Ranson, Retrograde Degeneration. 387 



might be interpreted as due to a failure of development of the 

 medullary sheaths about the central portions of the severed ax- 

 ones; or it might be due to the complete disappearance of these 

 axones. But when one takes into consideration the retrograde 

 degeneration seen in these fibers in the older rats, there can be 

 little doubt that the degeneration is of the same nature in these 

 younger animals and that the entire neurone has undergone dis- 

 integration. 



If it is remembered that all these animals were allowed to 

 live for one month and a half after the operation, it will be seen 

 from what has been said that the intensity of the cellulipetal de- 

 generation exhibited in any portion of the section depends upon 

 two variables, the age of the animal and the distance between 

 the point of observation and the point of injury. In the oldest 

 rat the process was confined to a small portion of the fiber near 

 the lesion. As we pass down the series from the oldest to the 

 youngest animal, the degeneration increases in intensity in the 

 vicinity of the lesion, and extends to a greater distance from 

 the point of injury. The complete degeneration of the fibers 

 in the older rats takes place only in the immediate vicinity of 

 the lesion, but in the youngest animal the fibers degenerate 

 completely throughout their entire length. 



There are several respects in which the changes here de- 

 scribed differ from the Wallekian degeneration. In typical 

 secondary degeneration the myelin begins to liquify at the sixth 

 day and is largely absorbed before the twentieth. But in the 

 milder cases of the degeneration here described there are many 

 fibers remaining after forty-five days which differ from the nor- 

 mal only in the presence of a few beadlike swellings, the rest of 

 the fiber remaining normal in contour and staining properties. 

 And in these milder cases there are no fibers present in which 

 the myelin has undergone liquefaction. It is evident that the 

 secondary degeneration, which must have occurred in the por- 

 tions of the fibers separated from their cell bodies, has run its 

 full course and the resulting debris been entirely absorbed. 

 Otherwise we could not account for the complete absence in 

 some of these cases of fibers in the last stages of degeneration. 



