582 DR JAMES W. DAWSON ON 



fuse and become homogeneous, and with Van Gieson's stain take a faint pink or 

 yellow tinge. The outer layers of the adventitia remain for a long time separated, 

 and contain cells of various kinds, granular debris, and blood pigment, but finally 

 these all disappear, leaving a dense, homogeneous ring, in which almost no cell 

 element can be recognised, except a very rare endothelial cell. 



The glia changes correspond to the age of the process ; on the one hand glia cell 

 proliferation is found, and on the other glia fibril formation, and the tissue has 

 altered to a dense feltwork. It is undoubtedly the large, pathological spider cells 

 that produce the fibrils, and then in great part the nuclei perish. To such a 

 disappearance and degeneration is to be traced the comparative nuclear poverty of 

 the old sclerotic area. 



It may be noted here that the glia fibril formation rarely takes place so uniformly 

 parallel to the longitudinal direction of the nerve fibres. Where the large lateral 

 blood-vessels course inwards from the surface at right angles to the long axis, they 

 interrupt the direction of the fibrils. This may partly explain the almost constant 

 radial arrangement of the glia fibrils around blood-vessels in an old sclerotic area. 

 When, too, a greater degree of degeneration has occurred or a more rapid proliferation, 

 the resulting glia fibrils will run much more irregularly (fig. 359), and, especially 

 round the blood-vessels, will form the tourbillons or whorls so frequently found in 

 sclerosed posterior columns, and also in the lateral columns. 



The above stages may be briefly described in the following terms, which 

 characterise their dominant feature : — 



(1) That of a commencing reaction of all the tissue components. 



(2) That of a glia cell proliferation and a commencing fat granule cell formation. 



(3) " Fat granule cell myelitis." 



(4) That of a commencing glia fibril formation. 



(5) That of an advancing sclerosis. 



(6) That of a complete sclerosis. 



In Weigert sections of an area in its process of evolution it is found that, in the 

 earliest stage, the low power indicates little alteration, but a higher magnification 

 shows that the myelin is swollen and diffusely and densely stained, and has not the 

 clear, ring-like defined character of the normal myelin sheath. In the second stage 

 this is even more marked amongst some nerve fibres, while others have their myelin 

 sheath broken up into a group of globules, and still others show an almost complete 

 absence of myelin within the area, but many of the fat granule cells contain granular 

 globules that retain the hsematoxylin stain, and still other granules and even 

 fragments so stained are found free in the tissue (fig. 408). In the succeeding 

 stages the Weigert picture within the area is an entirely negative One. 



Marchi-stained preparations show, even in the earliest stage, traces of a com- 

 mencing degeneration of the myelin of the swollen nerve fibre, and frequently 

 within this can be recognised, especially in sections counter-stained with safranin, a 



