneration which occurs in nerve-fibers when separated 

 from their nutritive or trophic centers (p. 464). Sections of the 

 cord in which the degeneration has taken place are stained with 

 Marchi's solution, consisting of Miiller's fluid 2 parts, and 1 per 

 cent, osmic acid 1 part : the degenerated fibers stain black, while 

 the other portion remains practically unstained. A tract in which 

 this degeneration takes place below the injury or point of section 

 is a descending tract, and the degeneration is a descending degenera- 

 tion; while a tract in which the process occurs above the lesion 

 is an ascending tract, and the change, an ascending degeneration. 



These methods have demonstrated the following tracts in the 

 cord (Fig. 271), into which the main columns may be considered 

 as divided. Each tract or fasciculus may be considered, Gray 

 says, as a distinct anatomic system and endowed with special 

 functions : 



1. Direct Pyramidal Tract. This is also called fasciculus of 

 Turck, and is situated in the anterolateral column next to the 

 anterior median fissure. It is continuous with the non-decussating 

 fibers of the pyramid of the medulla. Besides this tract, the 

 anterolateral column contains : 



2. Grossed Pyramidal Tract. The fibers of this tract are con- 

 tinuous with those forming the decussation of the pyramid of the 

 medulla. 



3. Direct Cerebellar Tract. Continuous with the restiform 

 body. 



4. Anterolateral Ground-bundle. Continuous with the forma- 

 tio reticularis of the medulla. 



5. Anterolateral Descending Cerebellar Tract (Lowenthal). 



6. Anterolateral Ascending Cerebellar Tract (Gowers). 



7. Tract of Lissauer. 



The posterior column contains : 



8. Poster omedian, also called posteromesial and column of Gfoll, 

 which is continuous with the funiculus gracilis of the medulla. 



