THE HISTOLOGY OF DISSEMINATED SCLEROSIS. 637 



constituent elements of the nervous tissue — the neuroglia, the true nervous elements, 

 or the blood-vessels. The views as to the developmental nature of the process are 

 usually related to defects in the glia tissue, though a few writers refer to a " con- 

 genital degenerescence " of the true nervous elements. The views as to the 

 inflammatory nature of the process are related again to primary changes in any of 

 the tissue elements, and the factor or factors which bring the inflammatory changes 

 into operation are admitted to circulate in the blood-vessels or lymph channels, and 

 to exert their action primarily on the glia, the myelin sheath of the nerve fibres, or 

 on the blood-vessel wall itself. 



The two views as to its nature strike at the very root of the chief difficulties met 

 with in explaining the evolution of the morbid changes. The inflammatory nature 

 of the process, in some form, was admitted by most of the earlier observers, who 

 traced it chiefly to a primary change in the glia. This theory was later upheld, 

 especially by French writers, who, however, traced the process chiefly to inflam- 

 matory changes in the vessel walls, but such an explanation has appeared less certain 

 since the works of Strumpell and M tiller. These writers stated that the special 

 evolution of the disease, with its frequent marked remissions followed by aggrava- 

 tions without apparent cause, was difficult to reconcile with the view of a toxic or 

 infectious cause alone having engendered the condition. They also point out that 

 inflammation as a rule alters rapidly the axis cylinders and ganglion cells, which in 

 disseminated sclerosis are frequently preserved, and, further, that inflammatory 

 phenomena are often very difficult to trace. Recent research has greatly diminished 

 the importance of these arguments by showing both that the long duration of the 

 affection takes from the negative finding of inflammatory phenomena much of its 

 significance, and that, even in disseminated sclerosis, the ganglion cells and axis 

 cylinders frequently perish. 



For more than a quarter of a century after Charcot gave the first clinical and 

 anatomical picture of the disease, it was looked upon as a distinct morbid entity, a 

 chronic disease in which certain characteristic clinical and anatomical features were 

 always present. Many later writers, however, have related it to a disseminated form 

 of myelitis. They assert that previously only the final stages of the disease have 

 been considered, and that, by suitable staining methods, areas may frequently be 

 observed in the same case in all stages of development, from an area of inflammation 

 into an area of sclerosis, from which all traces of inflammation have disappeared. 



To this argument it is replied that there exist two forms of the disease : a 

 primary chronic form due to a malformation of the glia, and a secondary myelitic 

 form en rapport with infection and intoxication. It is admitted, however, that in 

 primary disseminated sclerosis the development of the focus may begin under the 

 reaction of external factors as agents provocateurs, but the disease is in no sense 

 dependent upon these. In opposition to this, it is asserted that the separation into 

 primary and secondary disseminated sclerosis is an artificial and arbitrary one, and 

 TRANS. ROY. SOC. ED IN., VOL. L, PART III (NO. 18). 89 



