420 S. WALTER RANSON 



counter-stain of the axons is obtained. The pyramidal tract 

 stains intensely with the fuchsin because of the predominance of 

 axon substance in its composition. 



Non-medullated fibers are also found in other parts of the 

 white substance of the rat's spinal cord but are much less numer- 

 ous than in the pyramidal fasciculus. 



It should be added that all these observations were made on 

 well developed adult rats, and are not to be explained by an 

 immaturity of the individual animals employed. 



These observations on the character of the fibers in the pyra- 

 midal tract of the white rat were made in connection with a 

 search for the path within the spinal cord taken by the non-med- 

 ullated fibers of the dorsal roots (Ranson '12). It is conceivable 

 that they might run into the ventral portion of the posterior 

 funiculus and ascend in the region occupied by the pyramidal 

 tract; and since the number of non-medullated fibers from the 

 dorsal roots is very considerable, such ascending fibers might 

 represent all of the non-medullated fibers seen in this part of 

 the cord. That is to say, the tract described in the first part 

 of this paper might be a mixed one consisting of descending med- 

 ullated fibers from the motor cortex and ascending non-medul- 

 lated fibers from the dorsal roots. 



In order to rule out this possibility, the following experiment 

 was performed on adult albino rats. Under aseptic precautions 

 the sciatic nerve was exposed in the upper part of the thigh, grasped 

 with artery forceps and torn out of the pelvis. Five experiments 

 were made. In one case two dorsal roots and their ganglia came 

 away with the sciatic, in the remaining four only one root and 

 ganglion. Each animal was killed after from twenty-four to 

 twenty-eight days. No attempt was made at the autopsy to 

 determine which of the roots associated with the sciatic was torn 

 away in the operation. Pyridine-silver preparations were made 

 of the lumboscaral portion of each of these cords. A varying 

 degree of degeneration was seen in the last lumbar segments, 

 depending upon the amount of damage done to the ganglia and 

 roots when the sciatic was torn out. But in each case a very 

 definite degenerated area could be seen, from which most of the 



