530 S. AVALTEK HANSON 



tions 20 days after division of the corresponding nerve roots. 

 They are limited quite sharply to the medial half of the tract, 

 the lateral half being free from degenerated fiber's. 



In Pal-Weigert preparations at the level of the injured roots 

 one sees that the medial part of Lissauer's tract is more lightly 

 stained and contains fewer fibers on the operated side than on 

 the normal side, while there seems to be no change in the number 

 of fibers in the lateral part of the tract (figs. 1 and 2). Figure 2 

 represents a part of the tract on the injured side of the cord; the 

 right side of the drawing is from the medial half of the tract and 

 the left side from the lateral half. It will be seen that there is a 

 marked reduction in the number of medullated fibers in the medial 

 as compared to the lateral half of the tract. Normally the medial 

 and lateral halves of the tract have about the same number of 

 medullated fibers. 



As to the length of the dorsal root fibers within Lissauer's tract, 

 the best information is given by Marchi preparations from Cat 

 VIII, in which the sixth and seventh lumbar roots were cut. 

 In the sixth and seventh lumbar segments there is a well-defined 

 degeneration in the medial half of Lissauer's tract as seen in 

 figure 3. In the fifth lumbar segment, the first segment above 

 with intact roots, there is a much smaller number of degenerated 

 fibers and these are present only in the medial half. In the fourth 

 lumbar segment, the second above with intact roots, there are a 

 very few degenerated fibers in the medial half of the tract. In 

 the third lumbar segment there are none. It thus appears that 

 some of the medullated fibers run upward one segment, and a 

 very few as much as two segments. In a downward direction the 

 medullated fibers do not extend so far. In the upper part of 

 the first sacral segment, the first below with intact roots, there are 

 a few degenerated fibers in the medial half of Lissauer's tract; 

 but in the lower part of this segment there are very few indeed. 

 If a section through the lowest part of the seventh lumbar seg- 

 ment is compared with a section through the highest part of the 

 sixth Imnbar segment (Cat VIII, L, 6 and 7 roots cut), it is seen 

 that the nmiiber of degenerated medullated fibers which extend 



