THE HISTOLOGY OF DISSEMINATED SCLEROSIS. 685 



the presence of the myelin sheath, there is, as far as we know, no evidence that 

 non-medullated axis cylinders do not transmit impulses as regularly as medullated 

 fibres. Again, fibres lying adjacent to each other in an area do not end necessarily 

 at the same level or in adjacent cells. The leakage, then, if it existed, would 

 take place from the entire circumference, and the result would be not an inco- 

 ordinated act, but a very feeble one, or none at all. Further, the glia meshes in 

 which the naked axis cylinders lie must themselves insulate the fibre. 



The distribution of the areas in all the cases lends support to the view which 

 associates tremor with disturbances of the afferent and efferent extra-pyramidal 

 paths. These, according to Wilson, are respectively the cerebello-rubro-thalamo- 

 cortical path from the nucleus dentatus of the cerebellum, by the superior 

 cerebellar peduncle to the red nucleus of the opposite side, and thence to the 

 inferior and external divisions of the optic thalamus and so to the sensory and 

 motor cortex. The efferent path is the lenticulo-rubro-spinal system, by the ansa 

 lenticularis and sub-thalamic region to the red nucleus, and thence by the rubro- 

 spinal tract of Monakow to the anterior horns of the spinal cord. Lesions of the 

 former path probably remove the inhibitory function of the cortico-petal fibres 

 which pass to the cortical cells, and lesions of the latter remove the normal 

 inhibiting or steadying influence which the corpus striatum exercises on the anterior 

 horn cell. Eeference must again be made to the possibility that in the early 

 stages functional changes may be present, and that the so-called dynamic modi- 

 fication of function may account for many of the early symptoms indicative of 

 defect of cortical control. 



(xiii) Myelin sheath of the nerve fibre. It is held by many writers that the 

 morbid agent has a special affinity for the myelin sheath and for the myelo- 

 axostroma, a constituent element of the axis cylinder, related to the myelin. 

 The question, which is the primary structural element of the nervous tissues 

 attacked by the causal agent, constantly recurs throughout the literature, and 

 from this histological study it will be seen that the change in the myelin sheath 

 must be looked upon as the most constant, the most uniform, and in many cases 

 the primary one. This has all the characters of a primary degeneration in contrast 

 to those of a secondary degeneration, and is due to the destructive or irritant 

 action of the stimulus. The myelin sheath is presumed to have an insulating 

 action : it probably also facilitates the transit of nervous impulses. 



(xiv) Neuroglia. The glia changes set in, as a rule, simultaneously with those 

 in the myelin sheath : the earlier reaction is due to the stimulant action of the 

 morbid agent ; and the later reaction is secondary also to the degenerative processes. 



The glia changes correspond to the age of the process and its intensity : on the 

 one hand glia cell proliferation with the formation of large protoplasmic, potential 



TRANS. EOY. SOC. ED1N., VOL. L, PART HI (NO. 18). 95 



