THE HISTOLOGY OF DISSEMINATED SCLEROSIS. 591 



(fig. 449), and the areas affected, around each vessel, usually coalesce to form a 

 more or less large irregular non-myelinated area. Frequently half the vessels 

 affected lie within non-myelinated tissue, and half within tissue in which the 

 myelin as yet stains normally (fig. 450). Borst considered that these areas are 

 the result of a circumscribed peri-vascular lymph congestion and that they are 

 a pre-stage of areas of true dense sclerosis, which, he considers, develops on the 

 basis of a lymph stasis in the tissue. 



(c) " Markschattenherde." 



As a rule, at least at the commencement of the process, sclerotic areas have 

 a very limited longitudinal and transverse extent. This characteristic has 

 given to the disease the name " insular sclerosis," because the areas appear 

 isolated. We have seen, however, that areas frequently coalesce on one or 

 several sides, and the original outlines are quite indistinct. In addition to this, 

 there are often found between individual non-myelinated areas, extensive patches 

 which, with Weigert staining, show a weak staining of the myelin. The fibre 

 bundles are distinctly perceptible and yet scarcely stained : this is well brought out 

 on longitudinal sections, where it is seen that the fibre layers correspond in 

 arrangement and position to the normal bundles, and one can recognise the 

 immediate transition of normal fibres into those with deficient staining. Such 

 areas, in which the myelin sheaths are simply shadows or very thin, adjoin areas 

 of complete demyelination, and may involve the whole transverse section or the 

 longitudinal section over several segments. Alzheimer looks upon this deficient 

 staining as a condition of the myelin sheath antecedent to degeneration. Marchi 

 staining sometimes gives a very extensive early degenerative process, and there 

 may be an equally extensive commencing glia proliferation. Yet this change may 

 sometimes indicate a simple atrophy which results in a progressive reduction of the 

 volume of the sheath without affecting the remaining myelin. The process might 

 then be looked upon as a slumbering one, and not necessarily immediately antecedent 

 to degeneration. In the former case the glia proliferation would be more abundant, 

 as the slow, chronic stimulus would be more likely to lead to a greater reaction in 

 the interstitial tissue. Thus Volsch has described areas in which there was a very 

 extensive " Aufhellung " of the myelin sheath, which was associated with an equal 

 or even greater degree of glia hyperplasia — a condition which he has termed " diffuse 

 multilocular sclerosis." 



It may finally be noted that in Marchi sections there was frequently found, 

 extending outside the sclerosed areas uniformly over the whole transverse section 

 of the cord, an early myelin sheath degeneration. This could be noted even in 

 the nerve roots and must, probably, be traced to the septic fever from which the 

 patients suffered. 



