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centre of many large nerve-tubes. If we now examine similar nerve- 
tubes in transverse and longitudinal sections we will find that, their 
contents consist of a bundle of slender cylindrical primitive tubes, 
quite in the same way as that just mentioned. The only difference is 
that, their central primitive-tubes have a smaller diameter and thicker 
walls, and are more deeply stained than the peripheral ones, it 
seems, indeed, as if they may have been pressed more tightly 
Ptogether and thus been obliged to occupy a smaller space, as they have 
on the other hand got a hrmer consistency, with thicker walls. In 
this axis, and in its neighbourhood, larger dark granules, as mentioned 
above, also occur more frequently than anywhere else, which 
perhaps contributes somewhat to the darker staining. In some nerve- 
tubes this concentration and forming of an axis is so far developed 
that it, in transverse sections (fig. 3), appears as a, by osmic-acid 
and hæmatoxylin, deeply stained spot in the centre of the tube. 
In this spot it is not easy to distinguish any structure or primitive 
tubes, but in extremely thin sections, and by very high powers, it 
is, however possible to see slender tubes with thick, deeply stained, 
walls or membranes in which granules occur. In longitudinal sections 
a longitudinal striation appears as in fig. 4. In one end (fig. 4, a) this 
section has passed through the periphery of the axis and, here, a 
striation is distinctly visible; in the other end (fig. 4, aJ) the section 
has, however, passed more through the centre of the axis and, here, 
the staining is so deep that almost no striation is visible, all the less 
from the section being somewhat thick. 
Usually however this concentration is not so distinctly developed 
as here. Nay, we can indeed find every degree of development, 
from the primary state where no concentration at all can possibly 
be traced to have tåken place, up to an axis as described. 
Fig. 2, t, t\ t^^ thus represent sections of fibres with different degrees 
of concentration, from a very slight one where we can only see 
that the primitive tubes are somewhat deeper stained in this central 
part than in the rest of the tube and in some nervn-tubes even this 
I is not visible (f). 
I It is the nerve-tubes with such an axis that, previous writers 
m have called myeloid fibres ; with what right we will, on a later 
occasion, have an opportunity of examining. 
However we consider this formation of an axis ; in one thing 
we cannot be in doubt, viz., that the whole contents of the 
nerve-tubes, wether they have an axis or not, is of real nervoiis 
nature, because the constructing element in the toliole contents through- 
