606 t)R JAMES W. DAWSON ON 



methods have proved that Charcot's conception was justified. Yet this persistence 

 is only a relative one, and in the foregoing study attention has been drawn to the 

 numerous alterations which axis cylinders undergo. The most frequent change is 

 that of a slight homogeneous swelling, and this may be found even in old sclerotic 

 areas, in which, as a rule, the axis cylinder becomes attenuated, and, with diffuse 

 stains, is only with difficulty distinguished from the coarser fibrils. The changes 

 in the axis cylinders are much more easily recognised in longitudinal sections of 

 the nerve fibres. 



In early areas degenerative changes (figs. 425, 426) set in with a moniliform 

 ajjpearance, which may later take the form of spindle-like enlargements of various 

 size, and these may finally lead to disintegration, with the formation of homo- 

 geneous clumps and granules. This qualitative change may affect a large number 

 of the axis cylinders in an affected area, or most of the fibres may show spindle- 

 shaped swellings and only a few go on to the stage of disintegration. It is 

 probable that the fibres which survive the swelling may persist into the stage of 

 sclerosis as homogeneous, condensed elements which, as the sclerosis becomes denser, 

 are compressed into thin, even spiral threads. 



In the stage of abundant fat granule cell formation the swollen axis cylinders 

 become pushed aside between these cells and the proliferated glia elements (figs. 1, 

 2 ; 328, 329), but with specific stains it can be seen that as these cell elements 

 diminish in number and size, the axis cylinders course straight again and are 

 surrounded, almost as by a sheath, with the proliferating, wavy glia fibrils (figs. 3 ; 

 334). At the margin of a demyelinated and even sclerotic tissue, the direct transition 

 of the still remaining axis cylinders into those of the normal tissue can be followed, 

 and if the area be not a very long elongated one, a normal myelinated axis cylinder 

 can be traced, deprived of myelin, right through the sclerosed tissue to its transition 

 into a normal myelinated axis cylinder again. In other cases the transition from 

 normal tissue into sclerotic is marked by a fainter, grey-staining of the axis 

 cylinder, which in the depth of the area becomes a mere shadow (fig. 423), or the 

 transition may be represented by a swelling and tortuosity, which it must be 

 remembered are present to a limited extent in quite normal tissue. If the axis 

 cylinder, too, terminate at the transitional zone, their ends are often swollen and 

 granular. On tranverse section the remains of such degenerated axis cylinders 

 may be recognised as faintly-staining granules — with eosin or picro-fuchsin — or 

 dark-stained, cloudy granular debris — iron and hematoxylin and silver — lying in the 

 meshes of the glia cell protoplasmic processes, and in the walls of the blood-vessels. 



The density of the non-myelinated axis cylinders is rarely the same (fig. 422) 

 as that of the normal fibres, but sometimes they are found of normal calibre and 

 numbers. A striking illustration of this may be seen in figs. 16, 17; 421. In 

 considering the relative proportion of axis cylinders preserved, it must be taken into 

 account that the sclerosed area is relatively smaller than normal, e.g. where the 



