434 VEDDER AND CLARK. 



which are usually characterized by the rapid recovery of the 

 fowl, indicate that they do not. These fibers showing advanced 

 degeneration are marked by the accumulation of myelin in large 

 globules and droplets, a swelling and bulging of the nerve sheath 

 at these points, and a disintegration of the axis cylinder. The 

 largest globules usually appear vesicular and, in their center, 

 segments or fragments of the axis cylinder are frequently to 

 be seen. In these larger and some of the smaller globules 

 the stainable material is found at the periphery and appears 

 laminated. This laminated appearance is very characteristic in 

 Weigert preparations and is the rule in the larger globules. 

 Usually 3 distinct layers are clearly visible of which the outer 

 is the thickest. Other incomplete layers and fragments are seen 

 centrally. The larger globules of degenerated myelin are not 

 in proximity with one another; they are separated by at least 

 many microns. The space between contains a few small droplets 

 of degenerated myelin. It seems otherwise almost or quite 

 devoid of structural contents. In other fibers the change appears 

 just as complete and the segments and globules of the degen- 

 erated myelin are just as evident, but the globules are uniformly 

 smaller. The same fiber may and probably does show both 

 conditions at different places along its course. 



Plate II, fig. 3, h, shows a nerve fiber in which degenerative 

 changes are well marked. None of the largest globules are 

 shown. Small droplets are seen between the larger globules in 

 the otherwise apparently empty space. In this fiber the change 

 of myelin into fat seems complete, while in fiber, c, the myelin 

 seems intact and quite normal in appearance. It will be noted 

 that here and there the degenerated myelin fails to fill the 

 neurilemma sheath. Thus an apparently empty space is left 

 between the latter and the degenerated myelin. This is in con- 

 trast to the condition found in those fibers containing the largest 

 globules. Here the globule fills and distends the neurilemma. 



In addition to the appearance just noted, other fibers were 

 seen, in the nerves where degeneration was most marked, in 

 which the degenerated myelin was confined to small droplets 

 which failed still further of filling up the neurilemma sheath. 

 Here segments of the axis cylinder were less frequent, but 

 the more or less indistinct granules which were taken to be 

 fragments of the axis cylinder were more numerous. In others 

 the neurilemma sheath appeared much shrunken or collapsed, 

 and a few small droplets of degenerated myelin were contained 

 within. 



