528 DR JAMES W. DAWSON ON 



special predisposition to the development of plaques. He remarks, however, that 

 they are rarely found in the grey substance of the convolutions. Regarding the 

 macroscopic characters of the areas, Charcot noted that they were sometimes 

 turgescent, sometimes on a level with the surrounding parts, and sometimes 

 depressed, of a firm consistence, and circumscribed. In colour they resemble the 

 grey matter, with numerous vessels distributed through them, and on contact with 

 the atmosphere they assume a rosy hue. 



Microscopically Charcot showed that the apparently definite line of demarcation 

 of a patch was an illusion. He distinguished three concentric zones in which, from 

 the periphery inwards, the changes increased in intensity : — (a) a peripheral zone 

 with thickening of the glia reticulum and increase in size and number of the glia 

 nuclei ; diminution in volume of the myelin sheath ; and unaltered axis cylinders : 



(b) a transition zone in which the glia reticulum is still more hypertrophied and in 

 places replaced by bundles of long and slender fibrils, which are disposed in a 

 direction parallel to the long axis of the nerve fibres ; the nerve tubes are still more 

 atrophied and often represented by the axis cylinders, which may be very enlarged : 



(c) a central zone with the most marked changes. Here all traces of a reticulum 

 have disappeared ; the glia nuclei are shrunken, and may form groups between the 

 closely arranged bundles of fibrils. In the midst of the fibrils persisting axis 

 cylinders are present : these on longitudinal section are thicker than the glia fibrils 

 and never rarefied. This long persistence of the axis cylinders was looked upon as 

 one of the characteristics of disseminated sclerosis, and Charcot ascribed to this 

 fact the absence of secondary degeneration. He so emphasised this finding as to 

 make it a 'differential point in the diagnosis between disseminated sclerosis and 

 disseminated myelitis. 



Charcot further noted alterations in the blood-vessels within the areas. In the 

 peripheral zone even the finest capillaries were prominent, and in the central zone 

 the walls of the vessels were very thickened, and contained numerous nuclei. Fatty 

 granulations were also found in recent areas, not only in the meshes of the recticulum, 

 but also in the walls of the blood-vessel, especially in the transition and peripheral 

 zones. These granulations were thought to be due to the disintegration of the 

 myelin sheath. A peculiar alteration in the nerve cells was described, which was 

 designated " yellow degeneration " ; this was a form of atrophy of the cell, with a 

 disappearance of the cell-processes. 



Charcot related the peculiar intention tremor, so characteristic of disseminated 

 sclerosis, to the absence of the myelin sheath from the long-persisting axis cylinders. 

 The transmission of voluntary impulses would thus still proceed by means of the 

 denuded axis cylinders, but it would be carried on irregularly in a broken or jerky 

 manner, and would thus produce the oscillations which disturb the due execution of 

 voluntary movements. It was thought possible also that the naked axis cylinders 

 might again clothe themselves with myelin, and thus effect a restitutio ad integrum. 



