THE HISTOLOGY OF DISSEMINATED SCLEROSIS. 605 



outer rim of the sheath is stained black, and that this degeneration gradually 

 extends inwards to involve its whole extent. 



In Heidenhain's iron-hsematoxylin sections, the nerve fibres bordering on the 

 degenerated zone have their neurokeratin framework beautifully brought out, and in 

 the spindle-shaped swellings above referred to this is seen to be a very wide-meshed 

 one. Marburg has represented the chemistry of this process as a degeneration first 

 of the lecithin, which supplies the fatty products, while the chief mass of the hsema- 

 toxylin substance (protagon) is spared longer, so the fibres which in Marchi sections 

 show degeneration are still stained in Weigert's hsematoxylin. 



In longitudinal sections of the cord it may be seen that this degeneration may 

 affect the nerve fibres " discontinuously." This is specially easily recognised in 

 Marchi sections, counter-stained with safranin, in which the retained axis cylinder is 

 seen surrounded by a pink-stained zone, which becomes gradually interrupted by a 

 portion of the fibre in which granular disintegration has commenced. The axis 

 cylinder within this affected portion may be swollen and homogeneous, but can be 

 recognised till a late stage of the degeneration. Thus this form of degeneration can 

 be distinguished from secondary degeneration by its limitation, by its late affection 

 of the axis cylinder, and, finally, by the character of its disintegration into granules 

 and globules (fig. 320) instead of at once into coarse balls and fragments (fig. 324) 

 which fill the whole myelin sheath. The fat granule cells, which are found in such 

 large numbers, could only in rare instances be found to contain large fragments of 

 myelin. It seemed rather as if a gradual absorption of dissolved substances had 

 taken place, and that these within the cell had become transformed into fine 

 fat-like granules. 



In the " Markschattenherde " we may have simply a deficient staining of the 

 whole myelin sheath, or there may be only a thin ring of myelin around an almost 

 normal axis cylinder. Volsch assumes that in the latter case there has been a gradual 

 atrophy of the myelin, and then a persisting condition of the remainder. 



It may finally be noted that in some areas certain fibre-systems seem to be more 

 resistant. In areas of sclerosis involving both the anterior horn and the entire 

 antero-lateral tract the intra-medullary anterior root fibres were frequently found 

 intact, or showing only slight Marchi degeneration. Similarly the external arcuate 

 fibres in the medulla oblongata seem to be relatively long preserved. 



(b) Axis Cylinder. 



The comparative persistence of the axis cylinders in the sclerotic area has long 

 been regarded as one of the essential characteristics of disseminated sclerosis. 

 Charcot himself, from the apparent disproportion between the symptoms and the 

 anatomical lesions, argued for their persistence. The earlier observers undoubtedly, 

 with diffuse stains, frequently mistook the longitudinal glia fibrils, which run parallel 

 to the degenerated nerve fibres, for true axis cylinders, yet modern specific staining 



TRANS. ROY. SOC. EDIN., VOL. L, PART III (NO. 18). 85 



