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respect. The reason why these fibrillæ, and also small nerve-tubes, 
are so distinctly and deeply stained, whilst the sheaths of the larger 
nerve-tubes only get a light reddish staining is, for instance, very 
difficult to explain. Seing, however, that it is only the sheaths of 
the larger nerve-tubes or a layer just inside the sheaths which be- 
comes stained, we may perhaps conclude that this is also the case 
with the smallest nerve-tubes; indeed, we can, to some extent, 
observe it in transverse sections of them, though their contents 
also appear to be somewhat stained. Seeing that it is the case 
with the smallest nerve-tubes from which these fibrillæ issue, and 
which they quite resemble in their staining, it is, in my opinion, 
most probable that they also have an external layer which is the 
essential staining part of them, notwithstanding that the contents are 
also stained. That it is principally the external layers of the fibrillæ 
which are stained, can sometimes be observed, especially in the 
thicker fibrillæ, or in their varicose thickenings. To speak more 
distinctly I will say that I do not think it is the external part of 
the neuroglia-sheaths, but that it is either their internal parts or rather 
a layer inside them which is specially staining in these slender tubes. 
Judging from chromo-silver preparations I think therefore that 
it is probable these fibrillæ are tubes, the smallest of which must 
consequently have an almost infinitesimal diameter. On examination 
of preparations stained with Heidenhains hæmatoxylin method we 
arrive at very similar results; indeed, the tube-structure of these 
slender fibrillæ (which are also partly stained by this method) is 
still more evident. Fig. 65 represents a part of a section through 
such a preparation of the dotted substance (drawn under the cam. 
lue. and very high powers of the microscope). The slender fibrillæ, 
which are deeply stained, are seen longitudinally or transversally trans- 
sected in this very thin section. Transversally transsected they 
appear, partly, as extremely minute meshes, which we have before 
mentioned. Longitudinally transsected they, partly, exhibit very 
distinct longitudinal outlines and a lighter contents. Frequently they 
are, however, so slender, that no such structure can be distinguished, 
neither in transverse sections nor in longitudinal ones. Of the tube- 
structure of these smallest fibrillæ I must, therefore, once more ex- 
pressly say that we do not yet know anything with certainty. 
Another question is, whether are those fibrillæ or tubes only very 
thin primitive tubes which by subdivision etc. have become so thin, 
or are they a special constituent contained in the primitive tubes 
Seeing that they issue from nerve-tubes, I think it is evident that the 
former, or the latter must be the case, tertimn non datum. That they 
