604 DR JAMES W. DAWSON ON 



tion of small round cells. These meningeal changes, when present, are usually diffuse 

 and in no way confined to the meninges overlying areas of sclerosis. 



(4) Changes in the Individual Tissue Elements. 



1. Nerve Fibres, 

 (a) Medullated Sheath. 



In the actual sclerotic areas the medullated sheaths have entirely perished, but 

 in recent areas and at the advancing peripheral zone of older areas the changes 

 present themselves in very various forms, according to the stages of the degenerative 

 process, and according to the greater or lesser intensity of the process. In Weigert 

 transverse section, the myelin sheath may appear deficiently stained, or there may 

 be only a thinning of myelin, but more often it is diffusely stained and swollen, or 

 the whole ring of myelin may be broken up into a number of finer and larger 

 globules (fig. 408). On longitudinal section, however, the process may be much 

 more readily studied in its individual stages, and the fibres, especially in the transi- 

 tional zone of an advancing area, may show all conceivable types (figs. 406, 407). 

 The varicosity so frequently found even in normal fibres is greatly exaggerated, and 

 the whole fibre may be represented by a series of large oval vesicles, the outer rim 

 of which stains with hsematoxylin. Frequently, and this seems to me the most usual 

 type, a number of very fine granules and balls are attached to the outer border of 

 the myelin sheath ; some of these tiny balls seem to burst, and gradually others 

 re-form till the myelin sheath projecting into an area is gradually more and 

 more thinned, and is finally represented by a series of very delicate globules. 

 Some of these may be found for a considerable time in the degenerated area, 

 retaining the heematoxylin stain. One rarely meets with the very swollen, 

 tumefied, badly-staining fibres such as are found in softenings, although the 

 destruction of the myelin seems to start in an cedematous swelling analogous 

 to that found in acute myelitis. 



In Marchi sections (figs. 319-323) the actual degeneration shows first as long 

 parallel rows of droplets which darken with the osmic acid. These are again most 

 frequently on the outer edge of the nerve fibre, and may be only on its one side. 

 Such fibres on transverse section would appear as if a crescentic part of the sheath 

 were affected. Sometimes there are double rows of droplets or granules within one 

 myelin sheath. The appearance of these rows of granules is often, but not always, 

 preceded by a varicose condition of the fibres, extending over long distances ; the 

 swelling affecting the whole sheath and appearing either in the form of small beads 

 or large spindle-shaped vesicles, which may perhaps represent an acuter process, or 

 one accompanied by more oedema. Within these swellings the sheath may then 

 show the fine granular degeneration, and these granules may run together. On 

 transverse Marchi sections it is frequently possible to recognise that an entire 



