66 ELBEIIT CLARK 



illustrate the marked degeneration described, and figure 6 shows 

 segments of axis cyhnders enclosed within large globules. 



Howell and Huber ('92), Bethe ('07), Mott, Halliburton and 

 Edmonds ('04), Cajal ('05),Ranson ('12), and others have observed 

 that after section not all meduUated fibers degenerate with equal 

 rapidity. As noted, this is particularly true of degeneration in the 

 fibers of the sciatic in fowls on a white rice diet. In the nerves 

 of these fowls, a fiber showing the first indication of degener- 

 ation may be found side by side with one in which the neuraxis 

 and medullary sheath are completely broken up (fig. 7). 



These few remarks, with the accompanying figures 2 to 7, 

 make it clear that paralysis in the rice-fed fowls presents an 

 experimental condition resulting in degeneration in which almost 

 every stage of the process is to be observed in the same nerve 

 at one and the same time, in which the continuity of the fibers 

 is not disturbed, where reaction to trauma is obviated and where 

 degeneration, though proceeding rather rapidly, is much slower 

 than after section of the nerve. 



THE EMBRYONIC NERVE FIBER 



Rapid multiplication of the nuclei of the sheath of Schwann, 

 coincident with the change in the medullary sheath and axis 

 cylinder, has been a constant finding with all those observers 

 who have studied degeneration of nerves after section. It was 

 a little surprising to find it not to obtain in the present case 

 which in every other respect resembles Wallerian degeneration 

 and in which the process of degeneration is also rapid. A care- 

 ful search of both teased and sectioned preparations of nerves, 

 taken at time of paralysis and in which the nuclei were well 

 stained, failed to reveal any marked or definite increase in the 

 number of nuclei of the neurilemma sheath or any structure 

 which could be definitely identified as an embryonic nerve fiber 

 in the degenerated fibers of a single fowl. 



An explanation of this marked variation was of course required, 

 and inasmuch as fowls frequently recovered after the most marked 

 paralysis of the legs, it became necessary to determine if regen- 

 eration occurs in that 10 to 20 per cent of fibers which show 



