506 S. WAl/rER R ANSON 



side is sharper than could \)o ()l)tainod by the Marchi stain, since, 

 as Miss King has shown, few of the niedullated fibers are suffi- 

 ciently large and well medullated to give a good Marchi stain. 

 In the silver prepai'ations the degenerated pyramidal fibers 

 ha\'e disappeared and the somewhat shrunken area of the tract 

 is occupied by neuro'^ia which stains a hght yellow hi sharp 

 contrast to the normal tract which is packed with deeply stained 

 fine axons. Scattered through the degenerated area are a few 

 normal fibers. These either represent pyramidal fibers from 

 p(M'tions of the motor cortex that escaped injury or an admixture 

 of endogenous fibers in the pyramidal tract. Some of these 

 normal fibers were seen in the degenerated area in all of the cords. 



The contrast between the normal and degenerated tracts 

 was not nearly so sharp in Pal-Weigert preparations. For this 

 there are three reasons. In the normal tract the myelin sheaths 

 are very thin and inconspicuous; and the entire area much 

 lighter than the surrounding white substance. There was a 

 considerable number of normal-looking medullated fibers in the 

 degenerated tract. These must either have come from unin- 

 jured parts of the motor cortex or have been of endogenous 

 origin. Furthermore, the period of 45 to 60 days did not prove 

 sufficient for the complete absorption of the degenerated myelin 

 sheaths, the remains of the degenerated myelin showing in Pal- 

 Weigert preparations as tiny blue spots. Because of the normal 

 faint staining of the tract and the survival in the degenerated 

 tract of a considerable number of normal medullated fibers, 

 the contrast between the normal and operated sides would not 

 be pronounced even after all the degenerated myelin had been 

 absorbed. As it is, with the remains of the degenerated myelin 

 sheaths showing as tiny blue spots the degenerated tract is scarcely 

 lighter than normal and it requires the use of the higher power 

 lenses to determine which side is degenerated. 



It may be that in the minds of some who have read the accounts 

 of the results obtained with the pyridine-silver method on the 

 spinal cord there may have been a suspicion that neuroglia 

 fibers were being confused with nerve fillers. Although there is 

 an abundance of other reasons for ruling out the possibihty of 



