700 DR ALEXANDER BRUCE AND DR JAMES W. DAWSON ON 
fibrillated substance (axis-cylinder). Dogret, AparHy, and Brrue have shown that 
the fibrils within an axis-cylinder can be related not alone to one ganglion cell but to 
several, and also to the peri-cellular network, and that, reciprocally, the network of a 
ganglion cell can be in relation to the fibrils of several axis-cylinders. 
DuRANTE, to whose work we desire to acknowledge our indebtedness, sees in this 
functional grouping of central and peripheral elements an analogy to a gland lobule. 
He proposes the term “neurule” to designate this physiological, polycellular ensemble 
a true primitive nervous lobule. The ganglion cell, charged not to create but to 
receive, perhaps to modify or accumulate, then to expedite the nervous impulse, is 
compared to a gland acinus. The segmental neuroblasts, charged to transmit from 
place to place this impulse to its destination, are compared to the excretory canals. In 
the neurule the elements have a reciprocal dependence in functioning, but may be 
individually independent (e.g. in toxic or infectious conditions). This conception of a 
primitive nervous lobule allows of the nervous system being brought into line with 
other organs and simplifies the understanding of pathological lesions. 
The neurone view teaches that the interannular segment of the peripheral nerve is 
composed of two distinct parts: one, the axis-cylinder, a prolongation of a central cell ; 
the other, the rest of the segment, consisting of myelin sheath, sheath and nucleus of 
Schwann. The cell-chain theory teaches that the interannular segment represents a 
single complete cell element (le newroblaste segmentaire), whose protoplasm has 
elaborated 7 situ the differentiated substances, axis-cylinder and myelin. The axis 
cylinder is regarded no longer as a gigantic cell prolongation of central origin, but 
simply as a bundle of fibrils differentiated in each segmental cell, the myelin also being 
a product of the differentiation of the cell substance. The condensed outer layer of the 
cell substance forms the sheath of Schwann; the original nucleus, pushed to the 
periphery, lies in the thin zone of the remaining undifferentiated protoplasm. In the 
normal functioning nerve tube the differentiated substances preponderate greatly over 
the non-differentiated substance, but the former have, properly speaking, no life of 
their own and disappear in pathological conditions. The non-differentiated substance, 
on the other hand, represents the living element of the cell, and on it devolves the 
role of nutrition, defence, and reproduction ; in pathological conditions it takes up its 
vegetative role, and the cell returns to its embryonic condition. 
The normal histology of the peripheral myelinated nerve fibre, according to this 
view, is the following: In each nerve tube we recognise (1) axis-cylinder, (2) myelin, 
and (3) the sheath of Schwann, a thin membrane limiting the nerve tube on the out- 
side; between it and the myelin lies (4) the nucleus of Schwann in a thin zone of 
undifferentiated protoplasm—normally scarcely visible. The myelin is interrupted at 
regular intervals at the nodes of Ranvier, and the portion of the nerve fibre comprised 
between two constrictions constitutes the interannular segment. Hach segment con- 
tains usually only one nucleus and has the import of a highly differentiated cell. 
The axis-cylinder is formed of two substances, conducting fibrils (the primitive 
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