638 DR JAMES W. DAWSON ON 



that no clinical or anatomical distinction exists between the two. A.n intermediate 

 position is taken up by those writers who reconcile the inflammatory theory with 

 the developmental one. They admit that congenital anomalies of the glia may 

 become the point of origin of primary proliferations of the glia, but they believe that 

 the blood-vessels distribute some toxi-infectious agent which settles there where the 

 glia is abnormal, and thus calls this glia proliferation into being. 



Turning now to the histological observations, it is necessary to ask : Do these 

 throw any light : 



(1) Upon the Nature of the Process? — Do the areas arise solely upon the basis 

 of a gradually increasing glia hyperplasia, or on the basis of an inflammatory 

 reaction, or on both ? Further, are there sufficient grounds for distinguishing 

 between the two ? 



(2) Upon the Origin of the Process ? — If we admit a primary form of dis- 

 seminated sclerosis of developmental nature, we have answered the question of its 

 origin in the glia ; but if we say that the underlying process is of an inflammatory 

 nature, we thereby also say that the blood-vessels or lymph channels carry the 

 ultimate causal factor to the tissues, but must further decide on which tissue 

 element there is the first evidence of its action. 



(3) Upon the Etiological Factors postulated — chill, trauma, psychic shock, 

 intoxications, infectious diseases, etc. ? 



(4) Upon the Mode of Action of the Causal Agent, and the other questions 

 which this consideration involves ? 



For the purposes of our argument it is assumed that the cases investigated were 

 cases of disseminated sclerosis. This follows (l) from the clinical notes submitted ; 

 (2) from the macroscopic findings of disseminated areas in spinal cord and brain, 

 with the characters usually ascribed to this disease ; (3) from the recognised micro- 

 scopic characters of these isolated or confluent areas in which were found absence 

 of the myelin sheath of the nerve fibres, and varying degrees of glia proliferation, 

 blood-vessel changes, and persistence of axis cylinders. 



(l) Nature of the Pathological Process. 

 1. Developmental. 

 MtiLLER has strongly upheld the view of the developmental nature of dis- 

 seminated sclerosis, and has emphasised the distinction between the primary and 

 secondary forms of the disease. Weigert's work showed that both from the 

 morphological and biological points of view the neuroglia reacts as a true connective 

 tissue. Muller's wider conception of this idea leads him to see that the ultimate 

 product of processes entirely different in their pathogenesis, but presumably all 

 giving rise to focal disease of the parenchyma, may show disseminated sclerotic 

 patches. He divides them, on the one hand, into those processes which always 

 occur as the direct result of exogenous factors and lead to multiple focal degenera- 



