STUDY OF POLYNEURITIS GALLINARUM. 435 



A careful study of all these fibers has convinced us that the 

 successive stages of myelin degeneration correspond pretty well 

 with the order just described. The earliest stage made apparent 

 by the Marchi method consists of a slight swelling of the medul- 

 lary sheath, which shows a diffused blackening with the osmic 

 acid and slight tendency toward segmentation at the circum- 

 ference. Plate II, fig. 3, a, and Plate IV, fig. 7, show such fibers.^ 



Then follows the stage in which the largest globules distend- 

 ing the nerve are seen. Next is the stage in which the globules 

 are much smaller, though quite black and discrete, and which 

 only partly fill the sheath of Schwann. In the succeeding stage, 

 the globules are very small but numerous. Then follows a stage 

 where the shrunken neurilemma contains only a few scattered 

 droplets of fat. 



The neuraxis. — As stated above, the axis cylinder in those 

 nerve fibers which show marked degeneration usually appears 

 broken up. In the larger globules of myelin and at other places, 

 segments of the axis cylinder were to be seen. Plate V, fig. 9, 

 shows such a fiber. The granular appearance of the axis cylinder 

 as is shown in this figure is quite typical for axis cylinders in 

 fibers of this type. The segments enclosed within the globules 

 of myelin which are usually curved or somewhat S-shaped also 

 show this granulation when stained in certain dyes; carmine, 

 acid fuchsin, Mallory's phosphomolybdic acid, hsematoxylin, etc. 



It might be remarked in this connection that many authors 

 hold the view that the axis cylinder contains many neurofibrillse 

 along whose course many fine granules or enlargements are 

 scattered. In those fibers in which the degeneration is further 

 advanced, the remains of the axis cylinder is seen; not as a 

 segmented, but rather as a fragmented structure. The frag- 

 ments appear rather indistinct and diffuse and contain small 

 obscure granules. The appearance somewhat simulates in sec- 

 tion coagulated exudate or serum. Plate V, fig. 10, a. illustrates 

 the appearance of a fragmented axis cylinder after staining 

 with haematoxylin and acid fuchsin. In each fiber showing 

 advanced myelin degeneration the axis cylinder was broken up. 

 Segments of the axis cylinder are to be seen in all the large 

 globules if properly stained. Whether the breaking up of the 

 axis cylinder precedes or follows the formation of the large 



■* A diffuse blackening of the myelin, however, may be obtained even in 

 a normal nerve by too short a mordanting in the Miiller's fluid or by pro- 

 longed staining in Marehi's mixture. The tendency to segmentation though 

 is absent. 



