440 VEDDER AND CLARK. 



globules of degenerated myelin. This is especially evident at 

 a, which gives the appearance of a globule from which much 

 of the fat has been dissolved by the clearing agent. 



It might be claimed that, since the spinal cord gives off two 

 spinal nerves at each segment of the vertebral column, the 

 fibers described above might represent primary fibers from the 

 nerve roots of these spinal nerves. We recognize this as a pos- 

 sibility in many cases. However, it must not be forgotten that 

 the fibers of Goll's column (ascending) are secondary neuraxes 

 of sensory fibers which enter the cord in the lumbosacral region ; 

 that is, that they are axis-cylinder processes of cells situated 

 in this portion of the cord. It might be further pointed out 

 that the more mesial fibers arise from cells in the lower seg- 

 ments of the cord. Now, since fibers a and a', fig. 11, are such 

 mesial fibers, it follows that they can not be fibers of the nerve 

 roots of the thoracic spinal nerves, but are fibers of Goll's column 

 showing degeneration. 



If the medullary sheath of the fibers within the cord shows 

 myelin degeneration, it is natural to inquire into the state of 

 the axis cylinder. Longitudinal and transverse sections of the 

 thoracic region of the cord have been examined after staining 

 by the various methods noted above for the axis cylinder. 

 Appearances of degeneration similar to those described for the 

 axis cylinder of certain fibers of the sciatic have been noted 

 in the fibers of all columns of the cord. These changes consist 

 in segmentation and fragmentation which are evident only in 

 longitudinal sections of the cord and granulation which is best 

 seen in transverse section. We were unable to determine whe- 

 ther relatively more fibers show a breaking up of the axis 

 cylinder in one column than in another. This is due to several 

 reasons. We have no stain distinctly specific for the axis cylin- 

 der. The Golgi, Cajal, and other metallic methods besides 

 bringing out other structures can not be relied upon to impreg- 

 nate every axis cylinder ; it is very difficult to stain a degenerating 

 axis cylinder, and small corpora amylacea and neuroglia cells 

 with their small amount of surrounding connective tissue might 

 easily be mistaken for cross section of such a fiber. 



Plate V, fig. 10, which is from the posterior lateral column 

 of the thoracic cord of a fowl with well-marked neuritis, shows 

 at a and a' two fibers with degenerating axis cylinders. The 

 axis cylinder shows a granular or somewhat flocculent appear- 

 ance, and probably represents an advanced stage of degenera- 

 tion. As the columns of the cord are not well demarcated, we 



