618 DR JAMES W. DAWSON ON 



expression in dilated adventitial lymph spaces, distended glia meshes, and a swelling 

 of the contained myelin sheath and axis cylinder. In uncomplicated cases only 

 occasional and insignificant variations in the soft meninges were present, yet it must 

 be admitted that changes, if minute, might readily escape observation. 



(c) Cell Elements in the Vessel Walls. 



The statement is frequently made that infiltrations are met with in recent areas, 

 and such cell infiltrations of the adventitial sheath are considered characteristic of 

 the inflammatory process in the nervous tissue. In numerous references to the cell 

 elements of the adventitia, an endeavour has been made to show that the first cell 

 infiltration is one associated with resorption processes (fig. 13) ; that this is followed 

 by a cell proliferation in the adventitia, which is probably a secondary reaction 

 process to the presence of the first cells in the lymph spaces (fig. 437) ; and that, 

 finally, we have a more or less marked degree of cell infiltration which is character- 

 istic of a chronic inflammatory process in any tissue (fig. 14). 



In the earliest stage, as a rule, there is no evident increase of the nuclei in the 

 vessel wall, but sometimes a slight proliferation of capillary endothelial nuclei and 

 adventitial nuclei is found, which may be related to the production of fat granule 

 cells. In the stage of secondary reaction to the presence of the fat granule cells, the 

 resultant cells in the adventitia are of two kinds : the one, with large nucleus and 

 clear chromatin framework, have probably arisen from the endothelial nuclei of the 

 lymph spaces, the other, with darker-stained nuclei, from the proliferation of the 

 connective-tissue elements of the adventitia. In the third stage, in which the cell 

 infiltration partakes of the characters of a chronic process, we have mostly lympho- 

 cyte-like cells, with a darker nucleus than any of those mentioned above, a few 

 plasma cells and mast cells, together with pigment accumulations, either free in the 

 spaces or within cells, and granular debris of various kinds (figs. 14 and 439). The 

 subsequent fibrous thickening of the vessel wall in the advancing sclerosis has been 

 traced by Lhermitte and Guccione to the transformation of plasma cells into fibro- 

 blasts. In this investigation quite characteristic plasma cells were present in 

 extremely few sections. Schob, Oppenheim, and Siemerling and Raecke found 

 them in numerous instances and look upon them as the expression of a more or less 

 chronic process. Volsch and Flatau and Koelichen think most of the cells in late 

 stages belong to the lymphocytes, and that plasma cells are rarely found in the vessel 

 walls or in the meninges. 



(5) Other Histological Features. 



1. Form, Symmetry, and Distribution. 



Rossolimo first drew attention to the dependence of the sclerosed areas upon the 

 topographical distribution of the blood-vessels. As the causal agent spreads itself 

 by the blood channel, or the lymph channel accompanying the vessels, it was 



