774 DR ALEXANDER BRUCE AND DR JAMES W. DAWSON ON 
is still large, and surface views especially give the impression of its being still central 
or bulging into the lumen. ‘The examination of cross sections gives the true relation of 
the nucleus to the protoplasmic tube (fig. 2). 
A further stage in the evolution of these nucleated tubes, which have resulted 
definitely from the fusion of the fusiform cells, is reached as the contours become 
cylindrical and parallel, and most of the nuclei have taken a peripheral position and 
flattened appearance. The protoplasm still stains homogeneously, but the condensed 
outer border and the sinuously-winding filament become more marked (fig. 3). 
In the loose meshwork there is present only a slight amount of intercellular tissue 
derived from the adventitia of the neighbouring blood-vessels: between the tubes, 
however, distinct glia fibrils, very evident with iron-hematoxylin, run parallel to them. 
Very enlarged glia cells, with thick branching processes, are found in close relation to 
the meshwork. 
Preparations, stained with polychrome methylene-blue, reveal the presence in 
numerous cells of very fine granules, accumulated chiefly at the poles: similar granules 
are found here and there in the protoplasm around the nuclei of the tubes. The 
metachromatic staining of these granules indicates their relation to the granules 
described by Reicu and ALZHEIMER. 
Preparations, stained with iron-hematoxylin-fuchsin, show that these nucleated tubes 
or bands are in various stages of commencing myelination (figs. 14 and 66): some tubes 
show only the pink tinge of the fuchsin (fig. 14q), but all indicate the segmental 
character of the tube in which this differentiation is taking place. The first evidence 
of this is noted in a darkening just within the outer border of the segment (fig. 140); 
this then shows a fine granularity (fig. 14c) and, later, a commencing lattice-work 
appearance (fig. 14d): on cross-section of such tubes, this transition from a homogeneous, 
dark ring or shadow, through the granular stage, to the appearance of dark radial 
peripheral points is also seen, and also the relation of the nucleus to the forming 
myelin (fig. 14/). 
These appearances are undoubtedly those of a commencing myelination of these 
tubes, formed by the alignment and fusion of the fusiform elements. In one strand 
may be recognised tubes which show varying stages in its development (fig. 66). — 
Several writers have pointed out that in its first development in the peripheral nerve 
the myelin is deposited in imbricated, closely applied rings, the spaces between the 
rings representing the future Lantermann incisures. On cross-section such fibres would 
show radial points of myelin at the periphery, and, on longitudinal section, the myelin 
would take the form of a lattice with elongated spaces. 
The appearance of the nucleated tube at this stage, in Van Gieson preparations, is 
not indicative of the structure of a peripheral nerve: the nuclei are much larger and 
more numerous, and the neurilemma sheath is absent. In the stage to be next 
described, where the tubes assume a convoluted disposition, they become more like the 
peripheral nerve fibre in character. 
