756 DR ALEXANDER BRUCE AND DR JAMES W. DAWSON ON 
the outer side, is seen traversing the root at the point of constriction.” Luvi has shown 
that the posterior root fibres lose their neurilemma sheaths and become imbedded in 
neuroglia within the spinal cord in the cervical segments, just as they enter the cord 
in the dorsal segments, but outside the cord in the lumbo-sacral segments. He has 
further shown that the Aufhellungzone or Ablassungzone—the zone which stains 
so palely with the Weigert method—coincides with this transition line, and that here 
the fibres become narrowed to form the so-called “ constriction zone” or ring of Ober- 
steiner. Luvi, Orr and Rows, and others have looked upon this point as the “locus 
minoris resistentiz”’ of the fibre, and have ascribed to it considerable importance in the 
pathogenesis of tabes. 
A similar Ablassungzone has been scarcely recognised for the anterior nerve 
roots, but ORZECHOWSKI in a case of tabes, with the development of numerous pial 
neuromata, found that the abnormal pial fibres were present only in the lumbo-sacral 
seoments and almost exclusively in the neighbourhood of the anterior roots. He noted 
that the position of the Ablassungzone in the anterior roots changed in different 
seoments, even of the lumbar and sacral cord, and that all the abnormal pial fibres 
could be traced to arise from that point of the anterior root fibres peripheral to the 
Ablassungzone, wherever it might be situated. As a rule, it was in the deeper 
layers of the pia or just at the boundary of pia and the glia border layer. 
A very prolonged study of our preparations at all the levels of the cord was carried 
out with the view of tracing, if possible, the point of connection of the fibres, the 
intimate association of which with the anterior roots at once suggested their origin 
from them. | 
In numerous segments in which the secondary fibrosis had not too greatly involved 
the intra-medullary course of the fibres, it was found that the emerging anterior nerves, 
before reaching the pia, show at a definite point of their course a faintly-staining zone — 
(fig. 48). At this point there is a considerable attenuation, possibly even an interrup- 
tion, of the myelin sheath. That this is not due to overdifferentiation is proved by the 
staining of the fine abnormal fibres gathered together in the pia. This transition zone 
differs from that in the posterior roots (fig. 47) in that it is not a constriction zone, for 
the fibres of each group pass parallel through the Ablassungzone before they radiate 
into the root bundle. Further, the point where the myelin sheath becomes attenuated 
is not the same for each group of fibres, so that a line passing through the Ablassung- 
zone of the anterior roots in any one section is a widely-extended and undulating one. 
In the upper cervical segments this Ablassungzone was almost invariably found 
entirely within the glia border layer, or just on its intra-medullary border. In the 
dorsal cord, in those segments sufficiently healthy to allow it to be traced, it was found 
just on the borders of glia border layer and pia. In the lumbo-sacral cord the inereas- 
ing fibrosis in the emerging root zone made it difficult to determine with certainty any — 
regularity in its position. But it could be proved to be an irregular line sometimes 
within and sometimes without the outer border of the glial border layer. 
