Ranson, Retrograde Degeneration. 385 



irregular contour, being very much constricted at certain points 

 and swollen into beads at others. Most of these fibers stain 

 well by the Pal-Weigert method. Their myelin has not been 

 gathered into droplets nor been to any appreciable extent ab- 

 sorbed. These beaded fibers are not to be found more than 

 two millimeters on either side of the line of incision since the 

 cellulipetal degeneration had extended only a short distance 

 along the fiber. 



In a rat ten days younger (sixty days old at the time of 

 operation) there are considerable areas of degeneration in the 

 substantia alba. Figure i, "«" shows a Y-shaped area of faint 

 staining extending medialward from the scar. There is also a 

 slender unstained band extending lateralward. In these areas 

 the cellulipetal degeneration has progressed somewhat farther 

 than in the case previously described. Near the line of incis- 

 ion all the myelin has been absorbed, leaving only the faintest 

 outline of the fibers visible. Figure 2 is a drawing of a small 

 portion of the degenerated area represented at "«" in Figure i. 

 In addition to the beaded fibers described in the previous case 

 there are many that are faintly stained, some of which contain 

 minute droplets of myelin. There are also many large faintly 

 stained drops of myelin which do not appear to be connected 

 with fibers. 



In the rat which was thirty days old at the time of the op- 

 eration, the process of cellulipetal degeneration has increased 

 in intensity and extended farther along the fibers. Figure 3, 

 "«", shows a comparatively wide band in the substantia alba 

 faintly stained because of the disappearance of most of the 

 fibers. Near the line of incision this disappearance of fibers is 

 complete ; only a few scattered drops of myelin are visible. 

 Farther lateralward (Fig. 4) are fibers in the process of disinte- 

 gration, some swollen and beaded, other faintly and irregularly 

 stained. Still farther lateralward these give place to normally 

 stained, smoothly contoured fibers. 



Changes similar to those described above were found in 

 the brain of a rat operated on when twenty-one days old ; but 

 here fibers were found degenerating at a much greater dis- 



