lissauer's tract 539 



upward into the fifth lumbar is much greater than the number 

 which extend dow^nward into the first sacral segment. 



Both figures 1 and 2 were taken from a section at the middle 

 of the sixth lumbar segment 74 days after the sixth and seventh 

 roots had been destroyed, and represent the maxunum amount of 

 degeneration of medullated fibers obtainable in Lissauer's tract 

 by destruction of the dorsal roots. We say that it is the maxi- 

 mum, because the time allowed for the degeneration is adequate 

 and because, as we have seen, very few medullated root fibers 

 ascend more than one and a half or descend more than half a 

 segment in the tract of Lissauer. It is doubtful if destroying 

 the fifth lumbar and first sacral roots in addition to the sixth and 

 seventh Imnbar would have caused the disappearance of any more 

 of the fibers from the tract in the middle of the sixth Imnbar seg- 

 ment. 



In view of these facts, it is clear that the fibers indicated in 

 figure 2 are all or nearly all endogenous. That is to say, in the 

 lateral half of Lissauer's tract (in the sixth lumbar segment of the 

 spinal cord of the cat) practicallj' all of the medullated fibers are 

 endogenous, while in the medial half a large nmnber, perhaps 

 50 per cent, are endogenous. 



The degeneration of the non-medullated fibers can not be 

 followed in so definite a way as that of the medullated fibers, since 

 we have no stain for degenerated axons smiilar to the Marchi 

 stain for degenerated myelin. It must be studied in a negative 

 way, just as the degeneration of medullated fibers is studied in 

 Pal-Weigert preparations; i.e., we have only the disappearance 

 of the fibers as an evidence of degeneration. Furthemiore, the 

 change seen in pyridine-silver preparations will be due to a dis- 

 appearance of both medullated and non-medullated axons, and 

 it will be necessary, therefore, to speak of it as a degeneration 

 of axons, with the understanding that the majority of the axons 

 that disappear are non-medullated. Figure 5 illustrates how 

 the degeneration of axons is shown by pyridine-silver preparations. 

 About half of the tract of Lissauer takes the stain normally. 

 This is the part situated lateral to the point of entrance of the 



